Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the Electronic Control Module (ECM). Also use this procedure if any one of the diagnostic codes in Table 1 is active or easily repeated.
| Diagnostic Trouble Codes | ||
|---|---|---|
| J1939 Code and Description | Conditions that Generate the Code | System Response |
| 158-2 Keyswitch Battery Potential : Erratic, Intermittent, or Incorrect | The ECM detects an erratic signal from the keyswitch. The keyswitch is cycled at least three times in the last second. | The code is logged. |
| 168-2 Battery Potential / Power Input 1 : 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 seven seconds. | The code is logged. |
| 168-3 Battery Potential / Power Input 1 : Voltage Above Normal | The ECM detects voltage that is above the acceptable value. | The code is logged. |
| 168-4 Battery Potential / Power Input 1 : Voltage Below Normal | The ECM detects voltage that is below the acceptable value. | The code is logged. |
The engine ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).
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| Illustration 1 | g02060084 |
|
Schematic for the electrical power supply circuit | |
Test Step 1. Check for Active Diagnostic Codes
- Establish communication between Cat ET and the ECM . Refer to Troubleshooting, "Electronic Service Tools", if necessary.
- Start the engine. Run the engine until the engine is at normal operating temperature.
- Observe the "Active Diagnostic" screen on Cat ET. Wait at least 30 seconds so that any codes may become active.
Look for these codes:
- 168-2
- 168-3
- 168-4
Results:
- Active 168-2 or 158-2 - Proceed to Test Step 2.
- Active 168-3 - Proceed to Test Step 3.
- Active 168-4 - Proceed to Test Step 4.
Test Step 2. Inspect the Electrical Connectors and the Wiring for the Charging Circuit
- Turn the keyswitch to the OFF position.
- Check the harness connections at the battery and at the alternator.
- Check the harness between the battery and the alternator.
Results:
- OK - The harness and connectors appear to be OK.
Repair: There is a problem with the charging system. Refer to Special Instruction, REHS0354, "Charging System Troubleshooting".
STOP
- Not OK - The connectors and/or wiring are not OK.
Repair: 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.
STOP
Test Step 3. Check the Charging Circuit
- There is a problem with the charging circuit.
Results:
- Not OK - The battery voltage is high.
Repair: There is a problem with the charging system. Refer to Special Instruction, REHS0354, "Charging System Troubleshooting".
STOP
Test Step 4. Check the Battery
- Turn the keyswitch to the ON position. Do not start the engine.
- Check the brightness of the lights.
- Turn the keyswitch to the ON position. Start the engine.
- Check the brightness of the lights.
Expected Result:
The battery appears to be OK.
Results:
- OK - The lights are dim when the engine is not running. The lights are brighter when the engine is running. There is a problem with the battery. Proceed to Test Step 5.
- Not OK - The lights are dim when the engine is not running. The lights are still dim when the engine is running.
Repair: There is a problem with the charging system. Refer to Special Instruction, REHS0354, "Charging System Troubleshooting".
STOP
Test Step 5. Check the Battery Charge
- Measure the no-load battery voltage at the battery posts.
- 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 and 12 Volt Lead Acid Batteries" and Special Instruction, SEHS7633, "Battery Test Procedure".
Results:
- OK - The batteries pass the load test. The voltage is between 11.0 V and 13.5 V for a 12 V system. The voltage is between 22.0 V and 27.0 V for a 24 V system.
Repair: Check the wiring between the batteries and the ECM.
Check the connectors between the batteries and the ECM for moisture and/or corrosion.
Repair the wiring and/or the connectors.
Verify that the repair eliminates the problem.
STOP
- Not OK - The battery voltage is low or the battery did not pass the load test.
Repair: Recharge or replace the faulty batteries. Verify that the repair eliminates the problem.
STOP