PATH:  Engine Performance & Emission Controls > Components & Systems > Accelerator Pedal Position Sensor > Testing

Testing

Animations and Tech Tips

Click to view: TPS voltage sweep

1. Backprobe with a high impedance voltmeter at APP sensor terminals G and A.

2. With the key ON and engine off, the voltmeter reading should be approximately 5.0 volts.

3. If the voltage is not as specified, either the wiring to the APP sensor or the ECM may be faulty. Correct any wiring or ECM faults before continuing test.

4. Backprobe with a high impedance voltmeter at terminals F and A.5. With the key ON and engine idling, the APP sensor voltage

should be approximately 0.5 volts.6. Verify that the APP voltage increases or decreases smoothly as

the throttle is opened or closed. Make sure to open and close the throttle very slowly in order to detect any abnormalities in the APP sensor voltage reading.

7. If the APP sensor voltage is not as specified, replace the APP sensor.

8. Backprobe with a high impedance voltmeter at APP sensor terminals D and B.

9. With the key ON and engine off, the voltmeter reading should be approximately 5.0 volts.

10. If the voltage is not as specified, either the wiring to the APP sensor or the ECM may be faulty. Correct any wiring or ECM faults before continuing test.

11. Backprobe with a high impedance voltmeter at terminals C and B.12. With the key ON and engine idling, the APP sensor voltage

should be approximately 4.5 volts.13. Verify that the APP voltage decreases smoothly as the throttle is

opened. Make sure to open and close the throttle very slowly in order to detect any abnormalities in the APP sensor voltage reading.

14. If the APP sensor voltage is not as specified, replace the APP sensor.

15. Backprobe with a high impedance voltmeter at APP sensor terminals E and J.

16. With the key ON and engine off, the voltmeter reading should be approximately 5.0 volts.

17. If the voltage is not as specified, either the wiring to the APP sensor or the ECM may be faulty. Correct any wiring or ECM faults before continuing test.

18. Backprobe with a high impedance voltmeter at terminals K and J.19. With the key ON and engine idling, the APP sensor voltage

should be approximately 4.0 volts.20. Verify that the APP voltage decreases smoothly to about 2.0 volts

as the throttle is opened. Make sure to open and close the throttle very slowly in order to detect any abnormalities in the APP sensor voltage reading.

21. If the APP sensor voltage is not as specified, replace the APP sensor module.

Accelerator Pedal Position (APP) sensor wiring diagram

Click to Enlarge PATH:  Engine Performance & Emission Controls > Components &

Systems > Camshaft Position Sensor > Testing Testing

Animations and Tech Tips

Click to view: TPS voltage sweep

Camshaft Position (CMP) sensor wiring schematic

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1. Disconnect the CMP sensor wiring harness and connect an LED test light between CMP harness terminal C and battery ground.

2. With the ignition ON and the engine off, verify that the test light illuminates.

3. If not as specified, repair or replace the fuse and/or wiring.4. Carefully connect the test light between CMP harness terminal A

and C and verify that the test light illuminates.5. If not as specified, repair the CMP harness ground circuit

(terminal A).6. Turn the ignition OFF and disconnect the test light.7. Next, connect suitable jumper wires between the CMP sensor and

CMP sensor harness. Connect a DC volt meter to the jumper wire corresponding to CMP terminal B and battery ground.

8. Start the engine and verify that the voltage signal is 5-7 volts.9. If it is not as specified, the CMP sensor may be faulty.

PATH:  Engine Performance & Emission Controls > Components & Systems > Crankshaft Position Sensor > Testing

Testing

Animations and Tech Tips

Click to view: TPS voltage sweep

1. Disconnect the CKP sensor harness. Connect an LED test light between battery ground and CKP harness terminal A.

2. With the ignition ON and the engine off, verify that the test light illuminates.

3. If not as specified, repair or replace the fuse and/or wiring.4. Carefully connect the test light between CKP harness terminal A

and B. Verify that the test light illuminates.

Crankshaft Position (CKP) sensor wiring diagram

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5. If not as specified, repair the CKP harness ground circuit (terminal B).

6. Turn the ignition OFF and disconnect the test light.7. Next, connect suitable jumper wires between the CKP sensor and

CKP sensor harness. Connect a duty cycle meter to the jumper wire corresponding to CKP terminal C and battery ground.

8. Crank the engine and verify that the duty cycle signal is between 40-60%.

9. If it is not as specified, the CKP sensor may be faulty.10. Next, connect a AC volt meter to the jumper wire corresponding

to CKP terminal C and battery ground.11. Crank the engine and verify that the AC voltage signal is at least

10.0 volts.12. If not as specified the CKP sensor may be faulty.1. Check the sensor wiring, the wiring harness and the terminals for

damage and repair as necessary.2. Disconnect the CKP sensor harness. Connect an Digital Volt Ohm

Meter (DVOM) attach the negative lead of the meter to battery ground and the positive lead to CKP harness terminal C. The voltage should be between 4.8-5.2 volts.

3. If not as specified, repair or replace the fuse and/or wiring.4. Connect an LED test light between the battery positive terminal

and CKP terminal B.5. With the ignition ON and the engine off, verify that the test light

illuminates.6. If not as specified, repair or replace the wiring.

Crankshaft Position (CKP) sensor wiring diagram-6.5L diesel engine

Click to Enlarge

7. Turn the ignition OFF and disconnect the test light.8. Next, connect suitable jumper wires between the CKP sensor and

CKP sensor harness. Connect a DVOM to the jumper wire corresponding to CKP terminal A and battery ground.

9. Crank the engine and verify that the voltage is 4 volts or more.10. If it is not as specified, the CKP sensor may be faulty.

PATH:  Engine Performance & Emission Controls > Components & Systems > Heated Oxygen Sensor > Testing

Testing

Animations and Tech Tips

Click to view: Testing an HO2S heater circuit

Click to view: A good heated oxygen sensor waveform

Click to view: Comparing heated oxygen sensor waveforms

1. Perform a visual inspection on the sensor as follows:1. Remove the sensor from the exhaust.

2. If the sensor tip has a black/sooty deposit, this may indicate a rich fuel mixture.

3. If the sensor tip has a white gritty deposit, this may indicate an internal anti-freeze leak.

4. If the sensor tip has a brown deposit, this could indicate oil consumption.

All these contaminates can destroy the sensor, if the problem is not repaired the new sensor will also be damaged.

2. Reinstall the sensor.3. Start the engine and bring it to normal operating temperature, then

run the engine above 1200 rpm for two minutes.4. Turn the ignition OFF disengage the H02S harness connector.5. Connect a test light between harness terminals A and B. With the

ignition switch ON and the engine off, verify that the test light is lit. If the test light is not lit, either the supply voltage to the H02S heater or the ground circuit of the H02S heater is faulty. Check the H02S wiring and the fuse.

6. Next, connect a high impedance ohmmeter between the H02S terminals B and A and verify that the resistance is 3.5-14.0 ohms.

7. If the H02S heater resistance is not as specified, the H02S may be faulty.

8. Start the engine and bring it to normal operating temperature, then run the engine above 1200 rpm for two minutes.

9. Backprobe with a high impedance averaging voltmeter (set to the DC voltage scale) between the oxygen sensor (02S) and battery ground.

10. Verify that the 02S voltage fluctuates rapidly between 0.40-0.60 volts.

11. If the 02S voltage is stabilized at the middle of the specified range (approximately 0.45-0.55 volts) or if the 02S voltage fluctuates very slowly between the specified range (02S signal crosses 0.5 volts less than 5 times in ten seconds), the 02S may be faulty.

12. If the 02S voltage stabilizes at either end of the specified range, the ECM is probably not able to compensate for a mechanical problem such as a vacuum leak or a faulty fuel pressure regulator. These types of mechanical problems will cause the 02S to sense a constant lean or constant rich mixture. The mechanical problem will first have to be repaired and then the 02S test repeated.

13. Pull a vacuum hose located after the throttle plate. Voltage should drop to approximately 0.12 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a lean mixture condition. Reattach the vacuum hose.

14. Richen the mixture using a propane enrichment tool. Voltage should rise to approximately 0.90 volts (while still fluctuating

rapidly). This tests the ability of the 02S to detect a rich mixture condition.

15. If the 02S voltage is above or below the specified range, the 02S and/or the O2S wiring may be faulty. Check the wiring for any breaks, repair as necessary and repeat the test.

Heated Oxygen Sensor (H02S) wiring diagram

Click to Enlarge PATH:  Engine Performance & Emission Controls > Components &

Systems > Intake Air Temperature Sensor > Testing Testing

  Description of the Intake Air Temperature sensor

1. Remove the Intake Air Temperature (IAT) sensor.2. Connect a digital ohmmeter to the two terminals of the sensor.3. Using a calibrated thermometer, compare the resistance of the

sensor to the temperature of the ambient air. Refer to the temperature vs. resistance illustration.

4. Repeat the test at two other temperature points, heating or cooling the air as necessary with a hair dryer or other suitable tool.

5. If the sensor does not meet specification, it must be replaced.

Intake Air Temperature (IAT) sensor wiring diagram

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Intake Air Temperature (IAT) sensor temperature vs. resistance values

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1. Remove the Intake Air Temperature (IAT) sensor.2. Connect a digital ohmmeter to the two terminals of the sensor.3. Using a calibrated thermometer, compare the resistance of the

sensor to the temperature of the ambient air. Refer to the temperature vs. resistance illustration.

4. Repeat the test at two other temperature points, heating or cooling the air as necessary with a hair dryer or other suitable tool.

5. If the sensor does not meet specification, it must be replaced.

Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) sensor wiring diagram

Click to Enlarge PATH:  Engine Performance & Emission Controls > Components &

Systems > Manifold Absolute Pressure Sensor > Testing Testing

Animations and Tech Tips

Click to view: Testing a MAP sensor

1. Backprobe with a high impedance voltmeter at MAP sensor terminals A and C.

2. With the key ON and engine off, the voltmeter reading should be approximately 5.0 volts.

3. If the voltage is not as specified, either the wiring to the MAP sensor or the ECM may be faulty. Correct any wiring or ECM faults before continuing test.

4. Backprobe with a high impotence voltmeter at MAP sensor terminals B and A.

5. Verify that the sensor voltage is approximately 0.5 volts with the engine not running.

6. Start the vehicle.7. Verify that the sensor voltage is greater than 1.5 volts at idle.8. Verify that the sensor voltage increases to approximately 4.5.

volts at Wide Open Throttle (WOT).9. If the sensor voltage is as specified, the sensor is functioning

properly.10. If the sensor voltage is not as specified, check the sensor and the

sensor vacuum source for a leak or a restriction. If no leaks or restrictions are found, the sensor may be defective and should be replaced.

Manifold Absolute Pressure (MAP) Sensor wiring diagram

Click to Enlarge

1. Backprobe with a high impedance voltmeter at MAP sensor terminals A and C.

2. With the key ON and engine off, the voltmeter reading should be approximately 5.0 volts.

3. If the voltage is not as specified, either the wiring to the MAP sensor or the ECM may be faulty. Correct any wiring or ECM faults before continuing test.

4. Backprobe with the high impotence voltmeter at MAP sensor terminals B and A.

5. Verify that the sensor voltage is approximately 0.5 volts with the engine not running (at sea level).

6. Record MAP sensor voltage with the key ON and engine off.7. Start the vehicle.8. Verify that the sensor voltage is greater than 1.5 volts (above the

recorded reading) at idle.9. Verify that the sensor voltage increases to approximately 4.5.

volts (above the recorded reading) at Wide Open Throttle (WOT).10. If the sensor voltage is as specified, the sensor is functioning

properly.11. If the sensor voltage is not as specified, check the sensor and the

sensor vacuum source for a leak or a restriction. If no leaks or restrictions are found, the sensor may be defective and should be replaced.

Location of the MAP sensor-TBI system shown

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Probe the terminals of the MAP sensor to check for proper reference voltage

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Manifold Absolute Pressure (MAP) sensor wiring diagram

Click to Enlarge PATH:  Engine Performance & Emission Controls > Components &

Systems > Mass Air Flow Sensor > Testing Testing

Animations and Tech Tips

Click to view: A dirty airflow sensor

1. Backprobe with a high impedance voltmeter between MAF sensor terminals C and B.

2. With the ignition ON engine off, verify that battery voltage is present.

3. If the voltage is not as specified, either the wiring to the MAF sensor, fuse or the ECM may be faulty. Correct any wiring or ECM faults before continuing test.

4. Disconnect the voltmeter and backprobe with a frequency meter between MAF sensor terminals A and B.

5. Start the engine and wait until it reaches normal idle speed and verify that the MAF sensor output is approximately 2000 Hz.

6. Slowly raise engine speed up to maximum recommended rpm and verify that the MAF sensor output rises smoothly to approximately 8000 Hz.

7. If MAF sensor output is not as specified the sensor may be faulty.

Mass Air Flow (MAF) sensor wiring diagram

Click to Enlarge PATH:  Engine Performance & Emission Controls > Components &

Systems > Oxygen Sensor > Testing > Single Wire Sensor Single Wire Sensor

Inspect the oxygen sensor tip for abnormal deposits

Jumper wires that will make sensor testing easier and

safer (for the sensor) are available from your local auto parts store

On older model vehicles, the oxygen sensor is usually located in the exhaust manifold

Click to Enlarge

1. Perform a visual inspection on the sensor as follows:1. Remove the sensor from the exhaust.2. If the sensor tip has a black/sooty deposit, this may indicate a rich

fuel mixture.3. If the sensor tip has a white gritty deposit, this may indicate an

internal anti-freeze leak.4. If the sensor tip has a brown deposit, this could indicate oil

consumption.All these contaminates can destroy the sensor, if the problem is not repaired the new sensor will also be damaged.

2. Reinstall the sensor.3. Start the engine and bring it to normal operating temperature, then

run the engine above 1200 rpm for two minutes.4. Backprobe with a high impedance averaging voltmeter (set to the

DC voltage scale) between the oxygen sensor (02S) and battery ground.

5. Verify that the 02S voltage fluctuates rapidly between 0.40-0.60 volts.

6. If the 02S voltage is stabilized at the middle of the specified range (approximately 0.45-0.55 volts) or if the 02S voltage fluctuates very slowly between the specified range (02S signal crosses 0.5 volts less than 5 times in ten seconds), the 02S may be faulty.

7. If the 02S voltage stabilizes at either end of the specified range, the ECM is probably not able to compensate for a mechanical problem such as a vacuum leak or a faulty pressure regulator. These types of mechanical problems will cause the 02S to sense a constant lean or constant rich mixture. The mechanical problem will first have to be repaired and then the 02S test repeated.

8. Pull a vacuum hose located after the throttle plate. Voltage should drop to approximately 0.12 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a lean mixture condition. Reattach the vacuum hose.

9. Richen the mixture using a propane enrichment tool. Voltage should rise to approximately 0.90 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a rich mixture condition.

10. If the 02S voltage is above or below the specified range, the 02S and/or the O2S wiring may be faulty. Check the wiring for any breaks, repair as necessary and repeat the test.

Oxygen sensor (02S) wiring diagram

Click to Enlarge PATH:  Engine Performance & Emission Controls > Components &

Systems > Positive Crankcase Ventilation System > Diagnosis & Testing Diagnosis & Testing

With the engine running, remove the PCV from the valve cover and place your thumb over the end of the valve. Check if vacuum is present at the valve. If vacuum is not present, check for plugged hoses, blockage of the manifold port at the throttle body/carburetor unit or a faulty PCV valve. Replace as necessary. With the engine not running, remove the PCV valve from the vehicle. Shake the valve and listen for the rattle of the check valve needle. If no rattle is heard the valve is defective and must be replaced.

Check the PCV valve for vacuum at idle

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