797 and 797B Off-Highway Truck Caterpillar

Illustration 1	g00570214
(1) Hoist lever position sensor.

The hoist lever position sensor is located in the cab on the left side of the seat for the operator.

Illustration 2	g02270594
Schematic Of The Hoist Lever Position Sensor

This diagnostic code is recorded when the Chassis ECM reads the voltage of the hoist lever position sensor as being below normal. The voltage of the signal wire (M996-PK) is below normal and/or shorted to ground. The hoist lever position sensor is a component that produces a PWM output. The sensor signal wire (M996-PK) connects to connector J1-51 of the ECM connector.

The possible causes of this diagnostic code are listed:

• A shorted harness

• The sensor has failed.

• The ECM may have failed. A failure of the Chassis ECM is unlikely.

System Response:

The status of the hoist lever is unknown. The hoist system will remain in the HOLD position. The hoist system will not be able to raise the body. The hoist system will not be able to dump the body. After the diagnostic code has been corrected, the hoist lever must be returned to the HOLD position before returning to normal operation.

Test Step 1. CHECK THE SENSOR.

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

2. Ensure that the diagnostic code is present.

3. Observe the status of the diagnostic code. Then, disconnect the machine harness from the sensor.

Expected Result:

If the sensor is not the cause of the diagnostic code, the diagnostic code remains present. If the sensor has failed, the diagnostic code is NO longer present.

Results:

• OK - The diagnostic code is present. The sensor has NOT failed. The machine harness or the ECM may have failed. Proceed to Test Step 2.

• NOT OK - The diagnostic code is NOT present. The machine harness is correct and the ECM is operating properly.

  Repair: The sensor has failed. Replace the sensor.

  STOP

Test Step 2. CHECK THE SIGNAL CIRCUIT FOR A SHORT TO GROUND.

1. The sensor remains disconnected from the machine harness.

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

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

4. Measure the resistance from J1-51 wire (M996-PK) to all possible sources of ground. The possible sources of ground are listed: J1-9, J1-12, J2-2, J2-12, J2-13, J2-18, J2-22, J2-36, J2-46, J2-49, J2-52, J2-56, J2-59, J2-69 and frame ground.

Expected Result:

The resistance should be greater than 5000 ohms.

Results:

• OK - The resistance that is measured is greater than 5000 ohms for each measurement. Proceed to Test Step 3.

• NOT OK - The resistance that is measured is less than 5 ohms for one or more of the measurements. There is a short in the harness.

  Repair: The short is between the signal circuit (M996-PK) and a ground source. Repair the machine harness or replace the machine harness.

  STOP

Test Step 3. CHECK IF THE DIAGNOSTIC CODE REMAINS.

1. Clean the contacts of the harness connectors.

2. Reconnect all harness connectors.

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

4. Observe the status of the diagnostic code.

5. Operate the machine.

6. Observe the status of the diagnostic code.

Expected Result:

The CID 0773 FMI 04 diagnostic code is present.

Results:

• OK - The CID 0773 FMI 04 diagnostic code is present. The diagnostic code has not been corrected. The ECM may have failed.

  Repair: A failure of the Chassis ECM is unlikely. If the cause of the diagnostic code is not found, then replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP

• NOT OK - The diagnostic code is NOT present. The diagnostic code does not exist at this time.

  Repair: The initial diagnostic code was probably caused by a poor electrical connection or a short at one of the harness connectors. Resume normal machine operation.

  STOP