BOLT 0953388 - Caterpillar

If the backup alarm is always ON, the harness circuit is shorted to the +battery circuit or the ECM has failed. Test Step 1. CHECK THE CIRCUIT FOR THE BACKUP ALARM FOR A SHORT TO THE +BATTERY CIRCUIT.
Turn the key start switch and the disconnect switch to the OFF position.
Disconnect the machine harness from the backup alarm.
Disconnect the machine harness connector J1 and connector J2 from the ECM.
At machine harness connector J2, measure the resistance from the J2-37 (backup alarm signal) to all possible sources of +battery. The possible sources of positive voltage are contacts J1-1, J1-4, J1-6, J1-8, J1-10, J1-11, J1-12, J1-17, J1-18, J1-40, J2-1, J2-2, J2-7, J2-8, J2-13 andJ2-19. Expected Result: Each resistance should be greater than 5000 ohms. Results:
OK - The machine harness is correct. Proceed to test step 2.
NOT OK - There is a short in the machine harness. The harness has failed.Repair: The short is between wire 321-BR(Brown) (backup alarm signal) and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness.STOPTest Step 2. CHECK IF THE PROBLEM IS STILL ACTIVE.
Inspect the contacts of the harness connectors and clean the contacts of the harness connectors.
Reconnect all harness connectors.
Start the engine. Expected Result: The backup alarm is always ON regardless of the position of the transmission lever. Results:
YES - The problem has not been corrected. The ECM has failed.Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. Replace the ECM if the cause is not found. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace". STOP
NO - The problem is NOT present. Repair: The problem does not exist at this time. The initial problem was probably caused by a poor electrical connection and/or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.STOP