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 oil level sensor for the transmission. The FMI 3 means that the ECU has determined that the voltage of the sensor is above 4.8 ± 0.04 VDC.

The possible causes of the diagnostic trouble code are listed:

• The energize circuit of the sensor is shorted to the +battery circuit.

• 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 these diagnostic trouble codes when the original diagnostic trouble code has been corrected. Ensure that the diagnostic trouble code of SPN 3027 FMI 3 is active before performing this procedure.

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

Note: The ECU reads a voltage of 0.3 VDC if the sensor loses the power connection to the 5 VDC. The ECU reads a voltage of 5.4 VDC if the sensor loses the connection to ground. The output is 4.5 VDC when the sensor is completely immersed in fluid.

Test Step 1. CHECK THE SENSOR.

1. Turn the disconnect switch and the key start switch to the ON position. Do not start the engine.

2. Disconnect the sensor with the active diagnostic trouble code from the machine harness.

3. At the machine harness connector for the sensor, place a jumper wire from contact 2 (wire 202-BK) to contact 3 (wire 425-PK).

4. Observe the status of the SPN 3027 FMI 3.

Expected Result:

The diagnostic trouble code changes from FMI 3 to FMI 4 as the jumper wire is installed.

Results:

• YES - The diagnostic trouble code remains active. The jumper wire does not affect the diagnostic trouble code. Proceed to Test Step 2.

• NO - The diagnostic is no longer active. The sensor has failed.

  Repair: Replace the sensor.

  STOP

Test Step 2. CHECK THE ENERGIZE CIRCUIT OF THE SENSOR FOR A SHORT TO THE +BATTERY CIRCUIT.

1. Turn the key start switch and the disconnect switch to the OFF position.

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

3. At the machine harness connector for the ECU, measure the resistance from contact J1-36 (wire 709-OR) to all contacts that are used in the machine harness connectors for the ECU.

Expected Result:

Each resistance measurement is greater than 5000 ohms.

Results:

• OK - Each resistance measurement is greater than 5000 ohms. The machine harness is correct. Proceed to Test Step 3.

• NOT OK - Each resistance measurement is not greater than 5000 ohms. There is a short in the machine harness. The short is between J1-36 (709-OR) and the circuit that has a low resistance measurement.

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

  STOP

Test Step 3. 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 vehicle.

6. Determine if the SPN 3027 FMI 3 is active.

Expected Result:

The SPN 3027 FMI 3 is active.

Results:

• YES - The SPN 3027 FMI 3 is active. The problem has not been corrected.

  Repair: Check the circuit again. 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 3 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 vehicle operation.STOP