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

Illustration 1	g01238171
Schematic of the transmission oil temperature sensor

This diagnostic trouble code is associated with the transmission oil temperature sensor. The FMI 3 means that the ECU has determined that the voltage of the circuit for the sensor is above normal.

The possible causes of the diagnostic trouble code are listed:

• The energize circuit of the sensor is open.

• 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 177 FMI 3 is active before performing this procedure.

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

Test Step 1. CHECK THE VOLTAGE AT THE SENSOR.

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

2. Disconnect the sensor from the machine harness.

3. At the machine harness connector for the sensor, measure the voltage between contact 1 (wire 428-OR) and contact 2 (wire 202-BK).

Expected Result:

The voltage is approximately 5 VDC.

Results:

• OK - The voltage is approximately 5 VDC. Proceed to test step 5.

• NOT OK - The voltage is not approximately 5 VDC.

  Repair: There is a problem with the machine harness or the ECU has failed. It is unlikely that the ECU has failed.

  Proceed to test step 2.

Test Step 2. CHECK FOR AN OPEN IN THE SUPPLY CIRCUIT.

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

2. The sensor remains disconnected from the machine harness.

3. At the machine harness connector for the sensor, measure the voltage from contact 1 (wire 428-OR) to ground.

Expected Result:

The voltage is approximately 5 VDC.

Results:

• OK - The voltage measurement is approximately 5 VDC. Proceed to test step 3.

• NOT OK - The voltage does not measure approximately 5 DC.

  Repair: The supply circuit is not correct. Repair the circuit or replace the circuit.

  Proceed to Test Step 5.

Test Step 3. CHECK FOR AN OPEN IN THE RETURN CIRCUIT.

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

2. The sensor remains disconnected from the machine harness.

3. Disconnect the machine harness connector J1 from the ECU.

4. At the machine harness connector for the sensor, install a jumper wire from contact 2 (wire 202-BK) to ground.

5. At the machine harness connector for the ECU, measure the resistance from contact J1-21 (wire 202-BK) to ground.

Expected Result:

The resistance measurement is less than 5000 ohms.

Results:

• OK - The resistance measurement is less than 5000 ohms. The harness is correct.

  Repair: The sensor has failed. Replace the sensor.

  Proceed to Test Step 5.

• NOT OK - The resistance that is measured is not correct.

  Repair: There is an open in the machine harness. The open is in the return circuit with the high resistance measurement. Repair the harness or replace the harness.

  Proceed to Test Step 5.

Test Step 4. 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 1 (wire 428-OR).

4. Observe the status of the SPN 177 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 5.

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

  Repair: Replace the sensor. Verify that the new sensor corrects the problem.

  Proceed to Test Step 5.

Test Step 5. 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 fastened.

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

5. Operate the machine.

6. Determine if the SPN 177 FMI 3 is active.

Expected Result:

The SPN 177 FMI 3 is active.

Results:

• YES - The SPN 177 FMI 3 is active. The diagnostic trouble code has not been corrected.

  Repair: Check the circuit again. It is unlikely that the ECU has failed. Replace the sensor. If replacing the sensor does not correct the problem, 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 177 FMI 3 is not active. The diagnostic trouble code 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