CX28 Transmission For Combat and Tactical Vehicles Transmission ; Transfer Case Electronic Control System Caterpillar

Illustration 1	g01443191
Schematic of the oil level sensor for the transmission

This diagnostic trouble code is associated with the transmission oil temperature sensor. The FMI 4 means that the ECU has determined that the voltage of the circuit for the temperature sensor is below normal.

The possible causes of this diagnostic trouble code are listed below:

• The signal circuit for the sensor is shorted to ground.

• The sensor has failed.

• The ECU has failed. The ECU failing is unlikely.

Note: The following test procedure may create other diagnostic trouble codes. Ignore these created diagnostic trouble codes and clear the diagnostic trouble codes when the original diagnostic trouble code has been corrected. Ensure that the diagnostic trouble code of SPN 3027 FMI 4 is active before performing this procedure.

Note: Use a digital multimeter for the measurements in this procedure.

Test Step 1. INSPECT THE SENSOR.

1. Perform a visual inspection of the sensor, the wiring for the sensor and the hardware that is associated with the sensor.

Expected Result:

There is no apparent damage to the sensor, the wiring for the sensor or the hardware that is associated with the sensor.

Results:

• OK - There is no apparent damage to the sensor, the wiring for the sensor or the hardware that is associated with the sensor. Proceed to Test Step 2.

• NOT OK - There is apparent damage to the sensor, the wiring for the sensor or the hardware that is associated with the sensor.

  Repair: Replace the damaged part.

  Proceed to Test Step 2.

Test Step 2. CHECK THE SENSOR.

1. Disconnect the harness connector from the sensor.

2. Monitor the status of the diagnostic trouble code.

Expected Result:

The diagnostic trouble code changes from an FMI 4 to an FMI 3.

Results:

• YES - The FMI 4 does not change to an FMI 3. The harness and the ECU are correct. The sensor is faulty.

  Repair: Replace the sensor.

  STOP

• NO - The diagnostic trouble code is no longer active. A problem exists in the harness or the ECU. It is unlikely that the ECU has failed. Proceed to Test Step 3.

Test Step 3. CHECK THE SIGNAL CIRCUIT FOR A SHORT IN THE HARNESS.

1. The key start switch and the disconnect switch remain in the OFF position.

2. Disconnect the machine harness connectors from the sensor and the ECU.

3. Measure the resistance between contact J1-36 (wire 425-PK) and all of the contacts that are used in the machine harness connectors for the ECM.

Expected Result:

Each resistance measurement is greater than 5000 ohms.

Results:

• OK - Each of the resistance measurements are greater than 5000 ohms. The circuit is correct. Proceed to Test Step 4.

• NOT OK - The resistance is less than 5 ohms. The signal circuit is shorted to another circuit in the harness.

  Repair: Repair the machine harness or replace the machine harness.

  STOP

Test Step 4. CHECK IF THE DIAGNOSTIC TROUBLE CODE IS STILL ACTIVE.

1. Inspect the harness connectors. Clean the contacts of the harness connectors and check the wires for damage to the insulation that is caused by excessive heat, battery acid, or chafing.

2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit.

3. Reconnect all harness connectors in order to make sure that the connectors are fully seated. Also, make sure that the clips for each connector are completely fastened.

4. Turn the disconnect switch and the key start switch to the ON position.

5. Operate the machine.

6. Determine if the SPN 3027 FMI 4 is active.

Expected Result:

The SPN 3027 FMI 4 is active.

Results:

• YES - The SPN 3027 FMI 4 is active. The problem has not been corrected.

  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 ECU, 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

• NO - The SPN 3027 FMI 4 is not active. The problem does not exist at this time. The initial diagnostic trouble code was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.STOP