Question 1

Mode 6 data are the results of the monitor diagnostic tests.

Accepted Answer

Mode 6 data is the result of the monitor diagnostic tests.

Question 2

A technician is setting up a lab scope to measure a sensor. Technician A says that the vertical voltage scale must be adjusted in relation to the expected voltage signal. Technician B says the trigger slope must be set to positive if the trace begins with a rising voltage. Who is correct?
A) A only
B) B only
C) both A and B
D) neither A nor B

Accepted Answer

Technician A is correct because adjusting the vertical voltage scale is necessary to properly view the expected voltage signal. Technician B is also correct because setting the trigger slope to positive is appropriate when the trace begins with a rising voltage.

Question 3

Which statement is NOT true?
A) Some sensors are voltage or frequency generators
B) Some sensors are variable resistors
C) Some sensors are simple on-off switches
D) Some sensors are solenoids

Accepted Answer

Solenoids are actuators that convert electrical energy into mechanical energy. They are not sensors. A, B, and C are all true statements about sensors.

Question 4

A vehicle with a DTC for an engine coolant temperature out of range code is being tested. The serial data stream shows the coolant temperature to be 198 degrees Fahrenheit. When the technician tests the resistance between the ETC terminals, he finds infinite resistance. The specifications call for 20 to 40 ohms at 200 degrees Fahrenheit. After the ECT is replaced and the code is erased, the system runs normally and the code and MIL illumination do not reoccur. How is this possible?
A) There was excessive air in the cooling system; when the ECT sensor was removed, the trapped air bled out
B) The ETC code was set by a loose connection where the harness meets the ECT terminals; disconnecting and reconnecting the plug essentially fixed the problem
C) The problem is an intermittent electrical fault; it will eventually reoccur
D) When the ECT failed, the PCM substituted a nominal ECT value that allowed the engine to run in limp home mode; the substituted value was displayed by the scan tool

Accepted Answer

The PCM substituted a nominal value for the engine coolant temperature (ECT) when the sensor failed, which is why the scan tool displayed a temperature of 198 degrees Fahrenheit despite the sensor having infinite resistance, indicating it was faulty. This substitution allowed the engine to continue operating in a "limp home" mode until the issue was resolved.

Question 5

The resistance of the intake air temperature (IAT) sensor increases as air temperature increases.

Accepted Answer

The resistance of the IAT sensor decreases as air temperature increases; it's a negative temperature coefficient (NTC) thermistor.

Question 6

Trouble codes are being discussed. Technician A says that the first time the system detects a fault, a pending code is set. Technician B says that a pending code will turn on the MIL light. Who is correct?
A) A only
B) B only
C) both A and B
D) neither A nor B

Accepted Answer

Technician A is correct. When a fault is first detected, a pending code is set but the MIL light is not turned on. The code will only turn on the MIL light if the same fault is detected during subsequent driving cycles. Technician B is incorrect in saying that a pending code will turn on the MIL light.

Question 7

For most actuators, the circuit driver in the PCM applies a ground to the circuit to turn the actuator on and removes the ground to turn the actuator off.

Accepted Answer

This is the typical operation for most actuators controlled by the PCM circuit driver.

Question 8

A sensor with a bad ground connection will produce a lower than normal signal voltage.

Accepted Answer

The answer of A sensor with a bad ground connection...

Question 9

If the MIL light is ON, there will be a DTC and associated freeze frame data stored in the PCM's memory.

Accepted Answer

When the MIL light is illuminated, it means that there is an issue detected by one of the sensors or systems in the vehicle. This issue will trigger a Diagnostic Trouble Code (DTC) to be stored in the PCM's memory, along with associated freeze frame data that provides additional information about the conditions at the time the fault was detected.

Question 10

Which of the following tools is NOT used in testing engine sensors?
A) DMM
B) test light
C) scan tool
D) lab scope

Accepted Answer

A test light can potentially damage certain engine sensors, so it is not typically used in testing them. Instead, a DMM (Digital Multimeter), scan tool, and lab scope are commonly used for testing engine sensors.

Question 11

The sensor and output status data stored when a DTC is set is called ______.
A) snap shot data
B) freeze frame data
C) mode 6 data
D) failure record

Accepted Answer

The data stored when a DTC is set is called freeze frame data. This includes the sensor and output status at the time the code was set, allowing for easier diagnosis and troubleshooting of the issue.

Question 12

Because air/fuel ratio sensors produce a signal only after their current output has been processed by the PCM, they cannot be tested with a voltmeter or lab scope.

Accepted Answer

The answer of Because air/fuel ratio sensors produce a signal...

Question 13

On some vehicles, actuators can be tested with a scan tool by accessing output state control (OSC) or output test mode (OTM). In this mode, the actuator enabled or disabled, or the duty cycle increased or decreased.

Accepted Answer

Scan tools can communicate with a vehicle's onboard computer to test actuators by enabling or disabling them or adjusting their duty cycle through OSC or OTM.

Question 14

The engine coolant temperature sensor is typically found in the radiator.

Accepted Answer

The engine coolant temperature sensor is typically found on or near the engine block, cylinder head, or thermostat housing, not in the radiator.

Question 15

The device that protects the PCM and other electronic components from the voltage spike created in the windings of a solenoid, relay, or magnetic clutch when they are turned off is called a ______.
A) filter choke
B) clamping diode
C) suppression capacitor
D) voltage divider

Accepted Answer

A clamping diode, also known as a flyback diode or freewheeling diode, is used to protect electronic components from voltage spikes created when a solenoid, relay, or magnetic clutch is turned off. The diode provides a path for the current generated by the collapsing magnetic field, preventing it from damaging the PCM or other components. A filter choke, suppression capacitor, and voltage divider are not specifically designed for this purpose.

Question 16

Some PCM inputs come from another control module through the vehicle network.

Accepted Answer

This is true as some vehicle systems are interconnected through a network and can send information to the PCM.

Question 17

A vehicle towed into the shop with a "cranks but doesn't start" problem. A quick check under the hood reveals that the spark plugs are not firing and the injectors are not receiving a pulse from the PCM. The technician notices that the MIL light does not come on when the key is turned to the run position. What would you do next?
A) Check the PCM's fuses, power wires, and ground wires
B) Replace the PCM
C) Check the main power relay in the power distribution center
D) Check for codes with a scan tool

Accepted Answer

The MIL light not coming on suggests a power issue to the PCM. Checking the PCM's fuses, power wires, and ground wires is a logical first step to ensure the PCM is receiving power.

Question 18

Two technicians are discussing OBD-II monitor readiness status. Technician A says that the vehicle must be driven through a drive cycle that includes several minutes of idle, low-speed cruise, medium-speed cruise, and deceleration before all monitors can be performed. Technician B says all monitors can be performed in five minutes of fast idling. Who is correct?
A) A only
B) B only
C) both A and B
D) neither A nor B

Accepted Answer

Technician A is correct. Different monitors require different driving conditions to complete their self-tests. A drive cycle usually consists of a variety of operating situations including cold start, warm-up, steady speeds, acceleration, deceleration, and so on. The OBD-II system requires that these self-tests be completed to make sure the emissions control system is functioning correctly. Fast idling is not an adequate way to perform all the necessary self-tests for all monitors.

Question 19

The MAP sensor used on a turbocharged engine is calibrated the same as a MAP sensor for a nonturbocharged engine.

Accepted Answer

The MAP sensor used on a turbocharged engine is calibrated differently than a MAP sensor for a nonturbocharged engine because the pressure values measured by the sensor are different due to the presence of a turbocharger.

Question 20

A misfiring spark plug can cause a false oxygen sensor reading.

Accepted Answer

A misfiring spark plug can cause unburned fuel to enter the exhaust system, leading to a false reading from the oxygen sensor. This can result in decreased fuel efficiency and increased emissions.

Quiz 25: Detailed Diagnosis and Sensors

Mode 6 data are the results of the monitor diagnostic tests.

A technician is setting up a lab scope to measure a sensor. Technician A says that the vertical voltage scale must be adjusted in relation to the expected voltage signal. Technician B says the trigger slope must be set to positive if the trace begins with a rising voltage. Who is correct?

Which statement is NOT true?