Use this procedure to troubleshoot any suspect problems with the electrical power supply.
This procedure covers the following diagnostic codes:
- 168-00 System Voltage High
- 168-01 System Voltage Low
- 168-02 System Voltage intermittent/erratic
This procedure tests whether proper voltage is being supplied to the Electronic Control Module (ECM).
Unswitched battery voltage is supplied through the customer connector to the ECM at P1-48, P1-52, and P1-53. The negative battery is supplied to the ECM at P1-61, P1-63, and P1-65. The ECM receives the input from the keyswitch at P1-70 when the keyswitch is in the ON position or in the START position. When the ECM detects battery voltage at this input, the ECM will power up. When battery voltage is removed from this input, the ECM will power down.
The cause of an intermittent power supply to the ECM can occur on either the positive side or the negative side of the battery circuit. Both sides of the circuit are routed directly from the battery to the ECM. The three connections for the unswitched +Battery must be routed through a dedicated protective device (circuit breaker).
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 | g01181797 |
Schematic diagram for the electrical power supply | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Turn the keyswitch to the OFF position.
- Thoroughly inspect the J1/P1 ECM connector, the battery connections, and the connections to the keyswitch. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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| Illustration 2 | g01183529 |
Location of the P1 ECM connector (typical left side engine view) | |
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the electrical power supply.
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| Illustration 3 | g01112632 |
P1 terminal locations for the electrical power supply (P1-48) +Battery (P1-52) +Battery (P1-53) +Battery (P1-61) −Battery (P1-63) −Battery (P1-65) −Battery (P1-70) Keyswitch | |
- Check the allen head screw for each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
- Check the harness and wiring for abrasions and for pinch points from the battery to the ECM. Also, check the harness and wiring for abrasions and for pinch points from the keyswitch to the ECM.
Expected Result:
All connectors, pins, and sockets are completely inserted and coupled. The harness and wiring are free of corrosion, of abrasion, and of pinch points.
Results:
- OK - The harness and wiring appear to be OK. Proceed to Test Step 2.
- Not OK - There is a problem in the connectors and/or wiring.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled. Verify that the repair eliminates the problem.
STOP
Test Step 2. Check the Battery Voltage at the ECM
- Disconnect the J1/P1 ECM connector.
- Measure the voltage between P1-52 (+Battery) and P1-63 (−Battery).
- Measure the voltage between P1-48 (+Battery) and P1-61 (−Battery).
- Measure the voltage between P1-53 (+Battery) and P1-65 (−Battery).
- Turn the keyswitch to the ON position.
- Measure the voltage between P1-70 (Keyswitch) and P1-63 (−Battery).
Expected Result:
The measured voltage is between 11.0 VDC and 13.5 VDC for a 12 volt system and between 22.0 VDC and 27.0 VDC for a 24 volt system with no suspected intermittent problems at this time.
Results:
- OK - The ECM is receiving the correct voltage.
Repair: If an intermittent condition is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect".
STOP
- Not OK - Battery voltage is out of range - Proceed to Test Step 3.
- Not OK - Keyswitch voltage out of range -
Repair: Trace the wiring for the keyswitch from the ECM through the keyswitch circuit to the batteries. Find the problem and repair the problem. Check the circuit protection for the circuit and for the wiring.Verify that the repairs eliminate the problem.
STOP
Test Step 3. Check the Condition of the Batteries
- 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".
Expected Result:
The batteries pass the load test. The measured voltage is the minimum specification for a 12V or 24V system.
Results:
- OK - The batteries are OK.
Repair: Check the wiring between the batteries and the ECM for an open circuit or a short circuit.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