120M Series 2, 12M Series 2, 140M Series 2 and 160M Series 2 Motor Graders Power Train Electronic Control System Caterpillar

Illustration 1	g02316933
Connections for "Steer Sensor 2"

Three steering position sensors are required for correct operation of the steering control. The steering position sensors are located in the assembly of the left joystick. Each sensor provides an input signal to the Implement ECM 2 and to the "Transmission/Chassis ECM". This diagnostic code is activated when the ECM reads the input signal from the "Steering Position Sensor 2" and the signal is erratic or intermittent.

The "Steering Position Sensor 2" receives power from the 8 VDC power supply of the Implement ECM 2. "Steering Position Sensor 2" is internally connected to the ground that is supplied by the 8 VDC sensor return of the "Transmission/Chassis ECM" (ground of the ECM) and the Implement ECM 2 (ground of the ECM). The steering sensor must lose both grounds in order to lose a ground connection. The illustration above indicates the power and ground connections for the "Steering Sensor 2".

The position sensor is a PWM sensor that operates at a frequency of approximately 500 Hz. The position sensor sends a PWM input signal to the Implement ECM 2 and to the "Transmission/Chassis ECM". The duty cycle of the signal will vary from 10 ± 5% at the full left position of the joystick to 90 ± 5% at the full right position of the joystick. When the joystick is in the center position, the duty cycle will be approximately 50%.

The possible causes of this diagnostic code are listed below:

• The sensor has failed.

• An Intermittent connection exists in the sensor circuit.

• The signal circuit is shorted to another circuit in the machine harness.

• The ECM has failed. A failure of the Transmission/Chassis ECM is unlikely.

Consider the following points when this code is active:

• If a CID 0041 diagnostic code for the 8 VDC power supply is active (MID 145 CID 0041), investigate and fix the problem before proceeding.

• The Transmission/Chassis ECM (MID 027) and the Implement ECM 2 (MID 145) receive an input signal from the "Steering Sensor 2". Both ECM modules can activate a CID 1472 FMI 02 diagnostic code when the signal is erratic or intermittent.

• When one of the ECM modules has activated a CID 1472 FMI 02 diagnostic code and the other ECM module has not, the probability is likely that the sensor is operating correctly. When this occurs, a poor connection in the machine harness would be suspected.

• When both ECM modules have activated the diagnostic code, either the sensor or a harness problem could be the cause.

• If both ECM modules have activated the diagnostic code, either ECM is probably not the cause of the problem.

• For either condition, proceed with this procedure in order to verify the cause of the problem.

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, that all connections are secure and that all 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.

Use Cat ET to discover the version of software that is installed on the ECM. Confirm that the latest version of software is installed on the ECM.

Note: Use Cat ET to determine if the CID 1472 FMI 02 diagnostic code exists for both ECM modules. If the fault exists for both ECM modules, then check the entire power supply circuit of the sensor before proceeding with this troubleshooting procedure.

Test Step 1. USE CAT ET TO CHECK FOR SIMILAR DIAGNOSTIC CODES

1. Locate a laptop computer that is loaded with the latest version of Cat ET.

2. Connect the computer to the communication port using the appropriate model of communication adapter.

3. Without starting the engine, turn the key switch of the machine to the ON position.

4. Note the number of diagnostic codes related to CID 1472 FMI 02.

Note: It is possible that the diagnostic code is recorded for both ECM modules.

Expected Result:

The diagnostic code is only present for "Transmission/Chassis ECM (MID 027)".

Results:

• OK - The diagnostic code is only present for "Transmission/Chassis ECM (MID 027)". Proceed to Test Step 4.

• NOT OK - The diagnostic code is present for both the "Transmission/Chassis ECM" and the "Implement ECM 2". Proceed to Test Step 2.

Test Step 2. CHECK THE POWER SUPPLY CIRCUIT OF THE SENSOR

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

2. At the J1 harness connector for the left joystick, insert 7X-1710 Multimeter Probes along the contact for the power supply J1-1 (wire R800-OR(Orange)) and along ground 1 contact J1-8 (wire P967-PU(Purple)). Do not disconnect the machine harness from the J1 connector.

3. Measure the DC voltage.

4. At the harness connectors for the left joystick, remove the multimeter probe that is inserted along the ground 1 contact J1-8 and insert the probe along ground 2 contact J1-4 (wire X800-OR(Orange)). The other probe remains inserted along the contact for the power supply J1-1 (wire R800-OR(Orange)).

5. Measure the DC voltage.

Expected Result:

Both of the voltage measurements are approximately 8.0 ± 0.4 VDC.

Results:

• OK - Both of the voltage measurements are approximately 8.0 ± 0.4 VDC. The power and ground circuits for the sensor are correct. Proceed to Test Step 3.

• NOT OK - Both of the voltage measurements are less than 8.0 ± 0.4 VDC. The power supply for the sensor is not correct.

  Repair: If both of the voltage measurements are not correct, the problem is most likely in the wire of the power circuit. This condition will cause multiple diagnostic codes to activate.

  Refer to the complete Electrical System Schematic for the machine. Examine all of the connectors that are in the power and ground circuits. Ensure that the connections are clean, that the connectors are secure and that the connectors are in good condition.

  For troubleshooting the ECM power supply, refer to the CID 0041 diagnostic code procedures in the troubleshooting section of the manual for the Implement ECM 2.

  STOP

• NOT OK - One of the voltage measurements is not correct.

  Repair: If one of the voltage measurements is correct and the other voltage measurement is not correct, there is a problem in the ground circuit that registered the bad measurement. This condition will not cause this diagnostic code to activate. There is another problem that is causing this active diagnostic code. However, the ground circuit must be repaired before proceeding with this procedure.

  Do not operate the machine with only one ground connection for the left joystick.

  Repair the faulty ground circuit or the supply circuit for the power before proceeding with this procedure.

  After repairing the faulty ground circuit, proceed to Test Step 3.

Test Step 3. CHECK THE SIGNAL AT THE SENSOR

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

1. At the machine harness connector J1 for the left joystick, use a 151-6320 Removal Tool to remove the signal wire U740-BU(Blue) and the socket at contact J1-7 from the harness connector. The machine harness connector J1 remains connected to the connector for the left joystick.

2. At the back of the connector for the joystick J1, insert 7X-1710 Multimeter Probes along the sensor signal contact J1-7 and the ground contact at J1-4.

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

4. Measure the duty cycle of the sensor at the connector contacts for the joystick J1-7 and J1-4. Move the joystick through the full range of the sensor that is described at the beginning of this procedure.

Expected Result:

The duty cycle of the "Steering Sensor 2" is correct according to the description at the beginning of this procedure.

Results:

• OK - The duty cycle of the sensor is correct. The sensor is not the cause of the problem. Reinstall the signal wire U740-BU(Blue) and the socket back to the original location at contact J1-7 in the machine harness connector for the joystick. Verify that all of the wires of the joystick are in the correct locations and that the wires are secure in the connector before proceeding to the next step. Proceed to Test Step 4.

• NOT OK - The duty cycle of the "Steering Sensor 2" is not correct according to the description at the beginning of this procedure. The sensor has failed.

  Repair: Perform this test step again in order to verify that the sensor signal is not correct.

  If the signal of the "Steering Sensor 2" is not correct according to the description at the beginning of this procedure, replace the assembly of the left joystick. After replacement of the assembly of the joystick, verify that the operation of the new assembly of the joystick is correct before operating the machine.

  STOP

Test Step 4. CHECK THE SIGNAL AT BOTH OF THE ECM MODULES

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

2. At the machine harness connector J1 for the "Transmission/Chassis ECM", insert a multimeter probe along return contact J1-45 (wire X800-OR(Orange)). At the machine harness connector J2 for the "Transmission/Chassis ECM", insert a multimeter probe along signal contact J2-48 (wire U740-BU(Blue)). The machine harness connectors remain connected to the ECM.

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

4. Measure the duty cycle of the sensor at the contacts of the ECM connector J1-45 and J2-48. Move the joystick through the full range of the sensor that is described at the beginning of this procedure.

5. At the machine harness connector J1 for the Implement ECM 2, insert a multimeter probe along return contact J1-45 (wire P967-PU(Purple)). At the machine harness connector J2 for the Implement ECM 2, insert a multimeter probe along signal contact J2-48 (wire U740-BU(Blue)). The machine harness connectors remain connected to the ECM.

6. Measure the duty cycle of the sensor at the contacts of the ECM connector J1-45 and J2-48. Move the joystick through the full range of the sensor that is described at the beginning of this procedure.

Expected Result:

The duty cycle of the "Steering Sensor 2" is correct according to the description at the beginning of this procedure at both of the ECM modules.

Results:

• OK - The duty cycle of the sensor is correct at both of the ECM modules. The machine harness does not appear to be the cause of the problem. An intermittent open or a short could still be the cause of the problem. Proceed to Test Step 5.

• NOT OK - The duty cycle of the "Steering Sensor 2" is NOT correct at one of the ECM modules according to the description at the beginning of this procedure. There is a problem in the machine harness.

  Repair: If the sensor signal at one ECM is correct and the sensor signal at the other ECM is not correct, a poor connection in the circuit would be suspected.

  The signal of the "Steering Sensor 2" at one of the ECM modules is not correct.

  Refer to the complete Electrical System Schematic of the machine. Examine all of the connectors that are in the section of the sensor signal circuit that connects to the ECM that is not receiving a good signal. Verify that the connections are clean, that all connections are secure and that all connections are in good condition. Repair the machine harness or replace the machine harness.

  STOP

• NOT OK - The duty cycle of the "Steering Sensor 2" is NOT correct at either of the ECM modules according to the description at the beginning of this procedure. It is likely that there is a problem in the machine harness. Proceed to Test Step 5.

Test Step 5. CHECK THE SIGNAL CIRCUIT FOR A SHORT

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

1. Disconnect the J1 connector and the J2 connector from the Implement ECM 2.

2. At the J2 machine harness connector for the Implement ECM 2, measure the resistance from the sensor signal contact J2-48 (wire U740-BU(Blue)) to all of the other J1 and J2 contacts that are used for the Implement ECM 2.

3. Disconnect the J1 connector and the J2 connector from the "Transmission/Chassis ECM".

4. At the J2 machine harness connector for the "Transmission/Chassis ECM", measure the resistance from the sensor signal contact J2-48 (wire U740-BU(Blue)) to all of the other J1 and J2 contacts that are used for the "Transmission/Chassis ECM".

Expected Result:

Each resistance measurement is greater than 5000 ohms.

Results:

• OK - Each resistance measurement is greater than 5000 ohms. The resistance checks of the signal circuit do not indicate a short in the machine harness. Proceed to Test Step 6.

• NOT OK - A resistance measurement is 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.

  Refer to the complete Electrical System Schematic of the machine. Check all of the connectors that are in the sensor circuit. Ensure that all connections are clean, that all connections are secure and that all connections are in good condition.

  For information on testing for short circuits and finding short circuits, refer to Testing and Adjusting, "Wiring Harness (Short Circuit) - Test". Repair the machine harness or replace the machine harness.

  STOP

Test Step 6. CHECK THE STATUS OF THE DIAGNOSTIC CODE

1. Inspect the harness connectors. Clean the contacts of the harness connectors. Check the wires for damage to the insulation that is caused by excessive heat, battery acid, or chafing.

2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the sensor circuit.

3. Reconnect all harness connectors. Make sure that the connectors are fully seated. Observe that the clips for each connector are fastened securely.

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

5. Operate the machine.

6. Determine if the CID 1472 FMI 02 diagnostic code is active.

Expected Result:

The CID 1472 FMI 02 diagnostic code is not active.

Results:

• OK - The CID 1472 FMI 02 diagnostic code is not active. The diagnostic code does not exist at this time. The initial diagnostic code was probably caused by a poor connection or a short at one of the connectors that was disconnected and reconnected. Resume normal operation.

  STOP

• NOT OK - The CID 1472 FMI 02 diagnostic code is active. The diagnostic code has not been corrected.

  Repair: Check the circuit again. Use the Cat "Electronic Technician (ET)" service tool to monitor the wiring harness of the machine. Wiggling the harness while the harness is connected to the service tool will test for intermittent connections or open connections.

  If the cause of the active diagnostic code is not found, an ECM that has activated this diagnostic code may have failed.

  If both the "Transmission/Chassis ECM" and the Implement ECM 2 have activated this diagnostic code, either ECM is probably not the cause the problem.

  Exit this procedure and perform this procedure again. If the cause of the failure is not found, contact the Technical Communicator at your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time.

  If the ECM must be replaced, refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP