Deck 12: General Motors Computerized Engine Controls

Question 1

The EONV (engine off natural vacuum)test is being discussed. Technician A says that to perform it, the PCM is kept powered for up to 4 minutes after the ignition switch is turned off. Technician B says that the natural vacuum created in the fuel tank as the engine cools, is from about 3 inches to about 5 inches of water.  Who is correct?

A)Technician A only
B)Technician B only
C)Both A and B
D)Neither A nor B

Answer 1

B

Question 2

Many GM systems place a PCM-generated signal, known as a bias voltage , on the oxygen sensor signal until it begins to generate its own voltage. The value of this bias voltage is:

A)45 mV
B)450 mV
C)4.5 V
D)5 V

Answer 2

B

Question 3

MAF sensors are being discussed. Technician A says to use a DC Voltmeter to measure the sensors output. Technician B says to use a Hertz meter to measure the sensors output. Who is correct?

A)Technician A only
B)Technician B only
C)Both A and B
D)Neither A nor B

Answer 3

B

Question 4

The idle air control (IAC)assembly on a GM TBI or PFI system is a/an _______________.

A)Stepper motor
B)Stepper solenoid
C)AC motor
D)Permanent magnet motor

Question 5

GM engines include a feature, called the engine metal overtemp mode , whereby at temperatures above _____ the PCM will selectively disable half of the cylinders at a time on a V6 or V8 engine to keep the engine temperature from reaching destructive levels.

A)70ºF
B)170ºF
C)270ºF
D)370ºF

Question 6

Technician A says a Central Multiport Fuel Injection (CMFI)system pulses all injectors simultaneously. Technician B says a sequential fuel injection (SFI)system pulses each injector individually. Who is correct?

A)Technician A only
B)Technician B only
C)Both A and B
D)Neither A nor B

Question 7

In modern GM engines, what type of sensor is the throttle position sensor (TPS)?

A)Thermistor
B)Hall effect sensors
C)Rheostat
D)Potentiometer

Question 8

Distributors are no longer needed because of many advances in technology. What is NOT one of these?

A)Spark advance can be controlled by a computer.
B)Tach reference signals can be taken directly from the crankshaft.
C)Camshaft position sensors can control simple vacuum advance spark systems.
D)Spark timing can be made permanently fixed.

Question 9

The PCM may turn the A/C clutch on or off in all of the following situations EXCEPT :

A)during WOT operation
B)if power steering pressure exceeds a specified value during idle
C)when the electric cooling fan is turned on
D)when the A/C control switch is turned on

Question 10

A GM vehicle with high idle speed is being diagnosed. Technician A says if the IAC counts show a value of 0, a vacuum leak is a possible cause. Technician B says if the IAC counts show a value of 0, the PCM may not be able to control the IAC. Who is correct?

A)Technician A only
B)Technician B only
C)Both A and B
D)Neither A nor B

Question 11

Which statement about the engine coolant temperature sensor is true?

A)Its resistance increases as the temperature decreases
B)Its resistance increases as the temperature increases
C)It is a PTC thermistor
D)Both A and C are correct

Question 12

The assembly line  data link connector (ALDL)on a non-OBDII vehicle has _______ terminals.

A)Sixteen
B)Fourteen
C)Twelve
D)Ten

Question 13

Ordinary engine noise, known as background noise, can be used to allow the PCM to detect some circuit faults. The sensor used to detect the engine noise is the:

A)TPS
B)KS
C)MAP sensor
D)ECT sensor

Question 14

The system that allows GM to retrieve vehicle diagnostic reports via satellite is called:

A)OnStar
B)Cadillac User Experience (CUE)
C)GM navigational system
D)GM Multiplexing

Question 15

A V8 engine equipped with waste spark ignition has how many coils?

A)Eight
B)Four
C)Two
D)One

Question 16

On a GM vehicle, in order to properly control the air/fuel ratio during cranking mode the PCM relies primarily on information from which of the following sensors?

A)O₂S and TPS
B)MAP/MAF sensor and TPS
C)ECT sensor and TPS
D)IAT sensor and TPS

Question 17

TPS adjustment is being discussed. Technician A says all PFI systems are adjustable. Technician B says that performing a correction of the minimum idle speed adjustment is cause to perform a TPS adjustment. Who is correct?

A)Technician A only
B)Technician B only
C)Both A and B
D)Neither A nor B

Question 18

In order to make accurate measurements of reference voltages, the voltmeter must have an input impedance of at least:

A)100 Ω
B)1 MΩ
C)10 MΩ
D)100 MΩ

Question 19

Pressure sensors are being discussed. Technician A says GM fuel injected vehicles use a separate sensor to measure barometric pressure. Technician B says the MAP sensor operates on a 5 volt reference. Who is correct?

A)Technician A only
B)Technician B only
C)Both A and B
D)Neither A nor B

Question 20

The body control module (BCM)is being discussed. Technician A says it is a microcomputer with about the same computer power as the PCM. Technician B says it is a microcomputer that exchanges information with the PCM. Who is correct?

A)Technician A only
B)Technician B only
C)Both A and B
D)Neither A nor B