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| Illustration 1 | g01248848 |
Schematic of the +8V Sensor Supply | |
This diagnostic trouble code is recorded when the ECU reads the voltage of the 8 volt DC supply circuit (wire 709-OR) and the voltage is below normal.
Note: Use a digital multimeter for the measurements in this procedure.
System Response:
Components that receive power from the 8 volt DC supply will not be available.
Test Step 1. CHECK THE VOLTAGE AT THE ECU.
- Turn the disconnect switch and the key start switch to the ON position.
- Check the voltage at the connector of the ECU from contact J1-44 (8 volt DC supply) to contact J2-22 (sensor ground). Use the cable probes to measure the voltage. Do NOT disconnect the machine harness from the ECU.
Expected Result:
The voltage is 8.0 ± 0.5 DCV.
Results:
- OK - The voltage is 8.0 ± 0.5 DCV. The 8 volt DC supply voltage is correct. Verify that the diagnostic trouble code is present. If the diagnostic trouble code is still present the ECU has failed. Proceed to Test Step 2.
- NOT OK - Voltage is NOT 8.0 ± 0.5 DCV. The voltage is less than 8.0 ± 0.5 DCV. The ECU has failed.
Repair: Check the circuit again. Use the Caterpillar Electronic Technician (ET) service tool, if available, in order to perform a "Wiggle Test" on the machine wiring harness. The wiggle test can detect momentary or intermittent shorts or opens in the machine wiring harness. It is unlikely that the ECU has failed. Exit this procedure and perform this procedure again. If the cause of the diagnostic trouble code is not found, replace the ECU. Prior to replacing an ECU, always contact your dealership's Technical Communicator for possible consultation with Caterpillar. This consultation may greatly reduce repair time. See Testing and Adjusting, "Electronic Control Unit - Replace".
STOP
Test Step 2. CHECK FOR A SHORT TO GROUND.
- Disconnect any sensor that uses the 8 volt DC supply voltage from the machine harness.
- At the harness connector for the ECU, measure the resistance between frame ground and contact J1-44 of the 8 volt DC supply circuit.
Expected Result:
The resistance is greater than 5000 ohms.
Results:
- OK - The resistance is greater than 5000 ohms. The harness circuit resistance is correct. The ECU has failed.
Repair: Check the circuit again. Use the Caterpillar Electronic Technician (ET) service tool, if available, in order to perform a "Wiggle Test" on the machine wiring harness. The wiggle test can detect momentary or intermittent shorts or opens in the machine wiring harness. It is unlikely that the ECU has failed. Exit this procedure and perform this procedure again. If the cause of the diagnostic trouble code is not found, replace the ECU. Prior to replacing an ECU, always contact your dealership's Technical Communicator for possible consultation with Caterpillar. This consultation may greatly reduce repair time. See Testing and Adjusting, "Electronic Control Unit - Replace".
STOP
- NOT OK - The resistance is less than 5000 ohms. If the resistance is less than 5000 ohms with all the sensors disconnected from the machine harness. The machine harness is shorted to ground. Proceed to Test Step 3.
Test Step 3. DISCONNECT THE SENSOR(S).
- Turn the key start switch and the disconnect switch to the ON position.
- After disconnecting the sensor(s), check the Caterpillar Electronic Technician (ET) for any active diagnostic trouble codes.
Expected Result:
The diagnostic trouble code changes from a FMI 04 to a FMI 03.
Results:
- OK - The diagnostic trouble code changes to an FMI 03. There is an internal failure in the handle. The handle has failed
Repair: Replace the handle.
STOP
- NOT OK - The diagnostic trouble code does not change to an FMI 03. The ECU has failed.
Repair: Check the circuit again. Use the Caterpillar Electronic Technician (ET) service tool, if available, in order to perform a "Wiggle Test" on the machine wiring harness. The wiggle test can detect momentary or intermittent shorts or opens in the machine wiring harness. It is unlikely that the ECU has failed. Exit this procedure and perform this procedure again. If the cause of the diagnostic trouble code is not found, replace the ECU. Prior to replacing an ECU, always contact your dealership's Technical Communicator for possible consultation with Caterpillar. This consultation may greatly reduce repair time. See Testing and Adjusting, "Electronic Control Unit - Replace".
STOP