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| Illustration 1 | g01249620 |
Schematic of the 5 volt sensor supply | |
The 5 volt power supply provides power to the oil level sensor for the transmission. The FMI 4 is recorded when the ECU reads the voltage of the signal wire as being below normal and/or shorted to ground.
The following is a list of possible causes for this diagnostic trouble code:
- The sensor supply circuit is shorted to the ground.
- A sensor has failed.
- The ECU has failed. This is unlikely.
Note: The following test procedure may create other diagnostic trouble codes. Ignore these created diagnostic trouble codes and clear these diagnostic trouble codes when the original diagnostic trouble code has been corrected. Ensure that the diagnostic trouble code of SPN 3509 FMI 4 is active before performing this procedure.
Note: Use a digital multimeter for the measurements in this procedure.
Test Step 1. CHECK THE SENSOR
- Turn the key start switch and the disconnect switch to the ON position.
- Disconnect the machine harness from the sensor. Then, observe the status of the diagnostic trouble code.
Expected Result:
The diagnostic trouble code is not active.
Results:
- OK - The diagnostic trouble code is not active. The harness circuit is correct. The sensor that was just disconnected has failed.
Repair: Replace the sensor.
STOP
- NOT OK - The diagnostic trouble code is still active. The machine harness may be shorted to ground. Proceed to Test Step 2.
Test Step 2. CHECK FOR A SHORT TO GROUND
- Turn the key start switch and the disconnect switch to the OFF position.
- Disconnect the machine harness from the ECU.
- At the harness connector for the ECU, measure the resistance between frame ground and contact J1-11 (wire 709-OR) of the sensor 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 may have failed.
Repair: Check the circuit again. If the Caterpillar Electronic Technician (ET) is available, use the Cat ET service tool in order to perform a "Wiggle Test" on the machine wiring harness. The "Wiggle Test" can detect shorts and opens in the machine wiring harness that are momentary or intermittent. 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 ECM, always contact your dealership 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. The machine harness has failed.
Repair: The 709-OR wire is shorted to ground in the machine harness. Refer to the complete Electrical System Schematic for your machine. Check all harness connectors that are in the power supply circuit. Ensure that the connectors are clean and secure. Repair the machine harness or replace the machine harness.
STOP