789D CMD Off-Highway Truck Chassis Electronic Control System (Command For Hauling) Caterpillar

MID 087 - Chassis ECM

CID 1494 - Steering Accumulator Oil Pressure Sensor

FMI 04 - Voltage Below Normal

Illustration 1	g06351803
Steering accumulator oil pressure sensor circuit

This diagnostic code indicates the "Chassis" ECM detects "Steering Accumulator Oil" pressure sensor voltage is below normal.

The following can cause this code:

• Sensor signal circuit shorted to ground

• Sensor failure

• ECM failure

Note: The following test procedure may create other diagnostic codes. Ignore these created codes and clear these created codes after the original diagnostic code has been corrected. Ensure diagnostic code CID 1175 FMI 04 is active before performing this procedure.

The output frequency of the sensor is approximately 500 Hz. The duty cycle of the signal is proportional to the pressure that is applied. The duty cycle varies from 3% to 95%.

Note: Use a calibrated digital multimeter for this procedure.

System Response:

Since the "Steering Pressure" value is unknown, the "Chassis" ECM commands the "Steering Pump" to full displacement.

Test Step 1. CHECK THE SENSOR

1. Turn on the key switch and the disconnect switch.

2. Disconnect the sensor from the harness while observing the diagnostic code status.

Expected Result:

CID 1175 FMI 04 remains active and does not change.

Results:

• OK - CID 1175 FMI 04 remains active and does not change. Proceed to Test Step 2.

• NOT OK - CID 1175 FMI 04 remains active, FMI 04 changes. The sensor has failed.

  Repair: Replace the sensor.

  STOP

Test Step 2. CHECK HARNESS FOR A SHORT TO GROUND

The sensor remains disconnected from the harness.

1. Turn off the key switch and the disconnect switch.

2. Disconnect the harness from the "Chassis" ECM.

3. At the harness connector for the "Chassis" ECM, measure the resistance from signal contact J2-41 (wire C450-YL(Yellow)) to all possible sources of ground for the "Chassis" ECM harness connectors.

Expected Result:

Each resistance is greater than 5000 ohms.

Results:

• OK - Each resistance is greater than 5000 ohms. Proceed to Test Step 3.

• NOT OK - A resistance is less than 5000 ohms There is a short between signal contact J2-41 (wire C450-YL(Yellow)) and the circuit with low resistance.

  Repair: Repair or replace the harness.

  STOP

Test Step 3. CHECK THE DIAGNOSTIC CODE

The key switch and the disconnect switch remain in the off position.

1. Inspect the harness.

   Clean the harness connector contacts.

   Inspect the harness connector contacts for corrosion or damage.

   Inspect the wire insulation for damage caused by heat, corrosion, or chafing.

2. Perform a 45 N (10 lb) pull test on each circuit wire.

3. Reconnect all harness connectors.

   Verify that the connectors are fully seated and the clips are fastened.

4. Check for intermittent problems. Using Cat^® Electronic Technician (Cat^® ET), perform a wiggle test on the harness.

5. Turn on the disconnect switch and the key switch.

6. Operate the machine.

7. Check CID 1494 FMI 04 status.

Expected Result:

CID 1175 FMI 04 is not active.

Results:

• OK - CID 1494 FMI 04 is not active.

  Repair: The initial diagnostic code was probably caused by a poor connection at one of the connectors that was checked.

  Resume normal operation.

  STOP

• NOT OK - CID 1175 FMI 04 is active. The ECM may have failed.

  Repair: Exit this procedure and perform this procedure again. Contact your technical communicator. If the ECM requires replacement, see Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  STOP