793F Series AC Off-Highway Truck/Tractor Braking System Caterpillar

Illustration 1	g02731146
Schematic of the "Left Final Drive Pressure" sensor

This diagnostic code is associated with the "Left Final Drive Pressure" sensor. The FMI 03 diagnostic code means that the Brake ECM has determined that the voltage of the circuit for the sensor is above normal. Refer to Systems Operation, "Sensors" for information regarding the operation of the sensor and the location.

The pressure sensor is a PWM sensor that uses a frequency of the approximately 500 Hz. The duty cycle operates from a range of 10% to 90%.

The possible causes of this diagnostic code are listed below:

• The signal circuit for the sensor is open.

• The signal circuit for the sensor is shorted to the +battery circuit.

• The sensor has failed.

• The power circuit or the ground circuit has failed.

• The Brake ECM has failed. This situation is unlikely.

Note: The following test procedure may create other diagnostic codes. Ignore these created diagnostic codes and clear the diagnostic codes when the original diagnostic code has been corrected. Ensure that the diagnostic code of CID 3021 FMI 03 is active before performing this procedure.

Note: Use the 146-4080 Digital Multimeter for the measurements in this procedure.

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When it is necessary to work under the machine with the body (bed) raised, attach the body (bed) retaining cables to the rear tow points. Install the rear tow point pins through the ends of the retaining cables. Failure to properly secure the body (bed) may result in personal injury or death.

Test Step 1. CHECK FOR POWER AT THE SENSOR.

1. Do not disconnect the harness connector from the sensor.

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

3. At the back of the harness connector for the sensor, insert a 7X-1710 Multimeter Probe along the voltage supply wire at contact A (wire A700-OR(Orange)).

4. Measure the voltage from contact A to frame ground.

Expected Result:

The voltage is 8 VDC.

Results:

• OK - The voltage is 8 VDC. Proceed to Test Step 2.

• NOT OK - The voltage is not 8 VDC. The +battery circuit in the machine harness has failed.

  Repair: Replace or repair the machine harness.

  STOP

Test Step 2. CHECK FOR PROPER GROUND AT THE SENSOR.

1. The machine harness remains connected to the sensor.

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

3. Remove the 7X-1710 Multimeter Probe from the voltage supply (wire A700-OR(Orange)).

4. At the back of the harness connector for the sensor, insert a 7X-1710 Multimeter Probe along the ground wire at contact B (wire C243-BK(Black)).

5. Measure the resistance from contact B to frame ground.

Expected Result:

The resistance is less than 5 ohms.

Results:

• OK - The resistance is less than 5 ohms. The ground circuit is correct. Proceed to Test Step 3.

• NOT OK - The resistance is greater than 5000 ohms. The ground circuit in the machine harness has failed.

  Repair: Replace or repair the machine harness.

  STOP

Test Step 3. CHECK THE WIRING HARNESS OF THE SENSOR FOR AN OPEN CIRCUIT.

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

2. Disconnect the machine harness from the sensor.

3. At the harness connector for the sensor, connect a jumper wire between contact B (wire C243-BK(Black)) and contact C (wire H919-OR(Orange)).

4. Disconnect the machine harness connectors from the Brake ECM.

5. At the harness connector for the ECM, measure the resistance between contact J2-43 (wire H919-OR(Orange)) and contact J1-45 (wire C243-BK(Black)).

Expected Result:

The resistance measurement is less than 5 ohms.

Results:

• OK - The resistance measurement is less than 5 ohms. The circuit is correct. Proceed to Test Step 4.

• NOT OK - The resistance is greater than 5000 ohms. The circuit is not correct. There is an open circuit in the wiring harness.

  Repair: There is an open circuit in the wiring harness. Repair or replace the wiring harness.

  STOP

Test Step 4. CHECK THE WIRING HARNESS OF THE SENSOR FOR A SHORT TO THE +BATTERY CIRCUIT.

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

2. The machine harness remains disconnected from the sensor. Remove the jumper wire that was installed in the previous step.

3. The machine harness connectors remain disconnected from the Brake ECM.

4. At the machine harness connector for the ECM, measure the resistance from the signal contact J2-43 (wire H919-OR(Orange)) of the machine harness to all contacts that are used in the machine harness connectors for the Brake ECM.

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 5.

• NOT OK - One or more resistance measurements are not correct. There is a short in the machine harness.

  Repair: The short is between signal contact J2-43 (wire H919-OR(Orange)) and the circuit with the low resistance measurement. Repair or replace the machine harness.

  STOP

Test Step 5. CHECK THE OUTPUT OF THE SENSOR.

1. Reconnect the machine harness connectors to the Brake ECM. Reconnect the machine harness connector to the sensor.

2. At the back of the harness connector for the sensor, insert a 7X-1710 Multimeter Probe along the signal wire (contact C).

3. At the back of the harness connector for the sensor, insert a 7X-1710 Multimeter Probe along the ground wire (contact B).

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

5. Measure the signal of the sensor. The proper signal is described at the beginning of this procedure.

Expected Result:

The signal from the sensor is valid.

Results:

• OK - The signal from the sensor is valid. Proceed to Test Step 6.

• NOT OK - The signal from the sensor is not valid.

  Repair: The sensor has failed. Replace the sensor.

  STOP

Test Step 6. CHECK IF THE DIAGNOSTIC CODE REMAINS.

1. Inspect the contacts of the harness connectors and clean the connectors.

2. Reconnect all harness connectors.

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

4. Operate the machine.

5. Check the status of the CID 3021 FMI 03 diagnostic code.

Expected Result:

The CID 3021 FMI 03 diagnostic code is active.

Results:

• YES - The CID 3021 FMI 03 diagnostic code is active. The diagnostic code has not been corrected. The ECM may have failed.

  Repair: A failure of the Brake ECM is unlikely. Exit this procedure and perform this procedure again. Prior to replacing an ECM, always contact the Technical Communicator your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the Brake ECM requires replacement, refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP

• NO - The CID 3021 FMI 03 diagnostic code is not active. The diagnostic code does not exist at this time.

  Repair: The initial diagnostic code was probably caused by a poor electrical connection at one of the harness connectors. Resume normal machine operation.

  STOP