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| Illustration 1 | g01363864 |
Schematic for the Left Drive Motor Speed Sensors | |
This diagnostic code is associated with the Left Drive Motor Speed Sensor #1. Each motor has two speed sensors, two signal wires, a power signal wire, and a ground. The ECM is able to diagnose each signal wire independently. Each signal wire provides a frequency input to the ECM that is proportional to motor speed. If this diagnostic code is active, the ECM will keep the code active until a good sensor signal is observed by the ECM. This means that the drive motors must be moved in order for the ECM to determine if the active code can be cleared.
This diagnostic code is recorded when the machine ECM receives an incorrect signal from the speed sensor. The incorrect signal will be erratic, intermittent, or incorrect.
The possible causes of this diagnostic code are listed:
- The supply circuit is open.
- The return circuit is open.
- The signal circuit is open.
- The signal circuit is shorted.
- Debris on the sensor
- The sensor has failed.
- The ECM has failed. This is unlikely.
Before performing this procedure, inspect the harness connectors that are involved in the circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all circuit connections are clean. Verify that all circuit connections are secure. Verify that all circuit connections are in good condition. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing this procedure.
System Response:
CID 2685 - FMI 02 will generate a level 2 warning. "Closed Loop Control" and "Unexpected Motor Speed Detection Control" will be disabled. While the machine is moving, a level 3 event will be active indicating that "Unexpected Motor Speed Detection" is disabled E695.
Note: The following test procedure may create other diagnostic codes. Clear the diagnostic codes when the problem has been corrected. Verify that CID 2685 - FMI 02 is active before performing this procedure.
Test Step 1. CHECK THE POWER AT THE SENSOR
- The machine harness remains disconnected from the sensor.
- Turn the key start switch to the ON position.
- At the machine harness for the sensor, measure the voltage. Measure the voltage from contact 1 (wire P769-YL) and contact 2 (wire P770-WH).
Expected Result:
The voltage that is measured is 8.0 ± 0.5 DCV.
Results:
- OK - The voltage measurement is 8.0 ± 0.5 DCV. Proceed to test step 2.
- NOT OK - The measurement is not correct.
Repair: Repair the harness or replace the harness. Verify that the diagnostic has been cleared. Drive the machine above the speed threshold. Verify that the diagnostic tool has been cleared.
STOP
Test Step 2. CHECK FOR AN OPEN SIGNAL CIRCUIT.
- Disconnect the negative battery cable and turn the key start switch to the OFFposition.
- Remove the connector from the speed sensor and place a jumper between pins 3 and 4.
- Disconnect J1 and J2 connectors from the ECM. Measure the continuity from pin J2-35 wire (834-YL) to pin J2-40 wire (835-GY).
Expected Result:
The resistance between pins 3 and 4 is less than 5Ω.
Results:
- OK - The resistance between pins 3 and 4 is less than 5Ω. Proceed to test step 3.
- NOT OK - The resistance between pins 3 and 4 is greater than 5Ω. There is an open circuit in one of the signal wires on the machine harness. The open circuit is in wire 834-YL or wire 835-BU.
Repair: Repair the machine harness or replace the machine harness. Verify that the diagnostic tool has been cleared. Drive the machine above the threshold for the motor speed.
Proceed to test step3.
Test Step 3. CHECK FOR A SHORT IN THE HARNESS.
- The machine harness remains disconnected from the sensor.
- Turn the key start switch to the OFF position.
- Disconnect the J1 and J2 machine harness connectors from the ECM.
- At machine harness connector J1 and J2, measure the resistance. Measure the resistance from the contact J2-35 (wire 834-YL) and contact J2-40 (wire 835-BU) of the machine harness to all contacts that are used in the machine harness connectors for the ECM.
Expected Result:
The resistance should be greater than 5000 ohms for each measurement.
Results:
- OK - The resistance is greater than 5000 ohms. The machine harness is correct. Proceed to test step 4.
- NOT OK - The resistance is NOT correct. There is a short in the machine harness. The short is between wire 835-BU and the circuit with the low resistance measurement or the short is between wire 834-YL and the circuit with the low resistance measurement.
Repair: Repair the harness or replace the harness. Verify that the diagnostic tool has been cleared. Drive the machine above the threshold for the motor speed.
STOP
Test Step 4. INSPECT THE SENSOR.
- The key start switch remains in the OFF position.
- The sensor remains disconnected from the machine harness.
- Remove the speed sensor. Inspect the speed sensor for damage.
- Clean the sensor with a lint free cloth.
Expected Result:
The sensor is not damaged. Reinstall the speed sensor.
Results:
- OK - The sensor is not damaged. The sensor is free of foreign material. Proceed to test step 5.
- NOT OK - The sensor is damaged.
Repair: Repair the sensor or replace the sensor. Verify that the diagnostic tool has been cleared. Drive the machine above the threshold for the motor speed.
STOP
Test Step 5. CHECK IF THE DIAGNOSTIC CODE REMAINS.
- Inspect the contacts and clean the contacts of the harness connectors.
- Reconnect all harness connectors.
- Turn the key start switch to the ON position.
- Clear all inactive diagnostic codes.
- Operate the machine.
Note: Movement of the machine will be required in order to clear this diagnostic code. The ground speed must be high enough to detect a motor speed signal.
- Stop the machine and place the parking brake switch in the ON position.
- Check if the diagnostic code for the sensor is active.
Expected Result:
The diagnostic code is NO longer active.
Results:
- OK - The diagnostic code is NO longer active. The diagnostic code does not exist at this time. The initial diagnostic 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
- NOT OK - The diagnostic code has not been corrected.
Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. Exit this procedure and perform this procedure again. If the cause of the diagnostic code is not found, contact your dealership's Technical Communicator for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacement, refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace"
STOP