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| Illustration 1 | g01363864 |
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Simplified schematic of the Left Drive Motor Speed Sensors | |
This diagnostic code is associated with the Left Drive Motor Speed Sensor #2. 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 motor speed sensor. The incorrect signal that is being read by the machine ECM has the following characteristics: Abnormal frequency, pulse width, or period
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. ECM failure is unlikely.
Poor connections can often be the cause of a problem in an electrical circuit. Before performing this procedure, inspect the harness connectors that are involved in the circuit. · Verify that all connections are clean. · Verify that connections are secure. · Verify that all connections are in good condition. If a problem with a connection is found, correct the problem and ensure that this diagnostic code is active before performing this procedure.
Reference: Testing and Adjusting, "Electrical Connector - Inspect" in this manual.
System Response:
CID 2686 FMI 08 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.
Troubleshooting:
Note: The following test procedure may create other diagnostic codes. Clear the diagnostic codes when the problem has been corrected. Verify that (CID 2686 FMI 08) is active before performing this procedure.
Test Step 1. CHECK THE POWER AT THE SENSOR
Note: If a CID 41 (8 Volt DC Supply) diagnostic code was logged, proceed to that testing procedure.
- 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(Yellow)) and contact 2 wire (P770-WH(White)).
Expected Result:
The voltage that is measured is 8.0 ± 0.5 DCV.
Results:
- YES - The voltage measurement is 8.0 ± 0.5 DCV. Proceed to test step 2.
- NO - The voltage is not correct.
Repair: Repair 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 OFF position.
- Remove the connector from the speed sensor and place a jumper between pins 3 and 4.
- Disconnect connectors J1 and J2 from the ECM and then measure the continuity between pins J2 35 wire (834-YL(Yellow)) and J2 40 wire (835-PU(Purple)).
Expected Result:
The resistance between pins 3 and 4 is less than 5 ohms.
Results:
- YES - The resistance between pins 3 and 4 is less than 5 ohms. Proceed to test step 3.
- NO - The resistance between pins 3 and 4 is greater than 5 ohms. There is an open circuit in one of the signal wires on the machine harness. The open is in wire (8342-YL(Yellow)) or wire (834-YL(Yellow)). The machine harness has failed.
Repair: Repair or replace the machine harness. Verify that the diagnostic tool has been cleared. Drive the machine above the threshold for the motor speed.
STOP
Test Step 3. CHECK FOR A SHORTED SIGNAL CIRCUIT
- The key start switch remains in the OFF position.
- Remove the jumper between pins 3 and 4 from the speed sensor connector.
- At the J2 connector, measure the resistance between contact pin J2 35 wire (834-YL(Yellow)) and all the other contacts that are used in the J1 and J2 ECM harness connectors.
- At the J2 connector, measure the resistance between contact pin J2 40 wire (835-PU(Purple)) and all the other contacts that are used in the J1 and J2 ECM harness connectors.
Expected Result:
Every resistance measurement is more than 5 ohms.
Results:
- YES - Every resistance measurement is more than 5 ohms. Proceed to test step 4.
- NO - Every resistance measurement is not more than 5 ohms. There is a short circuit in one of the signal wires on the machine harness. The short is to the wire with more than 5 ohms resistance. The machine harness has failed.
Repair: Repair or replace the machine 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 lint free cloth.
Expected Result:
The sensor is not damaged.
Results:
- YES - The sensor is not damaged. Proceed to test step 5.
- NO - The sensor is damaged or the presence of a foreign material exists.
Repair: Remove the foreign material and/or replace the sensor. 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 5. CHECK IF THE DIAGNOSTIC CODE REMAINS
- Inspect the contacts and clean the contacts of the harness connectors.
Reference: Testing and Adjusting, "Electrical Connector - Inspect" in this manual.
- Reconnect all harness connectors.
- Reconnect the negative battery cable and turn the key start switch to the ON position.
- Clear all inactive diagnostic codes.
- Operate the machine. Verify that the diagnostic has been cleared. Drive the machine above the speed threshold. Verify that the diagnostic tool has been cleared.
- 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:
- YES - 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 that was resolved when a connector was disconnected and reconnected. Resume normal machine operation.
STOP
- NO - The diagnostic code has not been corrected.
Repair: ECM failure is unlikely. Perform this procedure again. If no problems can be found, replace the sensor (if not previously replaced). If the cause of the diagnostic code still is not found, contact your dealer Technical Communicator (TC) for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM replacement is needed, refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace" in this manual.
STOP