Use this test if there are intermittent engine shutdowns or if a difficulty in starting is not accompanied by loss of electrical accessories. Engine shutdowns that are accompanied by a loss of other electrical accessories indicate a problem in the keyswitch. This does not indicate a problem in the wiring at the engine's Electronic Control Module (ECM). Verify that there are no problems with the starting system or the charging system before you use this test.
Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the engine's ECM or if any one of the diagnostic codes or the event code in Table 1 is active or easily repeated.
| Diagnostic Codes Table | ||
| Diagnostic Codes Table | Conditions which Generate this Code | System Response |
| 168-0 Electrical System Voltage high - most severe (3) | The ECM reads battery voltage that is above 16 VDC. | The code is logged. |
| 168-1 Electrical System Voltage low - most severe (3) | The ECM reads battery voltage that is below 9 VDC. | |
| 168-2 Electrical System Voltage erratic, intermittent, or incorrect | While the engine is running, the battery voltage drops below 9 VDC intermittently, or the battery voltage drops below 9 VDC three times in a seven second period. | |
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 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.
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| Illustration 1 | g01382599 |
Schematic diagram for the electrical power supply (typical wiring suggestion) | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Remove the electrical power from the ECM.
- Check for a tripped circuit breaker.
- Thoroughly inspect the J1/P1 ECM connectors. Inspect the connections for the battery and the connections to the keyswitch. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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| Illustration 2 | g01214624 |
Location of the J1/P1 ECM connectors (typical engine view) | |
- Perform a 45 N (10 lb) pull test on each of the wires that are associated with the electrical power supply.
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| Illustration 3 | g01378728 |
Terminal locations at the P1 ECM connector that are associated with 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 on each ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
- 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 coupled and/or inserted, and the harness and wiring are free of corrosion, of abrasion and of pinch points.
Results:
- OK - The connectors and wiring are OK. Proceed to Test Step 2.
- Not OK - There is a problem with the connectors 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.
STOP
Test Step 2. Check the Battery Voltage at the ECM
- Disconnect the J1/P1 ECM connector.
- Restore the electrical power to the ECM.
- Turn the keyswitch to the ON position.
- 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).
- 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 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
- Battery voltage is out of range - Proceed to Test Step 3.
- Keyswitch voltage out of range - The voltage is not correct for the keyswitch circuit at the ECM. Proceed to Test Step 4.
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 above the minimum specification for the batteries.
Results:
- OK - The batteries are OK.
Repair: Check the wiring between the batteries and the ECM for shorts.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
Test Step 4. Check the Voltages at the Battery and the Keyswitch
- Remove electrical power from the ECM.
- Remove the wire from the terminal R of the keyswitch.
- Restore electrical power to the ECM.
- Turn the keyswitch to the ON position.
- Measure the voltage between terminal B of the keyswitch and engine ground.
- Measure the voltage between terminal R of the keyswitch and engine ground.
- Remove electrical power from the engine ECM.
Expected Result:
Voltage is present on terminal B and terminal R at the keyswitch.
Results:
- OK - Voltage is present on terminal B and terminal R at the keyswitch.
Repair: Check continuity of wire J906-BR between the keyswitch and the ECM. Verify that the wire does not have a short or an open.
STOP
- Not OK - Voltage is not present on terminal B at the keyswitch.
Repair: If voltage is not present on terminal B, repair the circuit between the +Battery and the keyswitch. Check the circuit protection for the circuit. Verify that the problem is eliminated.
STOP
- Not OK - Voltage is not present on terminal R at the keyswitch.
Repair: If voltage is present on terminal B of the keyswitch but not present on terminal R, replace the keyswitch. Return all wiring to the original configuration. Verify that the problem is eliminated.
STOP