416E, 420E and 430E Backhoe Loaders Backup Alarm Always Off Caterpillar

System Operation Description:

Illustration 1	g01662373
Schematic for the Backup Alarm

The ECM applies power to the backup alarm whenever the ECM receives a signal from the reverse direction switch.

The possible causes for the backup alarm are listed below:

• The backup alarm has failed.

• The harness circuit is open.

• The harness circuit is shorted to ground.

• The ECM has failed.

Note: Ensure that there are no active diagnostic codes for the direction switch.

Test Step 1. CHECK THE BACKUP ALARM

1. Disconnect the backup alarm from the harness.

2. Use jumpers to connect the respective terminals of the backup alarm to a + battery and ground.

Expected Result:

The backup alarm sounds when power is applied.

Results:

• YES - The backup sounds when power is applied. Proceed to Test Step 2.

• NO - The backup alarm does NOT sound. The backup alarm has failed.

  Repair: Replace the backup alarm.

  STOP

Test Step 2. CHECK FOR A SHORTED HARNESS

The backup alarm remains disconnected.

1. Turn the disconnect switch to the OFF position.

2. Disconnect the ECM from the harness.

3. At the harness connector for the ECM, measure the resistance between contact J2-13 (wire 331-OR) and all possible sources of ground.

Expected Result:

Each resistance should be greater than 5000 ohms.

Results:

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

• NO - The resistance is less than 5000 Ohms (continuity). The harness has failed. Wire 331-OR is shorted to ground in the harness.

  Repair: Repair the harness or replace the harness.

  STOP

Test Step 3. CHECK FOR AN OPEN IN THE HARNESS

The backup alarm and the ECM remain disconnected from the harness.

1. The disconnect switch remains in the OFF position.

2. At the harness connector for the ECM, place a jumper from contact J2-13 (wire 331-BR) to ground.

3. At the harness for the backup alarm, measure the resistance between wire 331-OR to ground.

Expected Result:

There should be continuity.

Results:

• YES - The resistance is less than 5000 Ohms (continuity). The harness circuit resistance is correct. It is unlikely that the ECM has failed. Perform these Steps again.

  Repair: If the cause is not found, replace the ECM. See Troubleshooting, "Electronic Control Module (ECM) - Replace".

  STOP

• NO - The resistance is greater than 5000 Ohms (no continuity). The harness circuit has failed. Wire (331-OR) is open in the harness between the ECM and the backup alarm relay.

  Repair: Repair the harness or replace the harness.

  STOP