992G Wheel Loader and 854G Wheel Dozer Power Train Caterpillar

Illustration 1	g01057821

The power train ECM applies power to the backup alarm whenever the gear selector is placed in reverse position.

One of the following conditions can cause the backup alarm to remain ON:

• The harness circuit is shorted to the + battery.

• The ECM may have failed. This is unlikely.

Test Step 1. CHECK THE BACKUP ALARM RELAY.

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

2. Turn the disconnect switch to the ON position.

3. Remove the backup alarm relay from the relay socket.

Expected Result:

The backup alarm shuts off.

Results:

• OK - The backup alarm shuts off. The backup alarm relay has failed.

  Repair: Replace the backup alarm relay. Verify that the new relay has corrected the problem.

  Stop.

• NOT OK - The backup alarm does not shut off. The backup alarm relay is not the problem. Put the backup alarm relay in the relay socket. Proceed to test step2.

Test Step 2. CHECK FOR A SHORT TO THE +BATTERY CIRCUIT.

1. Turn the disconnect switch to the OFF position.

2. The key start switch remains in the OFF position.

3. Disconnect the machine harness from the backup alarm.

4. Measure the resistance from contact J2-37 (wire 321-BR) to all sources of + battery. The possible sources of positive voltage are contacts J1-1, J1-6, J1-8, J1-11, J1-18, J1-40, J2-1, J2-7, J2-8, J2-13, and J2-19.

Expected Result:

Each resistance measurement should be greater than 5000 ohms.

Results:

• OK - Each resistance measurement is greater than 5000 ohms. The machine harness is correct. Proceed to test step 3.

• NOT OK - Each resistance measurement is not greater than 5000 ohms.

  Repair: There is a short in the machine harness. The short is between the backup alarm signal (wire 321-BR) and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness.

  Stop.

Test Step 3. CHECK IF THE ABNORMAL CONDITION REMAINS.

1. Inspect the harness connectors and clean the contacts of the harness connectors.

2. Reconnect all harness connectors.

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

4. Start the engine.

Expected Result:

The backup alarm is always ON regardless of the position of the gear lever.

Results:

• YES - The backup alarm is always ON regardless of the position of the gear lever. The ECM has failed.

  Repair: The problem has not been corrected. It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the cause of the failure is not found, replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  Stop.

• NO - The backup alarm is not always ON regardless of the position of the gear lever. The failure is NOT present. The problem does not exist at this time. The initial problem was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation. Stop.