HARNESS AS-MAIN CAB 3168515 - Caterpillar

Possible causes for an FMI 3 Diagnostic code are:
The return circuit is open.
The signal circuit is open or the alarm is disconnected.
The signal circuit is shorted to the +battery.
The alarm has failed.
The ECM has failed. This condition is unlikely.Possible causes for an FMI 5 Diagnostic code are:
The alarm has failed.
The signal circuit for the alarm is shorted to ground.
The ECM has failed. A failure of the ECM is unlikely.Possible causes for an FMI 6 Diagnostic code are:
The energize circuit of the backup alarm is shorted to ground.
The backup alarm has failed.
The ECM has failed. This condition is unlikely.
Illustration 1 g03592339
Schematic of the Alarm circuits
Note: The diagram above is a simplified schematic of the connections for the alarm circuits. The schematic is electrically correct. However, not all of the possible harness connectors are shown. Refer to the latest revision of the Electrical Schematic, UENR6729 for the complete schematic.Diagnostic Trouble Code Procedure
Note: Prior to beginning this procedure, inspect the harness connectors that are involved in this circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, secure, and in good condition. If a problem with a connection is found, correct the problem and verify that the diagnostic code is active before performing a troubleshooting procedure. For sensors powered via the fuse panel, check the condition of the appropriate fuse before beginning the troubleshooting procedure.
Table 2
Troubleshooting Test Steps Values Results
1. Identify The Active DTC Code Associated With The Suspect Circuit
Code present. FMI 3 diagnostic code, proceed to Test Step 2.
FMI 5 diagnostic code, proceed to Test Step 3.
FMI 6 diagnostic code, proceed to Test Step 8.
Begin Process For FMI 3 Troubleshooting HERE
2. Check The Energize Circuit Of The Alarm For A Short To The +Battery Circuit.
A. Turn the key start switch and the disconnect switch to the OFF position.
B. Disconnect the alarm with the active diagnostic code from the machine harness. Disconnect the harness from the ECM.
C. At the machine harness connector for the ECM, measure the resistance from the signal harness contact for the alarm to all contacts used in the machine harness connectors for the ECM.
Each resistance measurement is greater than 5K ohms. OK - Each resistance measurement is greater than 5K ohms. The machine harness is correct.
Proceed to Test Step 9.
NOT OK - Each resistance measurement is not greater than 5K ohms. There is a short in the machine harness. The short is between the signal wire for the alarm and the wire that measured low resistance.
Repair: Repair the machine harness or replace the machine harness.
Proceed to Test Step 9.
Begin Process For FMI 5 Troubleshooting HERE
3. Check The Alarm
A. Turn key start switch and disconnect switch ON.
B. Ensure that the diagnostic code is active.
C. Disconnect the alarm with the active diagnostic code from the machine harness.
D. At the machine harness connector for the alarm, place a jumper wire from contact 1 to contact 2.
E. Observe the status of the diagnostic code.
The diagnostic code remains active.