System Operation Description:
Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the engine Electronic Control Module (ECM). Also use this procedure if any one of the diagnostic codes in Table 1 is active or easily repeated.
Note: Some of the following codes may not be applicable for certain applications.
|Diagnostic Trouble Codes|
|J1939 Code||CDL Code||Code Description||Comments|
|168-2||168-2||Electrical System Voltage : Erratic, Intermittent, or Incorrect||The engine is running. The battery voltage falls below 6 VDC and the voltage returns above 9 VDC for three voltage readings in the last 7 seconds.|
|168-3||168-3||Electrical System Voltage : Voltage Above Normal||The ECM detects voltage that is above the acceptable value.|
|168-4||168-4||Electrical System Voltage : Voltage Below Normal||The ECM detects voltage that is below the acceptable value.|
|158-2||1834-2||Ignition Key Switch loss of signal||The ECM detects an erratic signal from the keyswitch because the keyswitch was cycled at least three times in the last second|
The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).
Illustration 2 g02361008
Terminal locations at the P1 ECM connector that are for electrical power
(P1-48) +Battery (if applicable)
(P1-52) +Battery (if applicable)
(P1-53) +Battery (if applicable)
(P1-55) +Battery (if applicable)
(P1-57) +Battery (if applicable)
(P1-61) -Battery (if applicable)
(P1-63) -Battery (if applicable)
(P1-65) -Battery (if applicable)
(P1-67) -Battery (if applicable)
(P1-69) -Battery (if applicable)
|Troubleshooting Test Steps||Values||Results|
1. Determine the Diagnostic Code
A. Establish communication between the Cat ET 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. Download the “Warranty Report” from the engine ECM before performing any troubleshooting or clearing diagnostic trouble codes. Look for these codes:
Result: A 168-2 or a 1834-2 diagnostic code is active.
Proceed to Test Step 2.
Result: A 168-3 diagnostic code is active.
Proceed to Test Step 3.
Result: A 168-4 diagnostic code is active.
Proceed to Test Step 4.
2. Inspect the Electrical Connectors and the Wiring For the Charging Circuit
A. Turn the keyswitch to the OFF position.
B. Check the harness connections at the battery and at the alternator.
C. Check the harness between the battery and the alternator.
|Connectors and wiring||
Result: OK – The harness and connectors appear to be OK.
There is a problem with the charging system. Refer to Special Instruction, REHS0354, “Charging System Troubleshooting”.
Result: Not OK – The connectors and/or wiring are not OK.
Repair the wiring and/or the connectors. Replace parts, if necessary. Ensure that all of the seals are properly in place and ensure that the connectors are coupled. Verify that the repair eliminates the problem.
3. Check the Charging Circuit
A. Check the charging circuit. Refer to Special Instruction, REHS0354, “Charging System Troubleshooting”.
Result: OK – The charging system is OK.
Proceed to Test Step 4.
Result: The charging system is not OK. There is a problem with the charging system. Refer to Special Instruction, REHS0354, “Charging System Troubleshooting”.
4. Check the Battery Charge
A. Measure the no-load battery voltage at the battery posts.
B. Load-test the batteries. Use the 4C-4911 Battery Load Tester . Refer to Special Instruction, SEHS9249, “Use of 4C-4911 Battery Load Tester for 6, 8 V and 12 V Lead Acid Batteries” and Special Instruction, SEHS7633, “Battery Test Procedure”.
Result: OK – The batteries pass the load test. The measured voltage is between 11.0 VDC and 13.5 VDC for a 12 v system. The measured voltage is between 22.0 VDC and 27.0 VDC for a 24 v system.
Verify that the “System Operating Voltage Configuration” is correctly configured in the Engine ECM configuration parameters.
Result: Not OK – The battery voltage is low or the battery did not pass the load test.
Recharge or replace the faulty batteries. Verify that the repair eliminates the problem.
Test Step 1.
Complete the procedure in the order in which the steps are listed.
- The procedure corrected the issue. – STOP
- The procedure did not correct the issue. –Repair: Contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).