CONTROL GP-ENGINE ELECTRONIC 4380979 - Caterpillar

Probable Causes
The backup alarm has failed.
The harness circuit is shorted to ground. (alarm is always ON)
The harness circuit is open. (alarm does not sound)
The ECM has failed.Note: Ensure that there are no active diagnostic codes for the direction switch.Recommended Actions
The Backup Alarm Has Failed
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.Result:YES: The backup alarm sounds when power is applied. Proceed to "The Harness Circuit Is Shorted To Ground. (Alarm Is Always On)".NO: The backup alarm does NOT sound. The backup alarm has failed.Repair: Replace the backup alarm.STOP.The Harness Circuit Is Shorted To Ground. (Alarm Is Always On)
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 J2-6 (wire 321-BR(Brown)) and all possible sources of ground. Expected Result:Each resistance should be greater than 5000 ohms.Result:YES: The resistance is greater than 5 Ohms (no continuity). The resistance of the harness circuit is correct. Proceed to "The Harness Circuit Is Open. (Alarm Does Not Sound)".NO:The resistance is less than 5 Ohms (continuity). The harness has failed. Wire (321-BR(Brown)) is shorted to ground in the harness.Repair: Repair the harness or replace the harness.STOP.The Harness Circuit Is Open. (Alarm Does Not Sound)
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 J2-6 (wire 321-BR(Brown)) to ground.
At the harness for the backup alarm, measure the resistance from wire 321-BR(Brown) to ground. Expected Result:There should be continuity.Result:YES: The resistance is less than 5 Ohms (continuity). The harness circuit resistance is correct. It is unlikely that the ECM has failed. Perform these Steps again.If the cause is not found, replace the ECM. Refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace" in this manual.NO: The resistance is greater than 5000 Ohms (no continuity). The harness circuit has failed. Wire (321-BR(Brown)) is open in the harness between the ECM and the backup alarm relay.Repair: Repair the harness or replace the harness.STOP.