966G Wheel Loader and 972G Wheel Loader Power Train Caterpillar

Illustration 1	g00450651
Schematic of the Backup Alarm

The power train electronic control module (ECM) applies power to the backup alarm whenever the power train ECM receives a signal from the reverse direction switch.

The Backup Alarm is Always ON

If the backup alarm is always ON, the harness circuit is shorted to the +battery or the power train ECM is faulty.

1. Check for a shorted harness.

   Turn the disconnect switch to the OFF position. Disconnect the machine harness connector from the power train ECM. Disconnect the backup alarm from the machine harness. At the machine harness connector for the power train ECM, measure the resistance between connector contact J2-37 (wire 321-BR) and all other possible sources of +battery.

   • A resistance measurement is less than 5000 Ohms (continuity). The machine harness is faulty. The corresponding wire is shorted to wire 321-BR within the machine harness. Repair the machine harness or replace the machine harness.

   • All the resistance measurements are greater than 5000 Ohms (no continuity). The resistance to the harness circuit is correct. It is unlikely that the power train ECM is faulty. Perform Step 1 again. If the cause is not found, replace the power train ECM. Refer to Testing And Adjusting, "Electronic Control Module (Power Train) - Replace" for more information on replacing the power train ECM.

The Backup Alarm is Always OFF

If the backup alarm is always OFF one of the following causes are responsible:

• A fault in the backup alarm

• An open in the harness circuit

• A short to ground in the harness circuit

• A fault in the power train electronic control module (ECM)

1. Check the backup alarm.

   Disconnect the backup alarm from the machine harness. Use jumpers to connect the respective terminals of the backup alarm to +battery and ground. Apply power to the backup alarm and determine if the backup alarm sounds.

   The backup alarm does NOT sound. The backup alarm is faulty. Replace the backup alarm.

   The backup alarm sounds. The backup alarm is operating correctly. Proceed to Step 2.

2. Check for a shorted harness.

   Turn the disconnect switch to the OFF position. The backup alarm remains disconnected. Disconnect the power train ECM from the machine harness. At the machine harness connector for the power train ECM, measure the resistance between connector contact J2-37 (wire 321-BR) and connector contact J1-7 (ground) or connector contact J2-3 (ground).

   • The resistance is less than 5000 Ohms (continuity). The machine harness is faulty. Wire 321-BR is shorted to ground in the machine harness. Repair the machine harness or replace the machine harness.

   • The resistance is greater than 5000 Ohms (no continuity). The resistance of the harness circuit is correct. Proceed to Step 3.

3. Check for an open in the harness.

   The disconnect switch remains OFF. The backup alarm and the power train ECM remain disconnected from the machine harness. At the machine harness connector for the power train ECM, place a jumper from connector contact J2-37 (wire 321-BR) to connector contact J2-3 (wire 975-WH). At the machine harness for the backup alarm, measure the resistance between wire 975-WH and wire 321-BR.

   • The resistance is greater than 5000 Ohms (no continuity). The harness circuit is faulty. Wire 975-WH or wire 321-BR is open in the machine harness between the power train ECM and the backup alarm. Repair the machine harness or replace the machine harness.

   • The resistance is less than 5000 Ohms (continuity). The harness circuit resistance is correct. It is unlikely that the power train ECM is faulty. Perform the steps that follow again: Step 1, Step 2 and Step 3. If the cause is not found, replace the power train ECM. Refer to Testing And Adjusting, "Electronic Control Module (Power Train) - Replace" for more information on replacing the power train ECM.