COUPLING 5M5872 - Caterpillar

Illustration 1 g02700461
Schematic of the System Voltage
This diagnostic code is recorded when the control reads the electrical system voltage (at contact 1) as being below normal range (less than 24 VDC for two seconds).The possible causes of this diagnostic code are listed below:
A charging system component has failed.
The wire harness has failed.
The ECM has failed (unlikely).System Response:The outputs of the control may operate incorrectly.Note: Make sure that the 10 Amp fuse is not open.Test Step 1. CHECK FOR AN ACTIVE DIAGNOSTIC CODE
Start the engine.
Run the engine at high idle.
View the status of the diagnostic code. Expected Result:The diagnostic code is NOT active.Results:
YES - The diagnostic code is NOT active. The problem does not exist at this time. Watch for a recurrence.STOP
NO - The diagnostic code is active. Proceed to Test Step 2.Test Step 2. CHECK THE BATTERY VOLTAGE
Measure the system voltage at the battery posts. Expected Result:The voltage is greater than 24 VDC.Results:
YES - The voltage is greater than 24 VDC. Proceed to Test Step 3.
NO - The voltage is less than 24 VDC. Repair: The charging system is not correct. Check the charging system. See Special Instruction, REHS0354, "Charging System Troubleshooting". STOPTest Step 3. CHECK THE SYSTEM VOLTAGE AT THE ECM
Turn the disconnect switch and the key start switch to the OFF position.
Disconnect the machine harness connector from the control.
Turn the disconnect switch and the key start switch to the ON position.
Run the engine at high idle.
At the machine harness connector for the ECM, measure the voltage between contact 1 and contact 2. Expected Result:The voltage is greater than 24 VDC.Results:
YES - The voltage is greater 24 VDC. A voltage greater than 24 VDC should not cause the diagnostic code. Repair: Inspect the connector. Connect the machine harness to the ECM. Check all connectors in the wire harness. If the CID 0168 FMI 04 remains active, replace the control. See Testing and Adjusting, "Module - Replace".STOP
NO - The voltage is less than 24 VDC. The machine harness has failed. Repair: Check the +battery circuit and the ground circuit in the machine harness. Repair or replace the machine harness. STOP