D6N Track-Type Tractor Caterpillar

Illustration 1	g01766513
Thumb rocker position sensor connections

Illustration 2	g01930757
Location of the blade control handle

This diagnostic code is associated with the thumb rocker position sensor.

This diagnostic code is recorded when the Electronic Control Module (ECM) reads the pulse width modulated (PWM) signal voltage from the position sensor wire as being above normal.

Pull-up Voltage

For PWM sensor circuits, the ECM continuously outputs a pull-up voltage on the circuit for the sensor signal wire. When the ECM detects the presence of a voltage that is above a threshold on the signal circuit, the ECM will generate an FMI03 diagnostic code for the involved sensor.

For troubleshooting, when the sensor is disconnected from the machine harness, the presence of pull-up voltage at the sensor harness connector will indicate that the wires from the sensor connector to the ECM are OK. The absence of pull-up voltage at the sensor harness connector will indicate a possible open in the signal wire.

Possible causes of the diagnostic code are listed:

• The sensor power supply is open.

• The signal circuit is open or the sensor is disconnected.

• The signal circuit is shorted to a +battery source.

• The sensor has failed.

• The ECM has failed. An ECM failure is unlikely.

System Response:

When the ECM activates diagnostic code for the position sensor, the angle functions for the blade will not operate.

Note: Ensure that CID 1870 FMI 03 is active. This procedure can cause new diagnostic codes to be recorded. Ignore these created diagnostic codes. When the problem has been corrected, clear the created diagnostic codes.

Test Step 1. CHECK THE SUPPLY VOLTAGE AT THE SENSOR

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

2. The 12 contact connector for the sensor remains disconnected from the machine harness.

3. At the machine harness connector for the sensor, measure the voltage between contact "1" (wire 709-OR) and contact "2" (wire J765-BU).

Expected Result:

The voltage is approximately 10 VDC.

Results:

• OK - The voltage is approximately 10 VDC. Proceed to Test Step 2.

• NOT OK - The voltage measurement is not 10 VDC.

  Repair: There may be an open in the machine harness or the implement drive train fuse may be open. Check the fuse. Ensure that the fuse is not open. If the fuse is open, replace the fuse. Clear all diagnostic codes and check to see if the diagnostic code is still active. If the code is still active, perform this step again. If supply voltage is not present at the sensor connector, there is an open in the sensor supply circuit of the machine harness. Repair the machine harness or replace the machine harness.

  STOP

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

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

2. Disconnect the 12 contact machine harness connector from the sensor.

3. At the 12 contact machine harness connector for the sensor, measure the voltage from contact "3" (wire K757-YL) to contact "2" (wire J765-BU).

Expected Result:

If the signal circuit and the return circuit for the position sensor are correct, the ECM pull-up voltage should be indicated on the voltage measurement. The value of this voltage can vary. The presence of a voltage will indicate that the signal circuit is most likely not open. The absence of a voltage most likely will indicate an open in the signal circuit.

Results:

• OK - The pull-up voltage is present when the measurement is performed, indicating that the signal circuit and the return circuit are not open. Proceed to Test Step 3.

• NOT OK - Very little or no voltage is measured. There is an open or a bad connection in the return circuit or in the signal circuit of the sensor circuit.

  Repair: There is an open or a bad connection in the signal circuit or in the return circuit. Refer to the complete machine Electrical Schematic. Check all harness connectors that are in the position sensor circuit for corroded, loose, or broken contacts. Repair the machine harness or replace the machine harness.

  STOP

Test Step 3. CHECK THE SIGNAL CIRCUIT FOR A SHORT

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

2. The 12 contact connector for the position sensor remains disconnected from the machine harness.

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

4. At the "J1" and "J2" machine harness connectors for the ECM, measure the resistance of the sensor signal contact "J2-40" (wire K757-YL) to all other "J1" and "J2" contacts.

Expected Result:

Each resistance measurement should be greater than 5000 ohms.

Results:

• OK - Each resistance measurement is greater than 5000 ohms.

  Repair: The thumb rocker position sensor has failed. Replace the blade control handle. After replacement, calibrate the thumb rocker position sensor. Refer to Troubleshooting, KENR8558, "Implement Operator Control - Calibrate". Verify that the new handle has corrected the problem.

  If the replacement handle has not corrected the problem, proceed to Test Step4.

• NOT OK - One or more resistance measurements less than 5000 ohms.

  Repair: There is a short in the machine harness. The short is between the signal circuit and the circuit with the low resistance measurement. Repair the harness or replace the harness.

  STOP

Test Step 4. CHECK THE STATUS OF THE DIAGNOSTIC CODE

1. Inspect the contacts and clean the contacts of any harness connectors that are disconnected.

2. Reconnect all harness connectors.

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

4. Clear all inactive diagnostic codes.

5. Operate the machine.

6. Determine if the CID 1870 FMI 03 diagnostic code is active.

Expected Result:

The CID 1870 FMI 03 diagnostic code is active.

Results:

• YES - The CID 1870 FMI 03 diagnostic code is active. The problem has not been corrected.

  Repair: Check the sensor circuit again. Use the Caterpillar Electronic Technician (Cat ET) service tool in order to perform a wiggle test on the machine wiring harness. The wiggle test can detect momentary or intermittent shorts or opens in the machine wiring harness.If the cause of the problem is not found, the ECM may have failed. Prior to replacing an ECM, always contact the technical communicator at your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the cause of the diagnostic code is not found and the ECM must be replaced, refer to the Troubleshooting, "Electronic Control Module (ECM) - Replace" Section of this manual for details.

  STOP

• NO - The CID 1870 FMI 03 diagnostic code is not active. The problem does not exist at this time.

  Repair: The initial diagnostic code may have been caused by a poor electrical connection that was corrected when a harness connector was disconnected and reconnected. Resume normal machine operation.

  STOP