826G Landfill Compactor, 825G Soil Compactor, 824G Wheel Dozer and 980G Wheel Loader Power Train Electronic Control System Caterpillar

Illustration 1	g00772141
Schematic for the Engine Speed Sensor

This diagnostic code is recorded when the power train electronic control module (ECM) reads the signal from the engine speed sensor as being too low. The engine speed sensor is a frequency sensor. The engine speed signal wire (wire 450-YL) connects to contact 23 of control connector "J2".

Note: Ensure that the diagnostic code is active and that the diagnostic code indicator is active.

Test Step 1. Check for a Shorted Sensor.

1. Turn the disconnect switch to the OFF position.

2. Disconnect the harness from the engine speed sensor.

3. At the sensor, measure the resistance between each connector contact and the case of the sensor.

Expected Result:

The resistance of either measurement is greater than 10000 ohms.

Results:

• YES - Resistance of either measurement is greater than 10000 ohms. Proceed to test step 2.

• NO - Resistance of either measurement is less than 10000 ohms. The sensor has failed.

  Repair: Replace the sensor. Adjust the speed sensor properly, when you are installing the speed sensor. For procedures to adjust the speed sensor, refer toTesting and Adjusting, "Speed Sensor - Adjust".

  Stop.

Test Step 2. Check the Resistance at the Sensor.

1. The disconnect switch remains in the OFF position and the speed sensor remains disconnected from the harness.

2. At the sensor, measure the resistance between the two contacts of the connector.

Expected Result:

The resistance should be between 100 and 500 ohms.

Results:

• YES - Resistance is between 100 and 500 ohms. Proceed to test step 3.

• NO - Resistance is not between 100 and 500 ohms. The sensor has failed.

  Repair: Replace the sensor. Adjust the speed sensor properly, when you are installing the speed sensor. For procedures to adjust the speed sensor, refer to Testing and Adjusting, "Speed Sensor - Adjust".

  Stop.

Test Step 3. Check for a Shorted Harness.

1. The disconnect switch remains in the OFF position and the speed sensor remains disconnected from the harness.

2. Disconnect the harness from the power train ECM.

3. At the harness connector for the power train ECM, measure the resistance between contact "J2-23" (wire 450-YL) and all other connector contacts.

Expected Result:

The resistance is greater than 5000 ohms.

Results:

• YES - Resistance is greater than 5000 ohms. Proceed to test step 4.

• NO - Resistance is less than 5000 ohms.

  Repair: Wire 450-YL is shorted between the speed sensor and the power train ECM. Repair the harness or replace the harness.

  Stop.

Test Step 4. Check the Ground Circuit.

1. The disconnect switch remains in the OFF position and the speed sensor remains disconnected from the harness.

2. At the harness connector for the speed sensor, measure the resistance between contact "J1-2" (wire 202-BK) and frame ground.

Expected Result:

The resistance is less than 2 ohms.

Results:

• YES - Resistance is 2 ohms or less. Proceed to test step 5.

• NO - Resistance is greater than 2 ohms.

  Repair: Wire 202-BK has excessive resistance between the speed sensor and the frame ground. Repair the harness or replace the harness.

  Stop.

Test Step 5. Check the Signal Circuit.

1. The disconnect switch remains in the OFF position and the speed sensor remains disconnected from the harness.

2. At the harness connector for the speed sensor, place a jumper from contact 1 (wire 450-YL) to contact 2 (wire 202-BK).

3. At the harness connector for the ECM, measure the resistance between contact "J2-23" (wire 450-YL) and the frame ground.

Expected Result:

The resistance is less than 5000 ohms.

Results:

• YES - The resistance is less than 5000 ohms. Proceed to test step 6.

• NO - The resistance is greater than 5000 ohms.

  Repair: Wire 450-YL is open within the harness between the speed sensor and the power train ECM. Repair the harness or replace the harness.

  Stop.

Test Step 6. Recheck the Diagnostic Code.

1. Reconnect all harness connectors.

2. Turn the disconnect switch and the key start switch to the ON position.

3. Start the engine and run the engine at low idle.

4. Ensure that the diagnostic code is active.

5. Observe the ON/OFF status of the diagnostic code indicator.

Expected Result:

The diagnostic code indicator is not active.

Results:

• YES - The diagnostic code indicator is not active. A harness connection had failed.

  Repair: An intermittent connection exists in the speed sensor circuit of the harness. Watch for a recurrence of this diagnostic code.

  Stop.

• NO - The diagnostic code indicator is ON. Proceed to test step 7.

Test Step 7. Check the Speed Sensor Adjustment.

1. Check the speed sensor adjustment. For procedures to adjust the speed sensor, refer to Testing and Adjusting, "Speed Sensor - Adjust".

2. Ensure that the diagnostic code is active.

3. Observe the ON/OFF status of the diagnostic code indicator.

Expected Result:

The diagnostic code indicator is not active.

Results:

• YES - The diagnostic code indicator is not active.

  Repair: Adjusting the speed sensor has eliminated the diagnostic code.

  Stop.

• NO - The diagnostic code indicator is active. Proceed to test step 8.

Test Step 8. Replace the Speed Sensor.

1. Replace the speed sensor.

2. Ensure that the diagnostic code is inactive.

Expected Result:

The diagnostic code is inactive.

Results:

• YES - The diagnostic code is inactive.

  Repair: Replacing the speed sensor has eliminated the diagnostic code.

  Stop.

• NO - The diagnostic code is active.

  Repair: It is unlikely that the power train ECM has failed. Perform test steps 1 through 6 again. If the diagnostic code remains active, replace the power train ECM. For procedures to replace the power train ECM, refer to Testing and Adjusting, "Electronic Control Module (Power Train) - Replace".

  Stop.