STEP AS 3747990 - Caterpillar

Table 1
Diagnostic Trouble Codes for the Electrical Power Supply
J1939 Code Code Description Comments
168-3 Electrical System Voltage : Voltage Above Normal The ECM detects voltage that is above the acceptable value.
168-4 Electrical System Voltage : Voltage Below Normal The ECM detects voltage that is below the acceptable value. The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with the electronic service tool.
Illustration 1 g03831209
Schematic diagram for the engine electrical power supply circuit
Not all connectors are shown. Refer to the appropriate electrical schematic
Complete the procedure in the order in which the steps are listed.
Table 2
Troubleshooting Test Steps Value Results
1. Determine the Diagnostic Code
A. Establish communication between the electronic service tool and the ECM . Refer to Troubleshooting, "Electronic Service Tools", if necessary.
B. Start the engine. Run the engine until the engine is at normal operating temperature.
C. Observe the "Active Diagnostic" screen on the electronic service tool. Wait at least 30 seconds so that any codes may become active.
Diagnostic code
Result: One of the diagnostic codes listed in Table 1 is active.
Proceed to Test Step 2.
Result: The electronic service tool will not communicate with the ECM.
Repair: Refer to Troubleshooting, "Electronic Service Tool Does Not Communicate".
2. Check the Charging Circuit
A. Check the charging circuit. Refer to Systems Operation, Testing and Adjusting, "Charging System - Test".
Charging circuit
Result: The charging system is OK.
Proceed to Test Step 3.
Result: The charging system is not OK.
Repair: There is a fault in the charging system. Make the necessary repairs.
Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.
3. Load Test the Batteries
A. Use a suitable battery load tester to test the batteries. Refer to Systems Operation, Testing and Adjusting, "Battery - Test" for the correct procedure.
Load test
Result: The batteries pass the load test.
Proceed to Test Step 4.
Result: The batteries do not pass the load test.
Repair: Recharge or replace the faulty batteries.
Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.
4. Inspect Electrical Connectors and Wiring
A. Ensure that the battery disconnect switch is in the CLOSED position.
B. Thoroughly inspect all connectors associated with the electrical power supplies.
C. Check all fuses.
D. Perform a 45 N (10 lb) pull test on each of the wires in the connectors associated with the electrical power supplies.
E. Check all of the wiring associated with the electrical power supplies for abrasions and pinch points.
F. If a fault is suspected with the main power relay, refer to Troubleshooting, "Relay - Test (Main Power Relay)".
Damaged wire or connector. Blown fuse.
Result: A damaged wire or damaged connector was found. A blown fuse was found.
Repair: Repair the damaged wire or the damaged connector. Replace all blown fuses.
Use the electronic service tool to clear all logged diagnostic codes. Verify that the repair eliminates the fault.
Result: A damaged wire or damaged connector was not found. The fuses are OK.
Contact the Dealer Solutions Network (DSN).