725, 730, 735, 740 and 740 EJECTOR Articulated Trucks Power Train Electronic Control System Caterpillar

Illustration 1	g00799948
Schematic of the sensor power supply

This diagnostic code is recorded when the ECM reads the voltage of the sensor supply circuit (709-OR) and the voltage is below normal.

Test Step 1. CHECK THE VOLTAGE AT THE ECM.

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

2. Check the voltage at the connector of the ECM from contact 11 (sensor supply) to contact 12 (ground). Use the 7X-1710 Cable probes to measure the voltage. Do NOT disconnect the machine harness from the ECM.

Expected Result:

The voltage is 8.0 ± 0.5 DCV.

Results:

• OK - The voltage is 8.0 ± 0.5 DCV. The sensor supply voltage is correct. Verify that the diagnostic code is present. If the diagnostic code is still present the ECM has failed.

  Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. Also, recheck if the diagnostic code is active. If the cause of the diagnostic code is not found, replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  Stop.

• NOT OK - Voltage is NOT 8.0 ± 0.5 DCV. The voltage is less than 8.0 ± 0.5 DCV. The sensor supply voltage is NOT correct. Proceed to test step 2.

Test Step 2. CHECK FOR A SHORT TO GROUND.

1. Turn the key start switch and the disconnect switch to the OFF position.

2. Disconnect the machine harness from the ECM.

3. At the harness connector for the ECM, measure the resistance between frame ground and contact 11 of the sensor supply circuit.

Expected Result:

The resistance is greater than 5000 ohms.

Results:

• OK - The resistance is greater than 5000 ohms. The harness circuit resistance is correct. The ECM has failed.

  Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. Also, recheck if the diagnostic code is active. If the cause of the diagnostic code is not found, replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  Stop.

• NOT OK - The resistance is less than 5000 ohms. The machine harness or a sensor has failed. Proceed to test step 3.

Test Step 3. DISCONNECT THE SENSORS.

1. The key start switch and the disconnect switch remain in the OFF position.

2. One at a time, disconnect any sensor that uses the sensor supply voltage from the machine harness.

3. After disconnecting the sensor (s), check the resistance from frame ground to contact 11 (sensor supply) of the machine harness connector for the ECM.

Expected Result:

The resistance is greater than 5000 ohms.

Results:

• OK - The resistance is greater than 5000 ohms. The harness circuit resistance is correct. The sensor that was just disconnected has failed.

  Repair: Replace the sensor.

  Stop.

• NOT OK - The resistance is less than 5000 ohms. If the resistance is less than 5000 ohms after all the sensors have been disconnected from the machine harness. The machine harness is shorted to ground.

  Repair: Repair the machine harness or replace the machine harness.

  Stop.