279C, 279C2, 289C, 289C2 and 299C Compact Track Loaders, 287C, 277C, 277C2, 287C2 and 297C Multi Terrain Loaders and 246C, 256C, 262C, 262C2 and 272C Skid Steer Loaders Machine Electronic Control System Caterpillar

Illustration 1	g01365487
Schematic for the Right Drive Motor Speed Sensors

This diagnostic code is associated with the Right Drive Motor Speed Sensor #2. each sensor has two signal wires and a power ground wire. 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 signal is obtained. 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 that is being read by the machine ECM has the following characteristics: 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. 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 connections in the circuit are clean. Verify that all connections in the circuit are secure. Verify that all connections in the circuit 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 2688 - 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.

Note: The following test procedure may create other diagnostic codes. Clear the diagnostic codes when the problem has been corrected. Verify that CID 2688 - FMI 08 is active before performing this procedure.

ReferenceSpecifications, "Hydrostatic Motor and Mounting" and SMCS 4803 - WHEEL SPEED SENSOR

Test Step 1. CHECK POWER AT THE SENSOR

1. Disconnect the sensor from the machine harness.

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

3. 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 measurement is 8.0 ± 0.5 VDC.

Results:

• OK - The voltage measurement is 8.0 ± 0.5 VDC. 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.

1. Disconnect the negative battery cable and turn the key start switch to the OFF position.

2. Remove the connector from the speed sensor and place a jumper between pins 3 and 4.

3. Disconnect J1 and J2 from the ECM and then measure the continuity between pins J2-41 wire (832-BR) and J2-42 wire (833-GY).

Expected Result:

The resistance between pins 3 and 4 is less than 5 ohms.

Results:

• OK - The resistance between pins 3 and 4 is less than 5Ω. Proceed to test step 4.

• NOT OK - 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 circuit is in wire (832-BR) or wire (833-GY). The machine harness or the ECM has failed.

  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 step 3.

Test Step 3. CHECK FOR A SHORT IN THE HARNESS.

1. The machine harness remains disconnected from the sensor.

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

3. Disconnect the J1 and J2 machine harness connectors from the ECM.

4. At machine harness connector J1 and J2, measure the resistance. Measure the resistance from the contact J2-41 wire (832-BR) and contact J2-42 wire (833-GY) 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 (833-GY) and the circuit with the low resistance measurement or the short is between wire (832-BR) 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 AND HARNESS

1. The key start switch remains in the OFF position.

2. The sensor remains disconnected from the machine harness.

3. Inspect the speed sensor harness for damage.

4. Remove the speed sensor. Inspect the speed sensor for damage.

5. Clean the sensor with a lint free cloth.

Expected Result:

The sensor and harness are not damaged.

Results:

• OK - The sensor and harness are not damaged. Proceed to test step 5.

• NOT OK - The sensor or harness is damaged. Verify that the diagnostic tool has been cleared. Drive the machine above the threshold for the motor speed.

  Repair: Repair the sensor/harness or replace the sensor/harness.

  STOP

Test Step 5. CHECK IF THE DIAGNOSTIC CODE REMAINS.

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

   Refer to Testing and Adjusting, "Electrical Connector - Inspect" in this manual

2. Reconnect all harness connectors.

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

4. Clear all inactive diagnostic codes.

5. Operate the machine.

   Note: Verify that the diagnostic tool has been cleared. Drive the machine above the threshold for the motor speed.

6. Stop the machine and place the parking brake switch in the ON position.

7. 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: Replace the speed sensor. If the cause of the problem is not found, contact the Technical Communicator for your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacement, see Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP