Engine Performance
Which of the following is used to prevent EGR operation when the engine Is cold? A. EGR valve position sensor B. EGR vacuum solenoid valve C. EGR vacuum regulator D. Thermal vacuum switch
D. A TVS (Thermal Vacuum Switch) is used to prevent EGR when the engine is cold, If the switch is operating properly, it should not allow vacuum flow until the engine reaches a specific operating temperature.
All of the following are symptoms of insufficient exhaust gas recirculation EXCEPT: A. spark knock B. stalling C. surging at cruise D. increased NOx emissions
B. Stalling is a symptom of too much EGR or EGR at the wrong time.
An electrical circuit is being tested using a DMM (Digital Muitlmeter). When measuring voltage in the circuit, Technician A says that the meter should be connected in parallel. When measuring amperage, Technician B says that the meter should be connected in series. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
A voltmeter is always connected in parallel when making a voltage check of a circuit. An ammeter is connected in series with the circuit, so all the current passing through passes through the ammeter.
A vacuum gauge is connected to the intake manifold engine and the engine is run at 2,000 rpm. During the test, the pointer on the gauge fluctuates rapidly between readings of 10 and 22 inches of vacuum. These test results point to: A. a leaking intake manifold gasket B. worn piston rings C. worn valve guides D. a weak or broken valve spring
D. A leaking intake manifold gasket or worn piston rings would not cause a vacuum gauge needle to fluctuate. Worn valve guides would make the needle fluctuate at idle but the needle would steady when engine speed is increased. A weak or broken valve spring will cause a vacuum gauge to fluctuate or jump from low to high readings.
An alternator output harness (pigtail) needs to be replaced. Tech A says that a pencil soldering iron should be used to ensure a good connection. Tech B says that a butt splice sleeve connector will be sufficient. Who is right? A. Tech A only B. Tech B only C Both A and B D. Neither A or B
D. A pencil iron will not produce sufficient heat to maintain the necessary temperature to melt and flow the solder to properly join the wires. Technician B is incorrect because the sleeves, even when crimped, will develop resistance and cause overheating of the wires, leading to failure at the alternator connection.
A V6 engine with distributor less ignition breaks up on acceleration, but gets smoother when reaching cruise. Tech A says a bad coil pack is the problem. Tech B says the cam sensor must be replaced. Who is right? A. Tech A B. Tech B C. Both D. Neither
A. A cam sensor will have no effect on acceleration. A defective coil pack will break down under the stresses of hard acceleration, and run more smoothly when those stresses are eliminated. However, a roughness in the idle will still be detectable.
Tech A says a high spike line on an oscilloscope indicates disconnected or open plug wire. Tech B says a high spike line indicates a closed gap on a spark plug. Who is right? A. Tech A B. Tech B C. Both D. Neither
A. A higher-by-comparison spike line on an oscilloscope could indicate a disconnected or open spark plug wire. If a spark plug gap were closed, the oscilloscope would indicate a very low spike line.
A vehicle has sluggish performance and high fuel consumption. Testing reveals that the vehicle fails to enter closed loop operation. Tech A says the ECT sensor may be defective. Tech B says the TP sensor may be set incorrectly. Who is right? A. Tech A B. Tech B C. Both D. Neither
A. Although there may be a slight discrepancy in the setting of the TP sensor, it is not relevant to the question. If the coolant temperature sensor tells the PCM/ECM that the engine has not yet warmed up, even though it has, the system will not go into closed loop operation and will run rich.
The engine in a vehicle running at normal operating temperature has a rough idle and black smoke coming from the exhaust. All of the following could be the cause EXCEPT: A. EGR valve stuck closed B. EVAP canister purge solenoid stuck open C. fuel pressure too high D. fuel injector(s) stuck open
A. An EGR valve that is stuck dosed could cause spark knock or other driveability problems, but would not cause rough idle and black smoke. An EVAP canister purge solenoid that was stuck open could be the cause because it would cause the canister to improperly purge at idle. High fuel pressure could be the problem because it would cause more fuel to be injected per injector opening. Fuel injectors that were stuck open would allow fuel flow when they were not energized and could also be the cause of the problem.
The SFT value on a scan tool is shown with a negative number. Which of the following will also be true? A. There Is less oxygen in the exhaust B. The voltage signal from the oxygen sensor decreased. C. The injector pulse width was lengthened. D. The SFT value is greater than 1.
A. An SFT with a negative number means the injector pulse width was shortened, so answer C is wrong. A shortened injector pulse width means that the SFT value was decreased below 1, so answer D is wrong. The SFT will decrease in response to an increased voltage signal from the oxygen sensor, so answer B is wrong. A rich mixture, one with less oxygen, will increase the voltage signal from the oxygen sensor.
A vehicle's tailpipe emissions are being checked with a four-gas exhaust analyzer. The level of CO2 in the exhaust gas is lower than normal and the level of O2 is high. Technician A says that the engine has a lean condition. Tech B says that, if the analyzer had five-gas capabilities, the NOx level would be low. Who is right? A. Tech A only B. Tech B only C Both A and B D. Neither A or B
A. Any deviation, rich or lean, from the optimum air/fuel ratio will cause the C02 level in the exhaust to drop. Higher 02 levels indicate a lean mixture, while lower levels mean a richer mixture. Technician B is wrong because lean air/fuel mixtures can cause high levels of NOx in the exhaust.
Blue smoke is coming from the exhaust pipe of a vehicle. Tech A says that worn piston rings could be the cause. Tech B says that a bad head gasket could be the cause. Who is right? A. Tech A B. Tech B C. Both D. Neither
A. Blue smoke means the engine is burning oil, which could be caused by worn piston rings. Technician B is wrong because a bad head gasket would cause coolant to leak into one or more cylinders, resulting in white exhaust smoke.
An engine with an electronic fuel injection system has high fuel pressure at idle. This could be caused by a: A. low manifold vacuum B. leaking fuel pump check valve C. plugged fuel injection valve D. high manifold vacuum
A. If the manifold vacuum is low, the fuel pressure regulator will restrict the fuel return and increase the fuel pressure.
Tech A says that an incorrect ignition pick-up coil gap can cause a misfire. Tech B says that when testing the pick-up coil with an ohmmeter, the meter should read infinity when the ohmmeter is connected to both pick-up coil leads. Who is right? A. Tech A B. Tech B C. Both D. Neither
A. Pick-up coil gap that is too small or too large may cause engine misfire. Technician B is wrong because the normal resistance reading is 500 to 1500 ohms when an ohmmeter is connecced to the pick-up coil leads. The ohmmeter should read infinity when the ohmmeter leads are connected to ground and either pick-up coil connector lead.
The MIL is illuminated on a late-model vehicle that is brought in for service. A scan tool is connected to the DLC and the DTC PO107 is obtained. Technician A says that this code indicates a failure in the vehicle's powertrain. Technician B says that this code is manufacturer specific. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
A. Technician A is right because the alpha character indicates the area of the vehicle where the failure occurred: B for Body, C for Chassis, P for Powertrain, and U for Network. Technician B is wrong because Manufacturer specific codes have the number 1 as the first digit. DTC P0l07 has a zero as the first digit, so it is a generic code, common to all manufacturers.
All of the following are true of the EVAP canister vent solenoid EXCEPT: A. It is activated by the PCM/ECM to allow the flow of fuel vapor from the EVAP canister to the engine. B. It is activated by the PCM/ECM to block the entrance of outside air into the canister during the EVAP leak test. C. It is used only on vehicles with enhanced EVAP systems. D. It is located in the fresh air supply hose to the canister.
A. The canister purge solenoid, not the vent solenoid, is activated by the PCM to allow the flow of fuel vapor from the EVAP canister to the engine.
Tech A says that valves should be adjusted when the piston is at TDC on the compression stroke and both valves are closed. Tech B says that hydraulic lifters should be adjusted to zero lash. Who is right? A. Tech A B. Tech B C. Both D. Neither
A. To adjust valve lash for one cylinder's cam lobes, rotate the crankshaft so that its piston is at TDC on the compression stroke. This will position the intake and exhaust valve lifters or cam followers on the base circle of their respective cam lobes. With the engine in this position, the valve lash can be adjusted. Technician B is wrong because hydraulic lifcers must be adjusted to position the lifter plunger within the lifter body, therefore the adjuster must be turned further than zero lash.
An alcohol in fuel test is being conducted using a 100mL container. If there is l5mL of water in the container at the end of the test, what is the alcohol content of the fuel? A. 5 percent B. 10 percent C. 15 percent D. 20 percent
A. To test the alcohol content of fuel, fill a lOOmL container to the 9OmL mark with fuel, then fill to the lOOmL mark with water. Close the container and shake vigorously for 10-15 seconds, then allow the contents to settle. Any alcohol that is in the gasoline will be absorbed by the water and settle to the bottom of the container. If there is now l5mL of water in the container, there was 5% alcohol in the fuel.
An engine has a light metallic knocking noise during light engine loads, however, when the cylinder with the noise is disabled during a cylinder balance test, the sound diminishes. Technician A says that the noise is caused by excessive connecting rod bearing clearance. Technician B says that the noise is caused by excessive piston-to-wall clearance. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
A. When you eliminate the ignition or injection co a cylinder with a rod knock, the sound diminishes. Unlike a connecting rod bearing noise, piston slap does not quiet down and may in fact grow louder when you eliminate ignition or fuel injection to that cylinder.
A vehicle with a normally closed canister purge solenoid is not purging the EVAP canister when engine operating conditions for purging are met. When the purge solenoid is removed from the vehicle for testing, it allows vacuum flow when voltage is applied. Technician A says the purge solenoid is defective. Technician B says the purge solenoid power circuit is at fault. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
B. A normally closed purge solenoid should allow vacuum flow when activated by the PCM/ECM, so the purge solenoid is functioning properly. If the purge solenoid is being commanded by the PCM/ECM, then the problem is in the power supply to the purge solenoid.
With the engine off, vacuum is applies to a positive back pressure EGR valve using a hand held vacuum pump. Tech A says that the EGR valve should open. Tech B says that the valve will not open unless a restriction is created in the exhaust and the engine is started. Who is right? A. Tech A B. Tech B C. Both D. Neither
B. A ported or negative back-pressure EGR valve will open when the engine is off and vacuum is applied with a hand operated vacuum pump. A positive backpressure EGR valve needs ex|lausc backpres- sure co open. This can be simulated for testing purposes by placing a restriction in the exhaust pipe, starting the engine and placing the transmission in gear. The engine should stall when the restriction created exhaust back pressure builds up enough to open the EGR valve at idle.
Engine detonation (knock) could be caused by any of the following EXCEPT: A. a lean air/fuel mixture B. retarded ignition timing C. excess carbon in the combustion chambers D. a stuck-closed EGR valve
B. Advanced ignition timing will cause knock, but retarded timing will not.
When troubleshooting a slow drain on the battery, which diagnostic tool should be used? A. ohmmeter B. ammeter C. voltmeter D. test light
B. Always use an ammeter to troubleshoot a slow drain in an automotive electrical circuit.
A sweep test is being made on a TP sensor using the data from a scan tool. Technician A says this is the preferred method for greatest accuracy. Technician B says that a scope will give the best results. Who is right? A. Technician A only B" Technician B only C. Both A and B D. Neither A or B
B. Erratic readings or a momentary infinite reading indicates a defective sensor. Since the processed data of a scan tool can 'skip' several moments during the sweep, allowing dropouts to be 'hidden' during the time between updates of screen data, the voltage test of a TP sensor is best accomplished using a scope, as even the smallest dropouts can be easily seen as the throttle is moved.
A vehicle is towed in with a 'no start' condition. The technician disconnects the coil wire from the distributor cap, connects a suitable spark tester and checks for a good spark while cranking the engine. If there is no spark, all of the following could be the cause EXCEPT: A. a problem in the ignition primary circuit B. a problem in the ignition secondary circuit C. a bad coil D. a bad distributor pick-up coil
B. There would only be a problem in the ignition secondary circuit if there were a good spark. If there is no spark, the problem is in the primary circuit. Since the primary windings of the coil and the distributor pick-up coil are part of the primary circuit, they are possible causes of a no-spark condition.
Tech A says that spark advance on an engine can be tested by listening to the way the engine sounds at higher rpm. Tech B says that spark advance on an engine can be tested with a timing light that incorporates an ignition advance meter. Who is right? A. Tech A B. Tech B C. Both D. Neither
B. To accurately measure spark advance, use a timing light that incorporates an ignition advance meter. The spark advance cannot be determined by listening to the way the engine sounds.
The MAP sensor voltage on a vehicle is measured with the engine running at idle and found to be almost 5 volts. Technician A says that this voltage is too high for idle speed. Technician B says that this voltage will cause the engine to run extremely rich. Who is right? A. Tech A only B. Tech B only C Both A and B D. Neither A or B
C. A high voltage reading at the MAP sensor should indicate atmospheric pressure inside the intake manifold, which should only happen when the engine is off or at WOT (Wide Open Throttle). Since the engine is running, the PCM/ECM will think the engine is at WOT and richen the fuel mixture accordingly.
A vehicle with electronic fuel injection gets poor gas mileage. Engine test show a rich mixture. Tech A says that a bad O2 sensor could be the cause. Tech B says that a bad IAT sensor could be the cause. Who is right? A. Tech A B. Tech B C. Both D. Neither
C. Both the oxygen sensor and the intake air temperature sensor relay signals to the PCM/ECM that directly affects the control of fuel.
A regular customer presents his vehicle for service. He describes symptoms of poor drivability and says that the vehicle has been repaired for the same problem in the past. Which, of the following, should you do first? A. connect the vehicle to an engine analyzer B. check for diagnostic trouble codes C. check the vehicle service history and check for TSBs, service campaigns and recalls D. perform a cylinder balance test
C. Checking the vehicle service history may get you pointed in the right direction before you even raise the hood. What repairs have been performed and what parts were installed? What fixed the car before? If it is a recurring problem, maybe a different course of action is in order. If the vehicle really has failed in the same way, checking TSBs may provide information on updated parts that weren't available previously and may solve the problem now. When checking for service campaigns and recalls, you may find that the problem is a defect that the manufacturer will repair.
TechA says that excessive resistance in the voltage side of the charging circuit can cause a low charging rate. Tech B says that too much resistance in the circuit will cause higher than normal voltage drop. Who is right? A. Tech A B. Tech B C. Both D. Neither
C. Excessive resistance in the voltage and/or ground sides of the charging circuit can cause a low charging rate due to the difference between alternator output and electrical system voltage requirements. The voltage available at any point in the circuit depends on the circuit resistance. The higher the resistance, the more voltage is needed to force current through the circuit. A high voltage reading when performing a voltage drop test is a sign of too much resistance.
All of the following are indications of a charging system that is undercharging EXCEPT: A. slow cranking B. dim headlights C. short light bulb life D. low ammeter indication
C. Overcharging is indicated by short light bulb life and a battery that continually needs water.
Which of the following sensors can be checked by measuring the pulse width of the fuel injector? A. TP (Throttle Positon) sensor B. VSS (Vehicle Speed Sensor) C. MAF (Mass Air Flow) sensor D. CKP (Crankshaft Position) sensor
C. Pulse width is a measurement of how long the fuel injector is open, or how much fuel the fuel injector is delivering. The longer the PCM/ECM grounds the injector, the longer the injector sprays. The longer the injector sprays, the richer the mixture becomes. The Less the injector sprays, the leaner the mixture. Restrict the air intake and look for a change in fuel control. If a change in fuel delivery is noticed, the MAF sensor is most likely working properly.
A vehicle with an AIR system backfires during acceleration. Which of the following should the technician check? A. operation of exhaust manifold check valve(s) B. output pressure of the air pump C. operation of the air bypass valve D. the AIR manifolds for restriction
C. The air bypass valve momentarily exhausts the air pump's output by diverting it to the atmosphere during engine acceleration. During acceleration, the fuel injectors inject more fuel, providing a richer mixture. If oxygen is pumped into the exhaust manifold during this time, a backfire results when the excess hydrocarbons are burned.
A vehicle has been towed in with a no-crank condition. The starter solenoid is being tested using a jumper wire between the battery and the solenoid 'S' terminal. Technician A says that if the engine cranks, the problem is In the starter control circuit. Technician B says that if the solenoid makes a clicking sound, it is operating properly and the starter may be defective. Who Is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
C. The solenoid would be defective in this test if it made no noise and did not click or activate the starter.
Technician A says an oscilloscope can be used to read spark plug firing voltage. Technician B says an oscilloscope can be used to check the ignition coil. Who is right? A. Technician A only B. Technician B only C. Both A and B D, Neither A or B
C. The spark plug firing voltage can be determined as well as the condition of the ignition coil by using an oscilloscope.
While the engine is running, a tech pulls the PCV valve out of the valve opening and places his finger over the valve. No vacuum is felt. Tech A says that the PCV valve could be stuck closed. Tech B says that the hose between the intake manifold and the PCV valve could be plugged. Who is right? A. Tech A B. Tech B C. Both D. Neither
C. The valve should be removed from the hose and shaken. If the valve rattles when shaken, it is not stuck open or dosed. The hose from the intake manifold to the PCV valve is most likely plugged.
A PCM/ECM is being replaced with a rebuiit unit. Technician A says to disconnect the negative battery cable prior to replacement. Technician B says to test the vehicle driver circuits for low resistance. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
C. Use the checklist provided with the rebuilt unit to test the circuits that will connect to drivers in the new PCM/ECM, to be certain that no circuits will draw excessive current.
Blue-gray smoke comes from the tailpipe of a vehicle during deceleration. Tech A says that this is most likely due to bad valve seals. Tech B says that the cause could be clogged oil return passages. Who is right? A. Tech A B. Tech B C. Both D. Neither
C. When a vehicle suffers from worn valve guides and/or bad valve stem seals, you'll see exhaust smoke during deceleration because the high intake vacuum that occurs during deceleration draws the oil through the worn guides or seals. However, before you blame either the valve guides or the valve seals, verify that all of the oil return holes are clean. If oil cannot drain freely back into the crankcase, it can accumulate in the head and be drawn by vacuum ihto the combustion chamber, causing exhaust smoke.
When manifold vacuum is checked on a vehicle brought in for service it is found to be low but steady. Technician A says that an air/fuel mixture that is too rich can cause this condifion. Technician B says that an air/fuel mixture that is too lean can be the cause. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
C. When the idle vacuum is low but steady, suspect an air/fuel mixture that is too lean or too rich. Air leaks or vacuum leaks can cause a lean condition and are common causes of rough idle, hesitation, stalling and hard starting. If the mixture is artificially enriched by injecting propane into the induction system, an engine running lean should speed up and the vacuum reading should rise. If the air/fuel mixture is too rich, the engine will slow down and the vacuum reading will drop. If the engine Is running lean and you suspect a vacuum leak as the cause, try using a propane kit with a length of hose attached to find the leak. Pass the hose end around the suspected areas and listen for a change in idle.
A vehicle's exhaust system is being tested for a restriction, using a vacuum gauge connected to the intake manifold. All of the following are indications of a restricted exhaust EXCEPT: A. When the engine is gradually accelerated to 2000 RPM, the vacuum reading slowly drops to zero and slowly returns to normal. B. When the throttle is closed, the vacuum does not increase. C. When the thrott!e is closed, the vacuum momentarily increases and then resumes the normal reading. D. When the engine is accelerated to 2500 RPM, the vacuum reading drops 3 in. Hg below the original reading after a few minutes.
C. When the throttle is closed on a properly operating vehicle with a good exhaust system, the vacuum should momentarily increase and then resume the normal reading. All of the other answers describe indications of a restricted exhaust system.
All of the following can cause air flow problems through a radiator core EXCEPT: A. broken shroud B. debris buildup C. bent fins D. excessive mineral deposits
D. Excessive mineral deposits can restrict coolant flow through the radiator, but would have no effect on air flow. A broken fan shroud would cause less than optimal air flow through the radiator core. Debris and bent fins would block air flow through the core.
When testing computer-controlled systems, a DMM (Digital Multimeter) should be used with an input impedance of at least: A. 10k ohms B. 100k ohms C. 1 megohm D. 10 megohms
D. For maximum protection to the computer-controlled system or any electronic circuit, it is best to use ac least a 10-megohm impedance DMM.
Hall effect sensors normally produce a: A. sine waveform B. triangle waveform C. sawtooth waveform D. square waveform
D. Hall effect sensors produce a square wave pattern. Sine waveforms are produced by two-wire, reluctor (permanent magnet) sensors.
All of the following are true statements regarding intermittent faults EXCEPT: A. An intermittent problem is a malfunction that occurred in the past, but is not present at the time of the self-test. B. You may have to try to recreate conditions described by the driver to get an intermittent code to reset. C. intermittent problems are often caused by damaged wiring and connectors, so tapping and wiggling wiring harnesses and connectors can sometimes get problems to reoccur and reset codes. D. Intermittent faults should be serviced before hard faults.
D. Hard faults should be serviced before intermittent faults.
Which of the following would cause a spark miss? A. high engine temperature B. low fuel pressure C. dirty throttle body and IAC D. distributor cap carbon track
D. If the power if diverted to ground before reaching the spark plug, a spark miss will result.
The EVAP system is designed to: A. keep fuel vapors from escaping the fuel tank B. capture fuel vapors and route them to the catalytic converter, where they are burned C. purge fuel vapors from the charcoal canister to atmosphere D. capture fuel vapors and route them to the engine where they become part of the air/fuel mixture and are burned during combustion
D. The purpose of the evaporative emissions control system (EVAP) is to prevent HC emissions from escaping the fuel system to atmosphere. Prior to the introduction of EVAP systems, fuel vaporized and was emitted to the atmosphere from vented gas caps and carburetor float bowls, polluting the environment. The EVAP system is designed to capture these vapors and route them to the engine where they become part of the air/fuel mixture and are burned during combustion.
Technician A says that a secondary air injection system forces air into the intake ports. Technician B says that the secondary air injection system reduces spark knock. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
D. The secondary air injection system injects air into the exhaust system. Since the secondary air injection system is used after the combustion event, it cannot reduce spark knock.
A technician Is testing the ignition on a vehicle with a 'no start' condition. He connects a test light between the negative side of the coil and ground and has an assistant crank the engine. A test light that flutters on and off indicates all of the following EXCEPT: A. The pickup coil signal is OK. B. The ignition module is OK. C. The module is triggering the ignition coil to fire. D. The coil is OK.
D. The test light fluttering on and off means that tile coil is being triggered to fire, it is not a test of the coil itself.
Which of the following diagnostic methods can be used to determine which cylinder is leaking combustion chamber gas into the cooling system? A. observing the radiator coolant for bubbles while the engine is running B. placing a vial of a chemical that is sensitive to combustion gases over the radiator filler neck while the engine is running C. holding an exhaust analyzer probe over the radiator filler neck while checking for a reading on the exhaust analyzer D. observing the radiator coolant for bubbles while performing a cylinder leakage test
D. While each of these methods can be used to determine whether there is a combustion chamber leak into the cooling system, only a cylinder leakage test will identify which cylinder is leaking.
A technician suspects that a faulty CMP (Camshaft Position) sensor is the cause of a driveability complaint. In order to test the sensor, he must first know what type it is. Since the sensor is equipped with a 3-wire connector, the sensor: A. is a Hall effect type B. is a magnetic reluctance type C. creates a voltage D. is a permanent magnet generator
A. Hall Effect switches are equipped with a 3-wire connector. Magnetic reluctance types are equipped with a 2-wire connector. They create a voltage and are also known as PM (Permanent Magnet) generators.
After the compression readings shown above were taken, a wet compression test was made. The second set of readings was almost the same as the first. Tech A says that a burned valve could cause these readings. Tech B says that a worn piston ring could cause these readings. Who is right? A. Tech A B. Tech B C. Both D. Neither
A. If a piston ring is leaking, usually a wet compression test will indicate some compression. If a valve is burned, a wet compression test will make no difference and indicate the same compression readings.
While testing a starting circuit on a V8 engine, the tech finds that the engine cranks slowly, the starter current draw is 90 amps, and the battery voltage while cranking is 11 volts. What should the tech do next? A. Check the voltage drop of the starter motor circuit. B. Test the battery capacity. C. Replace the starter motor, as a short is indicated. D. Determine the condition of the engine.
A. If an engine cranks slowly and the starter current draw is 90 amps and the voltage is 11 volts, the technician should next check the voltage drop of the starter motor circuit.
With DMM connected, the O2 sensor reads above 550 millivolts constantly, Tech A says that the fuel mixture is probably too rich. Tech B says the fuel mixtures may be too lean or there may be an exhaust leak near the sensor. Who is right? A. Tech A B. Tech B C. Both D. Neither
A. The computer reacts to the oxygen sensor signal by adjusting the fuel metering at the injectors. Too high a voltage indicates a rich mixture.
An oxygen sensor voltage is being monitored on a scope type analyzer. A pattern is observed to change topped 'hills'. Tech A says that this normal, closed loop operation. Tech B says that this indicates intermittent operation, and the sensor needs replacement. Who is right? A. Tech A B. Tech B C. Both D. Neither
A. The distinctive pattern described is a normal closed loop, adaptive fuel management pattern. A defective pattern would be a steady high or low voltage when conditions do not dictate that reaction.
A vehicle can be started with great difficulty, but lacks power, and will not idle. Tech A says that there could be a hole or tear in the duct between the mass air flow sensor and the throttle body. Tech B says that a restricted fuel filter is the problem. Who is right? A. Tech A B. Tech B C. Both D. Neither
A. The fuel filter may be in need of service, but it is not the cause of the problem. Unmetered air entering the engine means that there is more air than the amount for which the engine is delivering fuel. A careful examination of the duct between the air flow sensor and the throttle body should reveal where the unmetered air is entering.
There are two types of MAP sensors: the analog signal type, which is tested with a voltmeter, and the frequency signal type, which is tested with a Hertz meter or digital tachometer. To determine which type the technician has, he performs a reference voltage and signal voltage check. The signal voltage doesn't change from 2.5 volts. It is most likely: A. a frequency type B. an analog type C. could be either type D. none of the above
A. The sensor measures pulses received per second (Hz) and converts them to revolutions per minute. A constant signal voltage is necessary.
Two technicians are inspecting an exhaust system. When he taps on the muffler with a mallet, Techician A hears noise coming from inside the muffler and says that it is most likely rotting out from the inside. Technician B says that he hears noise coming from inside the catalytic converter when he taps on it with a mallet and says that the converter is rotting out from the inside. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
A. When inspecting an exhaust system, tap on the muffler with a mallet and listen for the sound of loose rust particles. Mufflers usually rot out from the inside, so even if the outside of the muffler appears OK, it still may be ready for replacement. Technician B is incorrect because if a rattling sound is heard coming from a catalytic converter when it is struck with a mallet, it means that the ceramic substrate has come loose and is disintegrating.
All of the following are true statements regarding fuel pressure regulators EXCEPT: A. With the vacuum line connected to the fuel pressure regulator, fuel pressure should be higher than with the line disconnected. B. Most fuel pressure regulators are not adjustable. C. Most fuel pressure regulators are connected to manifold vacuum and vary the fuel pressure according to engine load. D. Some regulators can suffer from a ruptured diaphragm, allowing fuel to be sucked into the intake manifold through the vacuum line, which operates the regulator, causing a rich running condition.
A. With the vacuum line connected to the fuel pressure regulator, fuel pressure should be lower than with the line disconnected.
When testing a catalytic converter with an exhaust pyrometer, the difference between the surface temperatures of the converter inlet and outlet should be ________ with the engine at normal operating temperature. A. 50ºF (10ºC) B. 100ºF (38ºC) C. 150ºF (66ºC) D. 200ºF (93ºC)
B. A simple test for whether a catalytic converter is functioning properly is by measuring the inlet and outlet temperatures. With the engine at normal operating temperature, check the temperature of the exhaust inlet and outlet surface before and after the converter using a temperature probe and a DMM or an exhaust pyrometer. The exhaust surface temperature should be at least 100 degrees F (38~C) hotter than the intake surface temperature. If not, the converter is probably not operating at peak efficiency.
A technician wants to quickly compare the secondary ignition patterns of each cylinder of a V8 engine. Which of the following scope patterns should he use? A. primary superimposed B. secondary superimposed C. parade O. raster
B. Answer A is wrong because the technician wants to see the secondary ignition pattern. The secondary superimposed pattern places all patterns on top of one another to check for uniformity Any pattern that does not align with the others can indicate a problem with chat cylinder. Once a problem cylinder has been identified, the other patterns can then be used to determine which component is causlng the problem.
A poor running vehicle has low fuel volume. Tech A tests the electrical connector at the tank, and finding system voltage available, says the vehicle needs a new pump. Tech B says high circuit resistance may prevent the pump from operating properly. Who is right? A. Tech A B. Tech B C. Both D. Neither
B. Before the energy reaches the fuel pump, it must pass through the pump harness, pass-through connector, and the pump wiring. A high resistance in any of these places can keep the pump from rumling properly. When testing for available pump voltage, remember that there is virtually no load placed on the pump circuit by a multimeter. A test light can load the circuit in place of the pump to determine if there is a resistance, which will cause a significant drop in the voltage available to the pump. A typical resistance in this instance could be relay contacts, which are burned or have insufficient pressure.
A vehicle with electronic ignition hesitates and stumble during acceleration. The problem goes away when the vacuum advance hose is disconnected and plugged. Tech A says that a stuck vacuum advance mechanism could be the cause. Tech B says that an intermittent open in the pickup coil leads could be the cause. Who is right? A. Tech A B. Tech B C. Both D. Neither
B. If a vacuum advance mechanism were stuck, the problem would not change if the vacuum hose is connected or disconnected. When the vacuum changes to the vacuum advance mechanism and the distributor plate moves, this may move the wires to the pick-up causing a short or open which would cause the pick-up signal to be lost momentarily.
Two technicians are discussing alcohol in fuel. Technician A says that if any alcohol is mixed with gasoline it will cause driveability problems. Technician B says that excessive amounts of alcohol in fuel can degrade the fuel system. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
B. If an excessive amount of alcohol is mixed with gasoline in vehicles not designed for it, it can degrade rubber fuel system components, clog the fuel filter and cause a lean air/fuel mixture. Technician A is wrong because gasoline mixed with up to 10% alcohol (ethanol) Is used in many parts of the U.S. The small percentage of alcohol is generally used to increase the octane rating and decrease carbon monoxide emissions.
The initial timing and spark advance are being checked on an older vehicle with distributor ignition. Tech A says that the engine must be accelerated when checking how much the timing is being advanced by the distributor vacuum advance unit. Tech B says that the vacuum line to the vacuum advance should be disconnected and plugged before checking the ignition timing. Who is right? A. Tech A B. Tech B C. Both D. Neither
B. Initial timing can be adjusted on these systems after the vacuum hose is disconnected from the advance unit and plugged. Technician A is wrong because the engine must be accelerated only to check mechanical advance. The vacuum advance unit can be checked using a timing light and a vacuum pump. Check the timing advance while applying vacuum to the advance unit with the pump.
When an EGR valve diaphragm is raised with the engine idling, there is no effect on idle speed. Technician A says that the EGR valve is bad and should be replaced. Technician B says that the EGR passages are clogged with carbon. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
B. Manually raising the EGR diaphragm when the engine is idling should allow exhaust gas into the intake air stream, which should stall an engine at idle. Since this had no effect on the idle speed, we know that there is no exhaust gas flow, so replacing the EGR valve would have no effect. Technician B is correct because the lack of exhaust gas flow is most likely caused by carbon buildup in the EGR passages.
A customer brings his car in because the MIL is on. However, when the vehicle is started in the service bay, the light is off. Technician A says this is because the OTC that turned on the light is no longer in the PCM/ECM's memory. Technician B says this is because the monitor responsible for the OTC has run three times in a row without seeing the same failure. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
B. Technician A is wrong because the DTC will remain the PCM/ECM~s memory until a specific number of warmup cycles have been completed.
A voltage generating Vehicle Speed Sensor (VSS) is being tested. Technioian A says that the transmission shaft should be rotated and the DC voltage out-put checked. Technician B says that the sensor resistance should be checked. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
B. Technician B is correct because the amount of resistance in a VSS can be checked with an ohmmeter. Technician A is incorrect because when VSS voltage is checked, the meter should be on the AC setting. The VSS is a permanent magnet generator that produces an AC signal. When checked with a lab scope, this signal will appear as a sine wave pattern.
A vehicle is towed in for ago start condition. Spark tests good, and an examination of the throttle body shows fuel pouring from the TBI injector when the engine is cranked. Tech A says the fuel injector is stuck open. Tech B says the PCM driver for the injector is shorted out. Who is right? A. Tech A B. Tech B C. Both D. Neither
B. The injector would pour fuel even when the cranking had stopped, until the pressure ran out, if the injector was stuck open. In this case, the injector only pours fuel when it is powered up, indicating a shorted driver in the PCM. You can disconnect the injector to double check this, proving that the injector will hold back fuel pressure.
A vehicle running at normal operating temperature is idling at too high an idle speed. When checking the IAC (idle Air Control) valve pintie counts with a scan tool, the reading is zero. Technician A says that the IAC valve is defective. Technician B says that there is a vacuum leak at the intake manifold. Who Is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
B. Zero counts corresponds to a closed IAC valve passage, which the PCM/ECM would signal to try to close off the air flow, so Technician A is wrong. Since the IAC valve is closed, the high idle speed is most likely caused by air entering from another location, such as a vacuum leak.
Technician A says that a 'pending' code is recorded if monitor results indicate a failure after one drive cycle. Technician B says pending codes should be checked to verify a repair. Who is right? A. Technician A only B. Technican B only C. Both A and B D. Neither A or B
C. A 'trip' is a completed drive cycle. Although some monitors will set a DTC and turn on the MIL if a fault is found after one trip, for most DTCs the PCM/ECM must see the same fault occur during two trips. After the first trip, the fault is recorded as 'pending'. Once the PCM/ECM sees the same fault the next time the monitor runs, the PCM will turn on the MIL. If the same fault is not seen during the next monitor, the pending code will be cleared. Once repairs are completed, operate the vehicle in a manner necessary to satisfy the drive cycle requirements for the monitor that set the DTC. Recheck the monitor status and check for pending codes to see if the fault returned.
Two techs are listening to a tapping noise coming from the top end of a V8 engine. Tech A says the noise could be a valve needing adjustment. Tech B says the noise could be an exhaust leak. Who is right? A. Tech A B. Tech B C. Both D. Neither
C. A tapping noise that does not dissipate after the engine warms up could be caused by worn valvetrain components or excessive valvetrain clearance. A similar type noise can sometimes be caused by an exhaust leak at the exhaust manifold/cylinder head juncture.
Tech A says that evidence of cylinder wear can be found using a cylinder leakage tester. Tech B says that a blown head gasket can be found using a cylinder leakage tester. Who is right? A. Tech A B. Tech B C. Both D. Neither
C. Air blowing into the crankcase during a cylinder leakage test indicates a piston, rings and/or cylinder that are worn. When performing a cylinder leakage test, air that causes bubbles in the radiator coolant indicates a cracked head, cracked block, and/or a blown head gasket.
An IAT sensor is being tested. Tech A says that the resistance should be checked on the NTC (Negative Temperature Coefficient) sensor. Tech B says that the voltage drop across the sensor should be checked on this type of sensor. Who is right? A. Tech A B. Tech B C. Both D. Neither
C. Resistance varies inversely with temperature on an NTC sensor. The sensor's function is usually checked by measuring the resistance between the sensor terminals. Most manufacturers publish resistance/temperature tables, but in general the resistance should be approximately 3000 ohms at room temperature (70'F, or 21'C). Start the engine, and as it warms up check that the values change smoothly, or heat the sensor using a hair dryer to see if the values change smoothly. If the resistance value doesn't change, the sensor is probably defective. The sensor can also be checked by measuring voltage drop. More voltage is dropped across the sensor when it is cold, and less when hot. The PCM/ECM, by monitoring the voltage change, adjusts the amount of fuel injection according to the air temperature. With the sensor installed, back-probe the sensor terminals with a voltmeter connected across the sensor terminals. Compare the voltage readings at various temperatures with the mamlfacturer's voltage/temperature table. The voltage drop can also be seen using a scan tool.
A vehicle with multlport fuel injection has a stalling problem. When the throttle body is inspected if is found to be contaminated with sludge buildup. Technician A says that this could be caused by worn rings. Technician B says that this could be caused by a clogged or restricted PCV system. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
C. The PCM/ECM bases idle speed calculatlons on a set amount of air that bypasses the throttle plates. If this air flow is reduced by accumulated sludge deposits, these calculations will be incorrect and may result in stalling. Worn rings can cause excessive blowby into the crankcase. Excessive blowby can be more than the PCV system can handle, so instead of going into the intake manifold, these gases force their way through the fresh air intake and into the air cleaner. Oil deposits that are part of the crankcase gases can then accumulate on the throttle body when these gases mix with the air entering the engine, eventually causing the sludge buildup. A dogged or restricted PCV valve can cause the same results.
Under which of the following conditions is exhaust gas recirculation required? A. cold engine at part throttle B. warm engine at idle C. warm engine at part throttle D. warm engine at wide open throttle
C. When the engine is warm and above idle speed, EGR is required to prevent spark knock and reduce NOx emissions. Until the engine is warm, there is no need for exhaust gas recirculation because combustion is still sufficiently cool. Even when the engine is warm, there is no need for exhaust gas recirculation at idle because combustion pressures are relatively low and NOx is not formed, and exhaust gas recirculation would stall the engine because of too much dilution. At WOT, the need for power outweighs the need to control NOx emissions, and since WOT needs richer, and therefore slightly cooler mixtures, NOx formation is minimal anyway.
A quick way to determine if valve timing has jumped is to: A. look at the timing mark alignment on the cam and crank sprockets B. check timing chain or belt slack C. check valve movement with the piston at TDC on the exhaust stroke D. check valve movement with the engine at TDC on the compression stroke
C. With the piston ac TDC on the exhaust stroke, both valves should be open slightly because of valve overlap. The exhaust valve should close a few degrees after TDC and the intake valve should open a few degrees before. If the valves do not operate this way with the crankshaft at this position, the valve timing is incorrect. Answer A is wrong because, while this way will achieve a determination, it will most likely take longer to disassemble the front of the engine. Answer B is wrong because looseness in the belt or chain can indicate a strong possibility that the valve timing has jumped, but is not confirmation of the condition.
All of the following are statements describing normal mechanical fan clutch operation EXCEPT: A. A fan clutch has viscous drag regardless of temperature. B. A fan clutch varies fan speed according to engine temperature. C. A fan clutch stops the fan from spinning within two seconds after turning off a hot engine. D. A fan clutch varies fan speed according to engine speed.
D. A properly operating fan clutch will change the speed of the fan according to engine temperature. When the engine is cold, the fan clutch does not turn the fan very fast, even when engine speed is increased. As the engine warms up, the fan clutch increases the speed of the fan. If the fan speed varies only according to engine speed, regardless of temperature, tllen the fan clutch is probably seized and should be replaced.
The wiring diagram symbol shown above is for a: A. resistor B. variable resistor C. transistor D. thermistor
D. A thermistor Is a type of variable resistor that changes resistance according to the change in temperature.
A vehicle gets poor fuel mileage and has poor heater performance. Which of the following could be the cause? A. a bad ECT sensor B. a defective fan clutch C. a clogged cooling system D. a stuck open thermostat
D. A thermostat that is stuck open will not allow the engine to come to the correct operating temperature. Heater performance will be poor because the engine coolant will not be hot enough. The ECT will report the lower temperature to the PCM, which will make the air/fuel mixture richer, causing poor fuel economy.
A turbocharged vehicle performs poorly and lacks power. All of the following could be the cause EXCEPT: A. restricted intake duct B. a waste gate that is stuck open C. failed turbocharger shaft bearings D. a waste gate that is stuck closed
D. A wastegate that is stuck closed would cause overboost. A restricted intake duct, a stuck open wastegace, or failed shaft bearings, which would cause the rotating assembly to bind or drag, would all reduce boost pressure and vehicle performance.
A vehicle is towed in the with a 'cranks but won't start' condition. A 'noid' light test finds no injector pulses, and Tech A says the vehicle need a computer. Tech B finds no spark and says the the vehicle needs an ignition module. Who is right? A. Tech A B. Tech B C. Both D. Neither
D. Although the vehicle may need one of these items before being returned to service, both technicians are jumping to conclusions. A defective crank sensor can cause both of these symptoms, and that is far more likely than either of the other possibilities. The correct action is to test until the defective component is located.
All of the fqllowing are indications of a catalytic converter problem EXCEPT: A. The converter shell appears bluish. B. The converter makes a rattling noise when struck with a mallet. C. There is little difference between the inlet and outlet temperatures. O. The catalyst monitor signal is stable.
D. If the signal from the catalyst monitor fluctuates high and low like the signal from the primary oxygen sensor, it means that the converter is not functioning properly. All of the other answers are indicators of catalytic converter problems. If the converter shell appears bluish, it means chat the converter has overheated. If the converter rattles inside when struck with a mallet, it means that the ceramic substrate has come loose and is disintegrating. The exhaust surface temperature should be hotter than the intake surface temperature. If not, the converter is probably not operating at peak efficiency.
All of the following can interrupt an OBD II PCM/ECM reprogramming procedure EXCEPT: A. getting an automatic virus protection update B. opening a door on the vehicle C. carrying the vehicle's key fob in your pocket D. turning on the ignition key
D. Interrupting a PCM/ECM reprogramming procedure can cause the process to fail and possibly min the PCM/ECM. Getting an automatic update for virus protection software on the PC could interrupt the process, as could opening a door on the vehicle and turning on the interior lights. Many vehicles have security systems that automatically activate when you walk a certain distance from the vehicle. The proximity device is usually incorporated in the keyfob, so carrying it in your pocket could activate the security system and interrupt the reprogramming process. Turning on the ignition key would not interrupt reprogramming and is usually required at some point.
When retrieving stored codes from a computerized engine control system, a hard fault is found regarding a fuel injector circuit. Technician A says that fuel pressure and volume tests should be performed. Technician B says that the injectors should be replaced on that circuit. Who is right? A. Technician A only B. Technician B only C. Both A and B D. Neither A or B
D. Technician A is wrong because a problem with fuel pressure and volume would not set a fuel injector circuit code. Technician B is wrong because the code indicated a malfunction in the fuel injector circuit, and replacing the injectors would be jumping to the conclusion that the injectors are bad. The circuit should be tested in the order specified by the manufacturer's diagnostic procedures before any components are replaced.
All of the following could cause a vehicle with enhanced EVAP to fall the PCM/ECMs large leak test EXCEPT: A. loose fuel cap B. cracked vapor Iine C. stuck open canister vent solenoid D. open canister purge valve
D. The PCM/ECM opens the canister purge valve to cause a vacuum in the EVAP system. All of the other answers are leaks that would prevent a vacuum from being created.
