Electrical II and HVAC Automotive

How does a typical NTC temperature sensor work?

It has a special resistor (thermistor) that increases the resistance when cold and decreases the resistance when hot.

What is the difference between a positive trigger and a negative trigger?

Positive is when the voltage rises above a set point while negative is when it falls below a set point

What is the difference between an oscilloscope and a graphing multimeter?

Scopes display the voltage directly and are faster where as GMM just shows the reading of the meter on the graph.

If the transmission fluid temperature (TFT) sensor were to fail open (as if it were unplugged), what would the PCM do to the transmission shifting points?

Shift points delayed.

Why are DC signals that change called pulse trains?

They are called pulse trains because of the way they look on the scope when being displayed.

A P0118 DTC is being discussed. Technician A says that the ECT sensor could be shorted internally. Technician B says that the signal wire could be open. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

B. Tech B

A high O2S voltage could be due to _______. A. A rich exhaust B. A lean exhaust C. A defective spark plug wire D. Both a and c

A. A rich exhaust

Which air flow sensor has a dampening chamber? A. A vane air flow B. A hot film MAF C.A hot wire MAF D. A karman Vortex

A. A vane air flow

Typical TP sensor voltage at idle is about ______. A. 2.50 to 2.80 volts B. 0.3 volt to 1.2 volts C. 1.5 to 2.8 volts D. 13.5 to 15.0 volts

B. 0.3 to 1.2 volts

Voltage signals (waveforms) that do not go below zero are called ______. A. AC signals B. Pulse trains C. Pulse-width D. DC coupled signals

B. Pulse trains

Which wire on a TP sensor should be back-probed to check the voltage signal to the PCM? A. 5-volt reference (Vref) B. Signal C. Ground D. Meter should be connected between the 5-volt reference and the ground

B. Signal

A fuel-injection system that does not use a sensor to measure the amount (or mass) of air entering the engine is usually called a(n) _______ type of system. A. Air vane-controlled B. Speed density C. Mass air flow D. Hot wire

B. Speed density

What is the purpose of each of the three wires on a typical TP sensor?

- A 5-volt reference (Vref) - Low reference - Signal wire

List four PCM output devices?

- Fuel injectors - Ignition timing advance - Fuel pump relay - AC compressor relay - Cooling fan relay - EGR solenoid/cam phasers - Electronic Throttle Control motor - Idle Air Control Motor/Solenoid - Transmission shift and Torque converter solenoids - Instrument cluster MIL

List four inputs to the PCM?

- Oxygen sensor - Throttle position sensor - Vehicle speed sensor - Manifold absolute pressure sensor - Mass airflow sensor - Intake air temperature sensor - Engine coolant temperature sensor - Camshaft position sensor - Crankshaft position sensor

What ALL does the PCM do with the TP sensor signal voltage?

- Senses driver demand - Target idle speed - Clear flood mode - Rationality testing for MAP or MAF sensors - air conditioning compressor operation - automatic transmission shift points - Torque converter clutch engagement and release

Which statement is false? A. Absolute pressure is equal to barometric pressure plus intake manifold vacuum. B. A decrease in manifold vacuum means an increase in manifold pressure. C. The MAP sensor compares manifold vacuum to a perfect vacuum. D. Barometric pressure minus the MAP sensor reading equals intake manifold vacuum.

A. Absolute pressure is equal to barometric pressure plus intake manifold vacuum.

When measuring the output signal of a MAP sensor on a General Motors vehicle, the digital Multimeter should be set to read _____. A. DC V B. AC V C. Hz D. DC A

A. DC V

As the percentage of antifreeze in the coolant increases, ________. A. The freeze point decreases (up to a point) B. The boiling point decreases C. The heat transfer increases D. All of the above

A. Freeze point decreases (up to a point)

Cycles per second are expressed in _______. A. Hertz B. Duty cycle C. Pulse width D. Slope

A. Hertz

Which type of sensor uses a burn-off circuit? A. Hot wire MAF sensor B. Hot firm MAF sensor C. Vane-type air flow sensor D. Both a and b

A. Hot wire MAF sensor

As the load on an engine increases, the manifold vacuum decreases and the manifold absolute pressure ______. A. Increases B. Decreases C. Changes with barometric pressure only (altitude or weather) D. Remains constant (absolute)

A. Increases

What happens to the voltage measured at the ECT sensor when the thermostat opens? A. Increases slightly B. Increases about 1 volt C. Decreases slightly D. Decreases about 1 volt

A. Increases slightly

The SAE term for the vehicle computer is _____. A. PCM B. ECM C. ECA D. Controller

A. PCM

A signal showing the voltage of a battery displayed on a digital storage oscilloscope (DSO) is being discussed. Technician A says that the display will show one horizontal line above the zero line. Technician B says that the display will show a line sloping upward from zero to the battery voltage level. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

A. Tech A

An oxygen sensor is being tested with a digital Multimeter (DMM), using the MIN/MAX function. The readings are: minimum = 78 mV; maximum = 932 mV; average = 442 mV. Technician A says that the engine is operating correctly. Technician B says that the oxygen sensor is skewed too rich. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

A. Tech A

Technician A says that MAP sensors use a 5-volt reference voltage from the PCM. Technician B says that the MAP sensor voltage will be higher at idle at high altitudes compared to when the engine is operating at near sea level. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

A. Tech A

Two technicians are diagnosing a poorly running engine. There are no diagnostic trouble codes. When the MAF sensor is unplugged, the engine runs better. Technician A says that this means that the MAF is supplying incorrect air flow information to the PCM. Technician B says that this indicates that the PCM is defective. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

A. Tech A

Two technicians are discussing the DC coupling setting on a DSO. Technician A says that the position allows both the DC and AC signals of the waveform to be displayed. Technician B says that this setting allows just the DC part of the waveform to be displayed. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

A. Tech A

After a TP sensor has been tested using the MIN/MAX function on a DMM, a reading of zero volts is displayed. What does this reading indicate? A. The TP sensor is open at one point during the test B. The TP sensor is shorted C. The TP sensor signal is shorted to 5-volt reference (Vref) D. Both b and c are possible

A. The TP sensor is open at one point during the test

Which sensor may have a switch that controls the electric fuel pump? A. VAF B. Hot wire MAF C.Hot folter MAF D. Karman Vortex sensor

A. VAF

What unit of electricity is used as a signal for a computer? A. Volts B. Ohms C. Amperes D. Watts

A. Volts

A throttle position sensor waveform is going to be observed. At what preferred setting should the volts per division be set to see the entire waveform from 0 to 5 volts? A. 0.5 V/division B. 1.0 V/division C. 2.0 V/division D. 5.0 V/division

B. 1.0 V/division

The typical MAF reading on a scan tool with the engine at idle speed and normal operating temperature is ______. A. 1 to 3 grams per second B. 3 to 7 grams per second C. 8 to 12 grams per second D. 14 to 24 grams per second

B. 3 to 7 grams per second

A typical GM IAT or ECT sensor reads about 3,000 ohms when tested using a DMM. This resistance represents a temperature of about ________. A. -40*F (-40*C) B. 70*F (20*C) C. 120*F (50*C) D. 284*F (140*C)

B. 70F (20*C)

A typical MAP compares the vacuum in the intake manifold to ______. A. Atmosphere pressure B. A perfect vacuum C.Barometric pressure D. The value of the IAT sensor

B. A perfect vacuum

Computer speed is measured in _____. A. Baud rate B. Clock speed (Hz) C. Voltage D. Bytes

B. Clock speed (Hz)

When testing an ECT sensor on a vehicle, a digital Multimeter can be used and the signal wires back probed. What setting should the technician use to test the sensor? A. AC volts B. DC volts C. Ohms D. Hz (Hertz)

B. DC Volts

The sensor that most determines fuel delivery when a fuel-injected engine is first started is the _____. A. O2 Sensor B. ECT sensor C. Engine MAP sensor D. IAT sensor

B. ECT sensor

The four basic automotive computer functions include _______. A. Writing, processing, printing, and remembering. B. Input, processing, storage, and output. C. Data gathering, processing, output, and evaluation D.

B. Input, Processing, storage, and output.

Wich is not a purpose or function of the PCM's MAP sensor circuitry? A. Senses the load on the engine B. Measures engine speed C. Calculates fuel delivery based on altitude D. Helps diagnose the EGR system

B. Measures engine speed

Technician A says an analog scope can store the waveform for viewing later. Technician B says that the trigger level has to be set on most scopes to be able to view a changing waveform. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

B. Tech B

Two technicians are discussing a stepped ECT circuit. Technician A says that the sensor used for a stepped circuit is different than one used in a non-stepped circuit. Technician B says that a stepped ECT circuit uses different internal resistance inside the PCM. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

B. Tech B

Two technicians are discussing the IAT sensor. Technician A says that the IAT sensor is more important to the operation of the engine (higher authority) than the ECT sensor. Technician B says that the PCM will add fuel if the IAT indicates that the incoming air temperature is cold. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

B. Tech B

What two things can a vehicle computer actually perform (output)? A. Store and process information. B. Turn something on or turn something off. C. Calculate and vary temperature. D. Control fuel and timing only.

B. Turn something on or turn something off.

An engine fuel temp (EFT) sensor is used on some vehicles, since fuel temperature changes the ______________ of the fuel. A. color B. density C. octane rating D. Pressure

B. density

An Oscilloscope display is called a ______. A. grid B. graticule C. division D. box

B. graticule

A TP sensor is what type of sensor? A. Rheostat B. Voltage generating C. Potentiometer D. Piezoelectric

C. Potentiometer

Most TP sensors have how many wires A. 1 B. 2 C. 3 D. 4

C. 3

Analog signals from sensors are changed to digital signals for processing by the computer through which type of circuit? A. Digital B. Analog C. Analog-to-digital converter D. PROM

C. Analog-to-digital converter

A MAF sensor on a General Motors 3800 V-6 is being tested for contamination. Technician A says that the sensor should show over 100 grams per second on a scan tool display when the accelerator is depressed to WOT on a running engine. Technician B says that the output frequency should exceed 7000 Hz when the accelerator pedal is depressed to WOT on a running engine. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

C. Both Tech

A P0102 DTC is being discussed. Technician A says that a sensor circuit shorted-to-ground can be the cause. Technician B says that an open sensor voltage supply circuit could be the cause. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

C. Both Tech

A P0107 DTC is being discussed. Technician A says that a defective MAP sensor could be the cause. Technician B says that a MAP sensor signal wire shorted-to-ground could be the cause. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

C. Both Tech

Two technicians are discussing testing MAP sensors. Technician A says that voltage on a General Motors vehicle at idle should be about 1.0 volt. Technician B says MAP sensor frequency on a Ford vehicle at idle should be about 90-108 Hz. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

C. Both Tech

The "brain" of the computer is the ____. A. PROM B. RAM C. CPU D. AD converter

C. CPU

If the transmission fluid temperature (TFT) sensor indicates cold automatic transmission fluid temperature, what would the PCM do to the shifts? A. Normal shifts and normal operation of the torque converter clutch B. Disable torque converter clutch; normal shift points C. Delayed shift points and torque converter clutch may be disabled. D. Normal shifts but overdrive will be disabled

C. Delayed shift points and torque converter clutch may be disabled.

Air that enters the engine without passing through the air flow sensor is called ______. A. Bypass air B. Dirty air C. False air D. Measured air

C. False air

A digital meter that can show waveforms is called a _______. A. DVOM B. DMM C. GMM D. DSO

C. GMM

When testing the ECT sensor with the connector disconnected, the technician should select what position on the DMM? A. AC volts B. DC volts C. Ohms D. Hz (Hertz)

C. Ohms

The voltage output of a zirconia oxygen sensor when the exhaust stream is lean (excess oxygen) is ______. A. Relatively high (close to 1 volt) B. About in the middle of the voltage range C. Relatively low (close to 0 volt) D. Either a or b, depending on atmospheric pressure

C. Relatively low (close to 0 volt)

After a TP sensor has been tested using the MIN/MAX function on a DMM, a reading of 5 volts is displayed. What does this reading indicate? A.The TP sensor is open at one point during the test B. The TP sensor is grounded C. The TP sensor signal is shorted to 5-volt reference D. Both a and b are possible

C. The TP sensor signal is shorted to 5-volt reference

Which design of MAP sensor produces a frequency (digital) output signal? A. Silicon-diaphram strain gauge B. Piezo-resistivity design C. Variable Capacitor-capsule D. Ceramic disc

C. Variable Capacitor-capsule

When checking the ECT sensor with a scan tool, about what temperature should be displayed if the connector is removed from the sensor with the key on, engine off? A. 284*F (140*C) B. 230*F (110*C) C. 120*F (50*C) D. -40*F (-40*C)

D. -40*F (-40*C)

The frequency output of a digital MAP sensor is reading 114 Hz. What is the approximate engine vacuum? A. Zero B. 5 in. Hg C. 10 in. Hg D. 15 in. Hg

D. 15 in. Hg

Setting the time base to 50 ms per division will allow the technician to view a waveform how long in duration? A. 50 ms B. 200 ms C. 400 ms D. 500 ms

D. 500 ms

Which item is a computer input sensor? A. RPM B. Throttle position C. Engine coolant temperature D. All of the above

D. All of the above

Which item is a computer output device? A. Fuel Injector B. Transmission shift solenoid C. Evaporative emission control solenoid D. All of the above

D. All of the above

A P0122 DTC is retrieved using a scan tool. This DTC means ______. A. The TP sensor voltage is low B. The TP sensor could be shorted-to-ground C. The TP sensor signal circuit could be shorted-to-ground D. Any of the above could be correct

D. Any of the above could be correct

A low O2S voltage could be due to ______. A. A rich exhaust B. A lean exhaust C. A defective spark plug wire D. Both

D. Both b and c

Oscilloscopes use what type of lead connector? A. Banana plugs B. Double banana plugs C. Single conductor plugs D. Can be banana or BNC

D. Can be banana or BNC

An OBD II vehicles use what type of read-only memory? A. ROM B. PROM C. EPROM D. EEPROM

D. EEPROM

Which sensor does the TP sensor backup if the PCM determines that a failure has occurred? A. Oxygen sensor B. MAF sensor C. MAP sensor D. Either b or c

D. Either b or c

Coolant is water and _______. A. Methanol B. Glycerin C. Kerosene D. Ethylene glycol

D. Ethylene glycol

A technician attaches one lead of a digital voltmeter to the ground terminal of the TP sensor and the other meter lead to the negative terminal of the battery. The ignition is switched to on, engine off and the meter displays 37.3 mV. Technician A says that this is the signal voltage and is a little low. Technician B says that only the TP sensor ground circuit has excessive resistance. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither Tech

D. Neither Tech

Two technicians are discussing Karman Vortex sensors. Technician A says that they contain a burn-off circuit to keep them clean. Technician B says that they contain a movable vane. Which technician is correct? A. Tech A B. Tech B C. Both Tech D. Neither tech

D. Neither Tech

What type of sensor is used to measure the position of the throttle? A. Negative temperature coefficient (NTC) thermistor B. Positive temperature coefficient (NTC) thermistor C. Engine speed (RPM) D. Potentiometer

D. Potentiometer

What is the difference between DC coupling and AC coupling?

DC coupling displays both AC and DC voltage at the same time so you would be able to see an alternator at 14.4 volts and its displayed with the AC voltage on top of the DC so you can see if there is any AC voltage in the system when there shouldn't be.

What is the difference between volatile and nonvolatile RAM?

Nonvolatile RAM is information that is permanently stored even with the battery disconnected. This is used for the vehicle odometer for example. Volatile RAM memory is lost whenever the ignition is turned off. KAM can be used to store this info even if the ignition is turned off.