Cat® Command For Hauling Caterpillar

MID 039 - Machine Control Module

CID 0840 - Left Rear Strut Pressure Sensor

FMI 04 - Voltage Below Normal

Illustration 1	g06042529
Mini schematic of the left rear strut pressure sensor circuit

This diagnostic code indicates the Input/Output Module (I/O Module) detects the Left Rear Strut Pressure Sensor voltage is below normal.

The output frequency of the sensor changes as the pressure in the suspension cylinder changes. The sensor is powered by the machine electrical system.

Note: This test checks for sensor voltages at the sensor when all the circuits are connected. Unless directed otherwise, do not disconnect any components. Troubleshoot the circuit "as is" before disconnecting any components.

Note: Use a calibrated digital Multimeter for this procedure.

Test Step 1. CHECK THE SENSOR SUPPLY VOLTAGE

1. Locate the suspect sensor.

2. Identify the sensor wires and connector contacts.

   Note: Do NOT disconnect any harness connectors.

3. Turn ON the keyswitch.

   Note: The truck can be empty or the truck can be loaded

4. At the sensor connector, identify the +V and ground circuits

5. Insert 7X-1710 Multimeter Probe leads beside the +V and ground circuit wires in the back of the connector for the sensor.

6. Measure the voltage.

Expected Result:

The voltage is between 22.0 DCV and 29.5 DCV.

Results:

• OK - The voltage is between 22.0 DCV and 29.5 DCV. Proceed to Test Step 1.

• NOT OK - The voltage is not between 22.0 DCV and 29.5 DCV.

  Repair: Trace the +V and ground circuits in the harness.

  Perform one of the following:

  • Repair or replace the harness if the harness has failed

  • Replace the sensor if the harness has not failed

  STOP

Test Step 2. CHECK THE SENSOR SIGNAL VOLTAGE

1. At the sensor connector, identify the signal and ground circuits.

2. Insert 7X-1710 Multimeter Probe leads beside the signal and ground circuit wires in the back of the connector for the sensor.

3. Measure the voltage

Expected Result:

The voltage is between 1.0 DCV and 9.0 DCV.

Results:

• NOT OK - The voltage is greater than 9.0 DCV. Proceed to Test Step 1.

• NOT OK - The voltage is less than 1.0 DCV. Proceed to Test Step 1.

• OK - The voltage is between 1.0 DCV and 9.0 DCV. Proceed to Test Step 1.

Test Step 3. CHECK THE SIGNAL CIRCUIT FOR A SHORT TO +BATTERY

1. Disconnect the sensor from the harness.

2. At the harness connector for the sensor, measure the voltage between the signal contact and the ground contact.

Expected Result:

The voltage is less than 9.0 DCV.

Results:

• OK - The voltage is between 1.0 and 9.0 DCV. The voltage is correct, the sensor has failed.

  Repair: Replace the sensor.

  STOP

• NOT OK - The voltage is above 9.0 DCV. The signal circuit is shorted to the +battery or the Input/Output Module (I/O Module) has failed.

  Repair: Trace the signal and ground circuits in the harness. Repair or replace the harness. If the harness is correct, the Input/Output Module (I/O Module) may have failed. Contact the Technical Communicator at your Cat^® Dealer.

  STOP

Test Step 4. CHECK THE SIGNAL CIRCUIT FOR A SHORT TO GROUND

1. Disconnect the sensor from the harness.

2. At the harness connector for the sensor, measure the voltage between the signal contact and the ground contact.

Expected Result:

The voltage is between 1.0 and 9.0 DCV.

Results:

• OK - The voltage is between 1.0 and 9.0 DCV. The voltage is correct, the sensor has failed.

  Repair: Replace the sensor.

  STOP

• NOT OK - The voltage is less than 1.0 DCV.

  Repair: Possible causes:

  • Incorrect software installed

  • Signal circuit shorted to ground in the harness

  • Input/Output Module (I/O Module) has failed
  Verify the possible causes in the following order:

  1. Check that the correct VIMS software is installed.

     Install the correct VIMS software.

  2. Trace the signal circuit and the ground circuit in the harness.

     Repair or replace the harness.

  3. If the harness is correct, the Input/Output Module (I/O Module) may have failed.

     Contact the Technical Communicator (TC) at your Cat^® Dealer.

  STOP

Test Step 5. CHECK THE SENSOR SIGNAL FREQUENCY

1. Remove the sensor from the suspension cylinder.

   Note: Do NOT disconnect the harness connector.

2. At the harness connector for the sensor, identify the signal and ground circuits.

   Note: Do NOT disconnect or reconnect the harness connector.

3. Insert 7X-1710 Multimeter Probe leads beside the signal and ground circuit wires in the back of the connector for the sensor.

4. Measure the frequency between the signal and the ground contacts.

Expected Result:

The frequency is between 186 Hz and 214 Hz when ambient temperature is between 10° C (50.0 ° F) and 40° C (104.0 ° F).

Results:

• OK - The frequency is correct. If the problem of incorrect payload measurement persists, proceed to Test Step 1.

• NOT OK - The frequency is not correct. The sensor has failed.

  Repair: Replace the sensor.

  STOP

Test Step 6. MOVE THE SENSOR

1. Substitute the suspect sensor with a properly functioning sensor.

   For example, substitute the suspect left front suspension cylinder pressure sensor with a good right front suspension cylinder pressure sensor.

2. Verify that the problem followed the suspect sensor to the other suspension cylinder.

   Verify that the problem followed the suspect sensor:

   • Ride in the truck during the loading operation

   • Observe the performance of the four suspension cylinder pressure sensors by using Cat ET or by activating a data logger

   • Compare the signal outputs of the four sensors

   • Verify that the suspect sensor does not respond to the loading of the truck in the same manner as the other sensors

Expected Result:

The problem followed the sensor to the other suspension cylinder.

Results:

• OK - The problem followed the sensor to the other suspension cylinder. The sensor has failed.

  Repair: Replace the sensor.

  STOP

• NOT OK - The problem did not follow the sensor to the other suspension cylinder. The suspension cylinder is causing the failure. Proceed to Test Step 1.

Test Step 7. CHECK THE SUSPENSION CYLINDERS

1. Verify that the following conditions are not present.

   The suspension cylinders are not sticking when the truck is empty.

   The suspension cylinders are not bottoming out when the truck is loaded.

   Verify that the above conditions are not present:

   • Ride in the truck during the loading operation

   • Observe the operation of the four suspension cylinder pressure sensors with Cat ET or activate a data logger

   • Compare the signal outputs of the four sensors

   • Verify that the sensor responds to the loading of the truck in the same manner as the other sensors

Expected Result:

The above conditions are not present.

Results:

• OK - The above conditions are not present.

  Repair: Repeat this procedure.

  STOP

• NOT OK - The above conditions are present.

  Repair: Service the suspension cylinder in accordance with the Special Instruction, SEHS9411, "Servicing the Suspension Cylinders for Off-Highway Trucks".

  STOP