DISC 1260827 - Caterpillar

Illustration 1 g00588671
Schematic for the Backup AlarmThe 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:
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
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 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 HARNESSThe backup alarm remains disconnected.
Turn the disconnect switch to the OFF position.
Disconnect the ECM from the harness.
At the harness connector for the ECM, measure the resistance between contact J2-37 (wire 321-BR) and contact J1-2 (ground) or contact J1-5 (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 321-BR 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 HARNESSThe backup alarm and the ECM remain disconnected from the harness.
The disconnect switch remains OFF.
At the harness connector for the ECM, place a jumper from contact J2-37 (wire 321-BR) to contact J2-3 (wire 975-WH).
At the harness for the backup alarm, measure the resistance between wire 975-WH and wire 321-BR.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 Testing And Adjusting, "Electronic Control Module (ECM) - Replace". Stop.
NO - The resistance is greater than 5000 Ohms (no continuity). The harness circuit has failed. Wire 975-WH or wire 321-BR is open in the harness between the ECM and the backup alarm.Repair: Repair the harness or replace the harness. Stop.