PLATE AS 2321861 - Caterpillar

Illustration 1 g02645821
Schematic for the Backup AlarmThe ECM applies power to the backup alarm relay whenever the ECM receives a reverse signal from the shift lever.The possible causes for the backup alarm "always off" are listed below:
The fuse is open.
The backup alarm has failed.
The harness circuit is open.
The harness circuit is shorted to ground.
The relay has failed.
The ECM has failed.Test Step 1. CHECK THE FUSE
Measure the resistance across the terminals of fuse G5.Expected Result:The resistance is less than 1 ohm.Results:
OK - The resistance is less than 1 ohm. The fuse is correct. Proceed to Test Step 2.
NOT OK - The resistance is greater than 1 ohm. The fuse is open. Proceed to Test Step 3 prior to replacing the fuse. Test Step 2. CHECK THE BACKUP ALARM
Disconnect the backup alarm from the harness.
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 3.
NO - The backup alarm does NOT sound. The backup alarm has failed.Repair: Replace the backup alarm.STOPTest Step 3. CHECK FOR A SHORTED HARNESS
Turn the disconnect switch to the OFF position.
Disconnect the backup alarm and backup lamps from the circuit if not previously done.
At the harness connector for the backup alarm, measure the resistance between contact 1 (wire 612-GY) 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 4.
NO - The resistance is less than 5000 Ohms (continuity). The harness has failed. Wire 612-GY is shorted to ground in the harness.Repair: Repair the harness or replace the harness.STOPTest Step 4. CHECK FOR AN OPEN IN THE HARNESSThe backup alarm remains disconnected from the harness.
The disconnect switch remains in the OFF position.
At the harness connector for the backup alarm, place a jumper from contact 1 (wire 612-GY) and contact 2 (wire 200-BK).
At the harness for the backup alarm relay, measure the resistance between contact 87 (wire 612-GY) and ground.Expected Result:There should be continuity.Results:
YES - The resistance is less than 5000 Ohms (continuity). The harness circuit resistance is correct. The relay is most likely causing the problem.Repair: Replace the relay. After replacement of the relay, check the operation of the backup alarm before operating.STOP
NO - The resistance is greater than 5000 Ohms (no continuity). The harness circuit has failed. Wire (612-RD) is open in the harness between the backup alarm and the backup alarm relay.Repair: Repair the harness or replace the harness.STOP