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 with the wiring at the 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 ECM or if any one of the diagnostic codes in Table 1 is active or easily repeated.
| Diagnostic Codes Table | ||
|---|---|---|
| Code and Description | Conditions which Generate this Code | System Response |
| 168-0 Electrical System Voltage high - most severe (3) | The battery supply voltage is greater than 32 VDC for 0.5 seconds. The engine's ECM has been powered for three seconds. The engine has been running for at least 30 seconds. |
The code is logged. |
| 168-1 Electrical System Voltage low - most severe (3) | The battery supply voltage is less than 9 VDC for 0.5 seconds. The engine's ECM has been powered for three seconds. The engine is running for at least 3 seconds. |
|
| 168-2 Electrical System Voltage erratic, intermittent, or incorrect | The battery voltage falls below 6 VDC and the voltage returns above 9 VDC for three voltage readings in the last seven seconds. The engine is running. |
|
Unswitched battery voltage is supplied to the ECM at P1-48, P1-52, P1-53, P1-55, and P1-57. The negative battery is supplied to the ECM at P1-61, P1-63, P1-65 and P1-67. 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 ECM continuously receives battery voltage through the circuit breaker for the ECM.
The ECM requires the keyswitch to be in the ON position in order to maintain communications with Caterpillar Electronic Technician (ET).
 | |
| Illustration 1 | g01377847 |
Schematic for the electrical power supply circuit | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Remove electrical power from the engine ECM.
- Thoroughly inspect connectors (1) and (2). Inspect all of the connectors that are in the circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
 | |
| Illustration 2 | g01377328 |
Location of the connectors that are for the electrical power supply circuit (rear engine view) (1) J1/P1 ECM connectors (2) Customer connector | |
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
 | |
| Illustration 3 | g01377860 |
(P1-48) +Battery (P1-52) +Battery (P1-53) +Battery (P1-55) +Battery (P1-57) +Battery (P1-61) -Battery (P1-63) -Battery (P1-65) -Battery | |
- Check the allen head screw for each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
- Check the harness and the wiring for abrasion and for pinch points.
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. All connections are tight and free of corrosion.
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
- Remove electrical power from the ECM.
- Disconnect the J1/P1 ECM connector.
- Restore electrical power to the ECM.
- Turn the keyswitch to the ON position.
- Wiggle the wires in the harness while performing the following test steps.
- Measure the voltage between P1-48 (unswitched +Battery) and P1-61 (−Battery).
- Measure the voltage between P1-52 (unswitched +Battery) and P1-63 (−Battery).
- Measure the voltage between P1-53 (unswitched +Battery) and P1-65 (−Battery).
- Measure the voltage between P1-55 (unswitched +Battery) and P1-67 (−Battery).
- Measure the voltage between P1-57 (unswitched +Battery) and P1-67 (−Battery).
- Measure the voltage between P1-70 (keyswitch) and P1-63 (−Battery).
Expected Result:
The measured voltage is between 22 VDC and 27 VDC.
Results:
- OK - The ECM is receiving the correct voltage.
Repair: There may be an intermittent electrical problem in a harness or in a connector. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect".
STOP
- Battery voltage out of range - The voltage is not correct for one of the battery circuits at the ECM. 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 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.
Results:
- OK - The batteries pass the load test.
Repair: The batteries are OK. There is an open circuit or excessive resistance in the wiring or connections between the batteries and the ECM. Verify that the 20 Amp circuit breaker for the ECM is not tripped. Verify that the connections at the bus bars that are for the battery are clean and tight. Repair the connectors or wiring and/or replace the connectors or wiring between the battery and the J1/P1 ECM connector.
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 Voltage from the Keyswitch to the ECM
- 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 on terminal B of the keyswitch to the negative battery contact.
- Measure the voltage on terminal R of the keyswitch to the negative battery contact.
- Remove electrical power from the ECM.
- Turn the keyswitch to the OFF position.
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: There is a problem in the circuit that is between the keyswitch and the ECM. Repair the wiring and/or the connectors. Verify that the repair eliminates the problem.
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 that is 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