GUARD AS 4939064 - Caterpillar

Table 1
Machine ECM (MID 39)
DTC Code Description System Response
168-3 Electrical System Voltage : Voltage Below Normal The ECM activates this diagnostic code when the system voltage is above 32.0 VDC
168-4 Electrical System Voltage : Voltage Below Normal The ECM activates this diagnostic code when the system voltage is below 18.0 VDC 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.Possible Causes for an FMI 3 diagnostic code are:
A charging system component has failed.
The harness wiring has failed.
The Machine ECM has failed. A failure of the ECM is unlikely.The FMI 3 error code will be logged when the system voltage is greater than 32.0 VDC. System electronics may be damaged if the voltage remains high for an extended time.Possible Causes for an FMI 4 diagnostic code are:
A charging system component has failed.
The harness wiring has failed.
The Machine ECM has failed. A failure of the ECM is unlikely.The FMI 4 error code will be logged when the system voltage is less than 18.0 VDC.
Illustration 1 g06145558
Electrical Schematic of the Machine ECM Electrical Power Supply
Note: The diagram above is a simplified schematic of the System Voltage connections. The schematic is electrically correct. However, not all the possible harness connectors are shown. Refer to the latest revision of Electrical Schematic, UENR0392 for the complete schematic.
Table 2
Troubleshooting Test Steps Values Results
Begin Process For DTC 168-3 Troubleshooting HERE
1. Check that Diagnostic Code is Active
A. Turn key start switch and disconnect switch ON.
B. Observe the status of the diagnostic code.
Diagnostic code remains active. OK - The diagnostic code remains active.
Proceed to Test Step 3.
NOT OK - The diagnostic code is no longer active.
Proceed to Test Step 2.
2. Check the Charging System
A. Start the engine.
B. Observe the status of the diagnostic code.
Diagnostic code is active. OK - Diagnostic code is active
Repair: The charging system is charging at an excessive voltage. Check the charging system.
See Special Instruction, SEHS0354, "Charging System Troubleshooting".
Proceed to Test Step 3.
NOT OK - Diagnostic code is not active.
Repair: There is no problem at this time. Watch for a recurrence.
STOP
3. Check The Battery Voltage
A. The engine is stopped. At the battery, measure the voltage.
The voltage is less than 32.0 VDC OK - The voltage is less than 32.0 VDC.
Repair: Exit this procedure and perform the diagnostic code procedure again. If the problem persists, the ECM may have failed. Prior to replacing to the ECM, contact the local dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. See Troubleshooting, "Electronic Control Module (ECM) - Replace"
STOP
NOT OK - The voltage is not less than 32.0 VDC.
Repair: The charging system is charging at an excessive voltage. Check the charging system. See Special Instruction, SEHS0354, "Charging