Use this procedure to troubleshoot the electrical system if a problem is suspected with the power to the engine's Electronic Control Module (ECM) or if any one of the diagnostic codes in Table 1 is active or easily repeated. Refer to Troubleshooting, "Event Code List" for information about event codes and the default trip points for these codes. You must access the monitoring system on Caterpillar Electronic Technician (ET) in order to view the current trip points for these codes.
| Diagnostic Codes Table | ||
|---|---|---|
| Description | Conditions which Generate this Code | System Response |
| E043(1) Low System Voltage Warning | The battery voltage to the ECM is less than normal. | The code is logged. |
| 168-0 Electrical System Voltage high | The battery supply voltage is greater than 32 VDC for two seconds. The engine's ECM has been powered for three seconds. The engine is not being cranked. |
|
| 168-1 Electrical System Voltage low | The battery supply voltage is less than 9 VDC for two seconds. The engine's ECM has been powered for three seconds. The engine is not being cranked. |
|
| 168-2 Electrical System Voltage erratic, intermittent, or incorrect | The engine is running but not cranking. The battery voltage falls below 9 VDC for at least .06 seconds. The voltage returns above 9 VDC. or Three voltage readings in the last seven seconds were below 9 VDC. |
|
To reduce resistance in the wiring harness, there are two isolated power connections to the ECM. The connections must be complete in order to ensure proper engine operation. There may always be a constant power supply to the ECM when the engine is shutdown. In order to shut off the power to the ECM, the breaker for the ECM must be turned to the OFF position and the switch that supplies keyswitch power to the ECM must be in the OFF position.
The engine will begin the start-up when the following conditions exist:
- Battery voltage is present at the two +Battery inputs on the ECM.
- The ECM detects voltage at the input for the keyswitch.
- The emergency stop switch is not activated.
- The start/run/stop switch is in the RUN position.
When the start/run/stop switch is activated the inputs to the ECM from the start/run/stop switch go low.
When the emergency stop push button is activated, the emergency stop inputs float high. The fuel supply to the injectors will be cut off and the air shutoff relays will be activated.
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| Illustration 1 | g01265628 |
Typical schematic | |
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| Illustration 2 | g01258369 |
P1 ECM connector (P1-52) +Battery (P1-53) +Battery (P1-63) −Battery (P1-65) −Battery (P1-70) Keyswitch | |
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| Illustration 3 | g01265629 |
Machine interface connector (Terminal 1) +Battery (Terminal 2) +Battery (Terminal 34) −Battery (Terminal 35) −Battery (Terminal 26) Keyswitch | |
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| Illustration 4 | g01234146 |
Location of ECM connectors | |
Test Step 1. Inspect Electrical Connectors and Wiring
- Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.
- Turn the breaker for the ECM to the OFF position.
- Thoroughly inspect the ECM connectors J1/P1. Inspect all of the other connectors. Refer to Troubleshooting, "Inspecting Electrical Connectors" for the proper procedure for inspecting system wiring.
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
- Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Inspecting Electrical Connectors" for details.
- Check the harness and the wiring for abrasion and for pinch points.
Expected Result:
All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.
Results:
- OK - The harness and wiring are 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
- Measure no-load voltage at the battery posts. Refer to Systems Operation/Testing and Adjusting for the proper procedures to check the batteries.
- Load test the batteries. Use the 4C-4911 Battery Load Tester. Refer to the Operating Manual, SEHS9249. Refer to Special Instruction, SEHS7633.
Expected Result:
The no-load voltage at the batteries is at least 23.5 VDC, and the batteries pass the load test.
Results:
- OK - The no-load voltage at the batteries is at least 23.5 VDC, and the batteries pass the load test. Proceed to Test Step 3.
- Not OK - The no-load voltage at the batteries is less than 23.5 VDC, and/or the batteries fail the load test.
Repair: The batteries or the alternator are causing the problem. Recharge the batteries or replace the batteries. Verify that the original condition is resolved. Refer to Systems Operation/Testing and Adjusting for information on the charging system.
STOP
Test Step 3. Check the Voltage at the ECM Connector
- Disconnect the J1/P1 ECM connector.
- Turn the breaker for the ECM to the ON position.
- Turn the switch that provides power to the keyswitch input for the ECM to the ON position.
- Wiggle the harness during the following test steps in order to find an intermittent condition.
- Measure the voltage between P1-52 (positive battery) and P1-63 (negative battery).
- Measure the voltage between P1-53 (positive battery) and P1-65 (negative battery).
- Measure the voltage between P1-70 (keyswitch) and P1-65 (negative battery).
- Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.
- Turn the breaker for the ECM to the OFF position.
Expected Result:
The voltage is ± 1 VDC from the voltage at the battery terminals.
Results:
- OK - The ECM is receiving the correct voltage.
Repair: If an intermittent condition is suspected, refer to Troubleshooting, "Inspecting Electrical Connectors".
STOP
- Not OK - The voltage is not ± 1 VDC from the voltage at the battery terminals. Proceed to Test Step 4.
Test Step 4. Check the Voltage at the Machine Interface Connector
- Disconnect the machine interface connector.
- Turn the breaker for the ECM to the ON position.
- Turn the switch that provides power to the keyswitch input for the ECM to the ON position.
- Wiggle the harness during the following test steps in order to find an intermittent condition.
- Measure the voltage between Terminal 1 (positive battery) and Terminal 34 (negative battery) at the machine interface connector.
- Measure the voltage between Terminal 2 (positive battery) and Terminal 35 (negative battery) at the machine interface connector.
- Measure the voltage between Terminal 26 (keyswitch) and Terminal 34 (negative battery) on the machine interface connector.
- Turn the switch that provides power to the keyswitch input for the ECM to the OFF position.
- Turn the breaker for the ECM to the OFF position.
Expected Result:
The voltage is ± 1 VDC from the voltage at the battery terminals.
Results:
- OK - The voltage is correct at the machine interface connector.
Repair: The problem is in the wiring and/or connectors between the machine interface connector and the ECM. Use continuity checks in order to find the open or short in the circuitry.
STOP
- Not OK - The voltage is not ± 1 VDC from the voltage at the battery terminals.
Repair: There is a problem in the customer's wiring to the machine interface connector. All connectors, pins, and sockets should be completely coupled and/or inserted. The harness and wiring should be free of corrosion, of abrasion, and of pinch points.
STOP