L1 Practice Exam (Fuel and Air Induction Systems Diagnosis)

81. Technician A says that excessive back pressure caused by a partially clogged exhaust system could cause the plastic connectors on the position sensor to melt. Technician B says to always check for a restricted exhaust whenever replacing a failed EGR valve position sensor. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-Both A and B c. Both technicians are right. Technician A is right because excessive back pressure caused by a partially clogged exhaust system would cause the plastic sensors to melt. Technician B is right because you always check for a restricted exhaust whenever replacing a failed EGR valve sensor.

59. Two technicians are discussing electronic throttle control on the Composite Vehicle Type 4. Technician A says if one APP (accelerator pedal position) sensor or one (TP) throttle position sensor fails, the engine control module will turn on the malfunction indicator lamp and limit the throttle opening to 35%. Technician B says if two or more of the APP and TP sensors fail, the spring-loaded throttle plate will close and the engine will shut down. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-A only a - Tech A is right because if one APP sensor or one TP sensor fails, the ECM will turn on the MIL and limit the throttle opening to 35% (see page 10 of the Composite Vehicle Type 4). Tech B is wrong because when two or more of the APP and TP sensors fail, the spring-loaded throttle plate will close to 15% throttle opening, which is called the LIMP-IN mode, and not completely close the throttle (see page 10 of the Composite Vehicle Type 4).

75. A vehicle comes in the shop with MIL (malfunction indicator lamp) on with DTC P0010 (Camshaft Position Actuator Circuit Bank 1) showing the above data stream. Technician A says the loss of one CMP (camshaft position) sensor could be the cause. Technician B says the TP (Throttle Position) and APP (accelerator pedal position) sensors are frozen. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-A only a - Tech A is right because page 12 of the composite vehicle type 4 states that the loss of one CMP sensor signal results in the MIL on with a DTC stored and the valve timing held at full retard, which the data stream shows. Tech B is wrong because both the TP and APP sensor data shows normal operation.

72. The engine idle is rough and unstable with the following scan tool data on the composite vehicle. Technician A says a partially stuck open EGR valve could be the cause. Technician B says a defective EVAP purge valve could be the cause. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-A only a - Tech A is right because the EGR valve position sensor shows a 75% opening according to the scan data stream (see page 13 of the composite vehicle type 4) and the MAP (Manifold Absolute Pressure) sensor is showing higher than normal pressure in the intake manifold (see page 15). Tech B is wrong because the EVAP Canister Purge Solenoid shows 0% opening and therefore is not open (see page 19 of the composite vehicle type 4).

74. The composite vehicle type 4 stalls occasionally with the above recorded scan data. Technician A says that the EGR (exhaust gas recirculation) valve is sticking. Technician B says that the EVAP (Evaporator Emission) canister purge valve is stuck open. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-A only a - Tech A is right because the scan data shows the EGR (exhaust gas recirculation) valve at a 25% position when it should be closed at idle as indicated by the other data (see page 4 of the composite vehicle type 4). Tech B is wrong because the data stream shows 0% movement of the EVAP canister purge valve (see page 19 of the composite vehicle type 4).

63. Two technicians are explaining emission diagnosis of the fuel system. Technician A says an ignition misfire will increase CO and HC emissions and set a DTC (Diagnostic Trouble Code). Technician B says a misfire caused by a lean condition will increase HC and CO emissions without a DTC being set. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-A only a - Technician A is right because all misfires set a Specific DTC and will increase HC and CO. Technician B is wrong because a lean misfire also sets a DTC and will not increase HC and CO.

78. The HO2S (heated oxygen sensor) on bank 1 is being tested on a fuel-injected 4-cylinder engine. The reading is relatively steady ranging from 0.388 to 0.460 volts. Adding propane increases the voltage to 0.787 volts and creating a vacuum leak lowers the voltage to 0.302 volts. Technician A says the oxygen sensor may be defective. Technician B says there could be a crack in the exhaust manifold allowing outside air to enter the exhaust system upstream from the HO2S oxygen sensor. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-A only a - Technician A is right because if the reading changes from 0.388 to 0.460 volts when adding propane to 0.787 volts, the oxygen sensor is driving lean to rich and creating a vacuum leak lowering the voltage to 0.302 volts, the ECM is driving rich to lean and so the oxygen sensor is working. Technician B is wrong because air entering the HO2S sensor downstream from this sensor would not affect its signals to the PCM (Powertrain Control Module). The HO2S ½ is mounted in the exhaust pipe after the catalytic converter (downstream) and its signal is used to monitor the operation of the other 2 oxygen sensors.

79. Technician A says a crushed PCV hose affects idle on some engines and also can cause an oil leak. Technician B says when checking crankcase pressure at 2500 RPM, the PCV system should show a slight pressure in the crankcase at idle. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-A only a - Technician A is right because on many engines the PCV provides a portion of the idle air and if it is restricted it creates positive crankcase pressure which will push the engine oil out of the engine. Tech B is wrong because the PCV system should create a slight vacuum in the crankcase at 2500 RPM.

67. An engine has a low power complaint with a whistling sound and an exhaust system restriction is suspected. A vacuum gauge is connected to the intake manifold. Technician A says when the engine is kept at a constant speed the manifold vacuum on the gauge will drop gradually if there is a restriction. Technician B says to measure manifold vacuum at a low idle (500 to 1000 RPM). Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-A only a - Technician A is right because vacuum checks here are used for exhaust back pressure. If the exhaust system is restricted, pressure increases in exhaust. This pressure is called back pressure. Manifold vacuum will drop gradually if the engine is kept at a constant speed and the exhaust is restricted. The reason vacuum will drop is that all exhaust leaving the engine at a higher engine speed cannot get through a restriction. Technician B is wrong because you measure manifold vacuum at a high idle (2000 to 2500 RPM).

70. Technician A says a cracked exhaust manifold can affect oxygen sensor operation. Technician B says a clogged air filter element will not affect emissions. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-A only a - Technician A is right because a cracked exhaust manifold allows more oxygen into the exhaust stream, which affects oxygen sensor voltage. Technician B is wrong because a clogged air filter raises Hydrocarbons (HC) and also affects O2 (Oxygen) and CO (Carbon Monoxide) levels.

86. Two technicians are explaining OBD (On-board diagnostics) systems level I and II. Technician A says OBD II systems require misfire detection and a flashing MIL (malfunction indicator lamp) if it affects the catalytic converter. Technician B says OBD I was capable of detecting oxides of Nitrogen (NOX). Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-A only a - Technician A is right because misfires directly affect exhaust emissions and the Clean Air Act requires specific emission levels. OBD II is designed to detect component degradation or faulty emission-related system that prevents compliance with federal emission standards. Regulations for OBD-II vehicles requires a computer to test for exhaust emissions within 1.5 times FTP limits and Flash the MIL if engine misfire could damage catalytic converter. Technician B is wrong because neither OBD I or II is capable of detecting oxides of Nitrogen or NOx. Only DTC (diagnostic trouble codes) for devices that affect NOx output are used for detection.

71. A customer complains of poor fuel economy with the above scan tool data on the composite vehicle. Technician A says the EGR valve may be stuck open. Technician B says the canister purge diaphragm may have a leak. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-B only b - Tech B is right because the data indicates EVAP Canister Purge Solenoid at 100% and the vent solenoid ON. The MAP sensor indicates high pressure in the intake and MAF is showing 110 gm/sec and 4 volts. Tech A is wrong because a stuck open EGR would not cause poor fuel economy and is supposed to be almost fully open at 2500 RPM.

61. Two technicians are discussing open loop on the composite vehicle. Technician A says the composite vehicle goes into fuel cut-off mode above 4,000 RPM (revolutions per minute). Technician B says that, in open loop, the injector pulse width is calculated using the engine temperature and the MAF (Mass Air Flow) sensor. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-B only b - Tech B is right because, in open loop, the AFRS (Air/Fuel Ratio Sensors) are not used for injector calculations until two conditions are met: throttle position of less than 80% and ten seconds since startup and the 2 AFRS sensors are sending varying voltage signals to the engine control module. During that period, injection pulse width is calculated by engine temperature MAF sensors. Tech A is wrong because, on page 8, the RPM is stated as above 6,000 RPM, not 4,000 RPM

87. Two technicians are explaining on-board diagnostics (OBD) II diagnostics. Technician A says engine warm up cycles do NOT erase DTC's and freeze frame data. Technician B says OBD II requires that the diagnostic system, monitor all emission-related components and systems. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-B only b - Technician B is right because OBD II is designed to detect component degradation or faulty emission-related system that prevents compliance with federal emission standards. Regulations for OBD-II vehicles requires a computer to test for exhaust emissions within 1.5 times FTP limits and Flash the MIL (Malfunction Indicator Lamp) if engine misfire could damage catalytic converter. Technician A is wrong because 50 warm-up cycles will erase DTCs and their associated freeze frames.

52. On a sequential fuel injected engine, the vacuum hose from the fuel-pressure regulator was removed from the regulator and gasoline came out of the hose. Technician A says it is a normal for droplets of gasoline to come out the fuel pressure regulator hose. Technician B says the pressure regulator diaphragm may be leaking causing the fuel to get into the hose. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-B only b - Technician B is right because if the pressure regulator diaphragm is leaking fuel will come out of the hose. Technician A is wrong because this is not a normal condition

69. Technician A says if the vacuum hose is removed from the fuel pressure regulator the fuel pressure should decrease. Technician B says there should never be any fuel present on the vacuum side of the regulator diaphragm. Who is right? a. A only b. B only c. Both A and B d. Neither A nor B

-B only b - Technician B is right because if there is fuel on the vacuum side of the fuel pressure regulator, the diaphragm is leaking and defective. Technician A is wrong because if the vacuum hose is removed from the fuel pressure regulator the fuel pressure should increase not decrease

57. With the ignition key on and engine off, the above mass air flow sensor voltage readings are found. What do these readings indicate? a. Normal circuit values b. Defective MAF sensor c. Bad ground d. High battery voltage

-Bad Ground c - Composite vehicle electrical diagram 2 of 4 (pin B) on page 31 of the Composite Vehicle Type 4 should be 0.5 volts or less to indicate a good sensor ground. The other three choices show normal voltage values for KOEO (ignition key on and engine off).

76. A vehicle comes in with the MIL (malfunction indicator light) on with DTC (Diagnostic Trouble Code) P0456 (small leak detected in EVAP canister system). Technician A says a defective vent solenoid or a leak could be the cause. Technician B says a wrong or defective gas cap could be the cause. Who is right a. A only b. B only c. Both A and B d. Neither A nor B

-Both A and B c - Both technicians are right because DTC (Diagnostic Trouble Code) P0456 (small leak detected in EVAP canister system) is caused by the following: defective vent or purge solenoid, leak in the EVAP hoses or a defective, loose or wrong gas cap.

56. The VVT (variable valve timing) on the composite vehicle has set the diagnostic trouble code P1349 for a VVT system malfunction and will not start. Which of the following is the MOST likely cause? a. One CMP (Camshaft Position) sensor have failed b. Both CMP sensors have failed c. The CKP (Crankshaft position sensor) has failed d. Open circuit at ECM pin #204

-Both CMP sensors have failed b - Page 12 of the Composite Vehicle Type 4 states that when the CMP (Camshaft Position) sensor signals are not detected during cranking, the engine control module stores a DTC and results in a No-start condition. Answer A is wrong because the failure of only one CMP signal will set the DTC and the valve timing will default to the fully retarded position but the engine will still start, (see page 12 of the Composite Vehicle Type 4). Answer C is wrong because a failure of the CKP (crankshaft position sensor) will cause a no-start but it will not set the DTC P1349 for a VVT system malfunction. Answer D is wrong because an open in this circuit will affect the operation of the Bank 2 Camshaft Position Actuator Control Solenoid and set the DTC P1349 for a VVT system malfunction but will not result in a No-start condition (see page 32 of the Composite Vehicle Type 4).

64. This question has the word EXCEPT. For this question, look for the choice that could NOT meet the described situation. Read the entire question carefully before choosing your answer. If a return-less fuel system pressure gauge reading is out of specification, you do all of the following, EXCEPT: a. Check fuel pump relay b. Check fuel hoses and fuel tubes for clogging c. Check fuel filter d. Check fuel pressure regulator for clogging

-Check fuel pump relay a - Check fuel pump relay is the exception because as part of this procedure you read the indication of fuel pressure on the gauge, so the fuel pump relay must be working if there is pressure available on the gauge and there is no need to check the fuel pump relay.

84. As the efficiency of the catalytic converter drops through deterioration, the switching rate of the rear O2 (oxygen) ½ sensor signal will start to look like the front O2 sensor signal. When the rear O2 sensor signal reaches approximately 75% of the front O2 sensor, which of the following happens? a. DTC is stored and MIL is on b. One-trip flag is set with a code stored but the MIL is not on c. Replace the catalytic converter d. Change the catalyst beads in the converter

-DTC is stored and MIL is on. a - As the efficiency of the catalytic converter drops from deterioration, the switching rate of the rear O2 sensor signal will start to look like the front O2 sensor signal. When the rear O2 sensor signal reaches approximately 75% of the front O2 sensor signal, a Diagnostic Trouble Code (DTC) will be stored and the MIL will come on.

85. A scan tool check of the canister purge valve control solenoid shows it is always open. Which of the following could be the cause? a. Vacuum source problem b. Vacuum passage restriction c. Broken purge valve vacuum diaphragm d. Defective ECM (Engine Control Module)

-Defective ECM (Engine Control Module) d - A faulty ECM (Engine Control Module) can cause a purge valve control solenoid to be always open. A is wrong because the purge valve control solenoid is not vacuum controlled. B is wrong because the purge valve control solenoid is not vacuum controlled. C is wrong because a diaphragm is not used in the purge valve control solenoid.

58. With the ignition key on and engine off, the above manifold absolute pressure sensor voltage readings are found. What do these readings indicate? a. Normal circuit values b. Defective MAP sensor c. Bad ground d. High V-ref

-Defective Map sensor b - Composite vehicle electrical diagram 2 of 4 on page 31 of the Composite Vehicle Type 4, PIN C, which is MAP sensor output, should be 4.5 volts at closed throttle engine off with zero engine vacuum to indicate a good sensor. The other three choices show normal voltage values for KOEO (ignition key on and engine off). See page 15 of the Composite Vehicle.

77. A vehicle comes in with the malfunction indicator light on with a P0455 (small leak detected in EVAP canister system) DTC (Diagnostic Trouble Code) stored. Which of the following could be the cause? a. Defective PCM b. Defective purge (vent) solenoid c. High fuel pressure d. Secondary air injection system

-Defective Purge (vent) solenoid b - A defective purge or vent solenoid is one of four possible causes for a P0455 DTC. The others (defective or loose fuel cap, EVAP canister broken or hose cracked or loose, or engine vacuum leak) are not listed.

73. This scan data was retrieved from a vehicle that had two stored diagnostic trouble codes (DTCs) for low HO2S (Heated Oxygen Sensor) voltage on sensors 1/1 and 2/1 (Banks 1 & 2) and two stored DTCs for the mixture being too rich. What is the MOST likely cause based on the scan data? a. Defective fuel pump b. Partially clogged EVAP canister purge solenoid c. Partially clogged EGR ports d. Defective MAF (Mass Air Flow) sensor

-Defective fuel pump a - Defective fuel pump is correct because the fuel monitor will set a DTC if the long term fuel trim is negative at -30% indicting fuel being reduced to a rich condition. The only fuel system component listed is the fuel pump. Additionally, the fuel pressure is shown as at 90 psi, when only calling for 50% duty cycle (see pages 5 and 14 of the composite). Both Air/Fuel Ratio Sensors have set DTCs and both are showing low voltage indicating a rich condition. Answers B and C are wrong because the data stream shows normal readings and D is wrong because the MAF readings are normal.

60. This question has the word EXCEPT. For this question, look for the choice that would not meet the described situation. Read the entire question carefully before choosing your answer. Using the above engine data stream, all of the following components or systems are malfunctioning, EXCEPT: a. Fuel pump b. EGR system c. Loss of fuel control d. Rich mixture

-EGR system b - EGR system is the exception because the EGR valve position sensor is indicating the correct voltage value for 75% throttle (see page 16 of composite vehicle). Answers A, C and D are wrong: the fuel pump is malfunctioning because the fuel monitor will set DTCs if the long term fuel trim is excessively high at +36% indicating loss of fuel control and the fuel pump is the most likely cause to the LEAN reading of both AFRS (Air/Fuel Ratio Sensors). Both oxygen sensors have set DTCs and both are showing low voltage indicating high oxygen in the exhaust stream, which is a rich condition because only oxygen is sensed in the exhaust stream.

82. A scan tool is being used to evaluate the overall EGR system operation on a vacuum-type EGR system. Which of the following is the best parameter to monitor? a. EGR valve operation during acceleration b. EGR temperature sensor voltage during part-throttle c. EGR valve operation during deceleration d. EGR valve operation at idle

-EGR temperature sensor voltage during part-throttle b - On systems that use manifold vacuum, the EGR solenoid valve is commanded ON during part-throttle conditions and moderate load.

65. A vehicle is being tested for exhaust emissions using a 5-gas analyzer. The test results show high O2 (oxygen) reading of 3.5% with HC of 90 ppm [parts per million] and a CO reading of 0.80%. Which of these is the MOST likely cause? a. Lean air/fuel mixture b. Rich air/fuel mixture c. Exhaust leak d. Defective spark plug

-Exhaust Leak c - Exhaust leak is right because an exhaust system leak can cause a vehicle to have a high O2 (oxygen) reading of 3.5% with normal HC and CO readings (HC = 90 ppm and CO = 0.80%). While O2 readings alone can generally be a good indicator of lean air/fuel mixtures, it is a good idea to compare it with the other exhaust gases as well. By comparing the readings, you will be less likely to chase a lean air/fuel mixture problem that in reality is only a leaking.

54. On the composite vehicle, both APP (Acceleration Pedal Position) sensors have failed and set multiple diagnostic trouble codes. Which of the following also takes place when these failures occur? a. TAC scan tool reading will be 16% b. Maximum throttle opening will be 30% c. Fast idle will be 1450 RPM d. Fast idle will set at 900 RPM

-Fast idle will set a 900 RPM c - Page 6 of the composite vehicle type 4 states that when both APP (Acceleration Pedal Position) sensors fail the engine control module (ECM) will turn on the MIL (Malfunction Indicator Lamp) and limit the maximum throttle opening to 35%, making choice "b" wrong and the fast idle speed will be 14001500 RPM. Answer option A is wrong because page 6 also states that when the TAC (Throttle Actuator Control) is disabled by the ECM after the failure of both APP sensors, the spring-loaded throttle plate will return to the default position of 15% throttle opening. Answer D is wrong because page 6 also states that, during this type of failure, the fast idle speed will be 1400-1500 RPM, not 900, which is the normal no load idle range of 850-900 RPM at 15% throttle opening.

53. The fuel pressure on a sequential fuel injected engine is being checked. Which of the following is done first? a. Connect the fuel pressure gauge b. Remove the fuel pump fuse c. Look up the procedure d. Release the fuel pressure

-Look up the procedure c - Before working on any vehicle, you must check the manufacturer's procedure. This is the first step. You need to know fuel pressure specifications and the steps of the procedure, especially if you have never done it before. On some vehicles, you may need to remove EFI fuse on others you release the pressure first.

66. Which of the following takes place when the fuel filter is installed backwards? a. No change b. Reduced fuel economy c. Lower power under load d. Fuel system pulsation noises

-Lower power under load c - Lower power under load is right because if the filter is installed in reverse, the flow is restricted. So, when there is a high demand, such as under load, the fuel required for higher power will not be available.

51. This question uses the word LEAST. For this question, look for the choice that would LEAST LIKELY fit the described situation. Read the entire question carefully before choosing your answer. A customer complained that the engine has spark knock or detonation during rapid acceleration or when driving up a hill. Which of the following is the LEAST likely cause? a. Missing air cleaner cold air hose b. Carbon buildup in the combustion chambers c. Lack of sufficient exhaust gas recirculation (EGR) flow d. Pinched or restricted fuel return line

-Pinched or restricted fuel return line d - Pinched or restricted fuel return line is the LEAST likely cause for spark knock or detonation because it is a fuel related issue and will not cause a lean condition, which is a fuel related cause for detonation. The other three choices can all cause detonation or spark knock.

68. What service task is being shown in the photo? a. Removing a fuel line b. Installing fuel filter c. Checking fuel pressure d. Removing fuel filter

-Removing fuel line a - The photo shows the use of a white plastic insert tool to release the internal line lock

62. A technician is using an original equipment manufacturer bi-directional scan tool to test the fuel pump relay. The scan tool will command the PCM (powertrain control module) or ECM (engine control module) to turn on the fuel pump relay so the pump will run continuously. If the pump cannot be heard running, which of the following is the next step? a. Replace the fuel pump relay b. Replace the fuel pump c. Squeeze the fuel pump supply line d. Replace the fuel pump supply line

-Squeeze the fuel pump supply line. c - The scan tool will instruct the PCM or ECM to energize the fuel pump relay so the pump will run continuously. If you cannot hear the fuel pump, the next step is to squeeze the fuel pump supply line to see if you can feel pressure. If you do not feel pressure, the fuel pump is not operating

55. The composite vehicle has set a misfire diagnostic trouble code (DTC) P0303 for #3 cylinder along with DTC P0300. A technician finds that the injector has failed but is still receiving system voltage. Which of the following should be checked? a. Voltage drop of injector at ECM Pin 122 b. Voltage check at ignition power feed c. Fuel Pump relay d. Continuity check between the fuse #4 and injectors

-Voltage drop of injector at ECM pin 122 a - Most likely the ECM (Engine Control Module) cannot ground the injector, so you do a voltage drop of the ground side of the injector, which is not contributing. The control systems relay provides 12 volts DC power through fuse #4 to the positive side of the fuel injectors. The ground to operate each injector is furnished by the ECM. You place the DMM red lead at the pin B of the injector and if the voltage does not drop, the circuit is open. Answer B is wrong because the ignition power feed would affect all systems. Answer C is wrong because the fuel pump relay does not supply voltage to the injectors. Answer D is wrong because if fuse #4 were open the engine would not run.

80. Which of the following would indicate a closed EGR (Exhaust Gas Recirculation) valve? a. Rough idle b. Stalling c. Spark knock d. Engine surge

-spark knock c - A spark knock is a symptom of an EGR valve that is always closed. The other choices are wrong because they are symptoms of an EGR valve that is always open

83. Which of the following is a prime source of problems in secondary air systems? a. Water b. Dirt c. Engine oil d. Engine coolant

-water a - Water is one of the prime sources of problems in these systems. There are two typical causes of water contamination. The first cause is failure of the reed valve to seal due to breakage or loss of temper, allowing water from the exhaust to enter the A.I.V. case. Second, the reed valves can also stick closed, preventing air from getting to the catalyst.