C18 Engines for Caterpillar Built Machines Caterpillar

Use this procedure to troubleshoot any suspect problems with the following sensors:

• Fuel pressure sensor

• Engine oil pressure sensor

• Intake manifold (boost) pressure sensor

• Atmospheric pressure sensor

This procedure covers the following open circuit diagnostic codes and short circuit diagnostic codes:

• 94-03 Fuel Pressure open/short to +batt

• 94-04 Fuel Pressure short to ground

• 100-03 Engine Oil Pressure open/short to +batt

• 100-04 Engine Oil Pressure short to ground

• 102-03 Boost Pressure Sensor open/short to +batt

• 102-04 Boost Pressure Sensor short to ground

• 274-03 Atmospheric Pressure open/short to +batt

• 274-04 Atmospheric Pressure short to ground

The 5 volt sensor supply provides power to all 5 volt sensors. The Electronic Control Module (ECM) supplies 5.0 ± 0.16 VDC to terminal A of each sensor connector. The sensor common from the ECM connector goes to terminal B of each sensor connector. The sensor supply is output short circuit protected. A short circuit to the battery will not damage the circuit inside the ECM.

Note: The sensors are not protected from overvoltage. A short from the supply line to the +Battery may damage the sensors. If the CID-FMI 262-03 is logged, it is possible that all of the sensors have been damaged. Repair the sensor supply and check for any "ACTIVE" sensor diagnostic codes in order to determine if a sensor has failed.

Pull-up Voltage

Note: The pull-up voltage may vary between applications.

The ECM continuously outputs a pull-up voltage on the circuit for the sensor signal wire. The ECM uses this pull-up voltage in order to detect a problem in the signal circuit. When the ECM detects the presence of a voltage that is above a threshold on the signal circuit, the ECM will generate a 03 diagnostic code for the sensor.

If the sensor is disconnected at the sensor connector, the presence of pull-up voltage at the sensor connector indicates that the wires from the sensor connector to the ECM are OK. If the sensor is disconnected at the sensor connector, the absence of pull-up voltage at the sensor connector indicates a problem in the signal wire. If the sensor is disconnected at the sensor connector and the voltage at the sensor connector is different from pull-up voltage, the signal wire is shorted to another wire in the harness.

Illustration 1	g01285456
Schematic

Illustration 2	g01024457
P2 ECM connector (P2-15) Intake manifold (boost) pressure sensor (P2-17) Sensor common (P2-28) Engine oil pressure sensor (P2-40) Fuel pressure sensor (P2-57) Atmospheric pressure sensor (P2-72) +5 V Supply

Illustration 3	g01119637
Typical C18 Sensor locations (1) Intake manifold (boost) pressure sensor (2) Fuel pressure sensor (3) Atmospheric pressure sensor (4) Engine oil pressure sensor

Illustration 4	g01094844
Sensor connector

Test Step 1. Inspect Electrical Connectors and Wiring

1. Remove the electrical power from the ECM.

2. Thoroughly inspect the J1/P1 ECM connector and the J2/P2 ECM connector. Thoroughly inspect the connectors for each analog sensor.

   Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the sensor connectors that are associated with the active diagnostic code.

4. Check the ECM connector (allen head screw) for the proper torque. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect" for details.

5. Check the harness and wiring for abrasions and for pinch points from the sensors back to the ECM.

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.

Results:

• OK - The harness and wiring are OK. Proceed to Test Step 5.

• Not OK - There is a problem in the connectors and/or wiring.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check the Supply Voltage at the Sensor Connector

1. Remove the electrical power from the ECM.

2. Disconnect all of the following analog sensors at the sensor connector:
   • Fuel pressure sensor

   • Engine oil pressure sensor

   • Intake manifold (boost) pressure sensor

   • Atmospheric pressure sensor

3. Restore the electrical power to the ECM.

   Note: The original diagnostic code may go away. An open circuit diagnostic code for the sensor supply may become active when all of the sensors are disconnected. Ignore the active codes at this time and continue with this test step.

4. Measure the voltage between terminal A (5 V analog supply) and terminal B (sensor return) at the sensor connectors.

5. Remove the electrical power from the ECM.

6. Reconnect all sensors.

Expected Result:

The voltage is 5.0 ± 0.16 VDC.

Results:

• OK - The voltage is 5.0 ± 0.16 VDC. The voltage is correct. Proceed to Test Step 3.

• Not OK - The voltage is not 5.0 ± 0.16 VDC. The voltage is incorrect.

  Repair: Perform the diagnostic functional test Troubleshooting, "5 Volt Engine Pressure Sensor Supply Circuit - Test".

  STOP

Test Step 3. Check for Active Diagnostic Codes

1. Connect Caterpillar Electronic Technician (ET) to the service tool connector.

2. Restore the electrical power to the ECM.

3. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

4. Determine if the problem is related to a 03 diagnostic code or a 04 diagnostic code.

Expected Result:

No diagnostic codes are active.

Results:

• OK - No diagnostic codes are active.

  Repair: The problem may have been related to a faulty connection in the harness. Carefully reinspect the connectors and wiring. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - A 04 diagnostic code is active at this time. Proceed to Test Step 4.

• Not OK - A 03 diagnostic code is active at this time. Proceed to Test Step 5.

Test Step 4. Disconnect the Suspect Sensor in Order to Create an Open Circuit

1. Remove the electrical power from the ECM.

2. Disconnect the sensor connector of the suspect sensor with the active 04 diagnostic code.

3. Restore the electrical power to the ECM. Wait at least 30 seconds for activation of the diagnostic codes.

4. Access the "Active Diagnostic Code" screen on Cat ET. Check for an active 03 diagnostic code.

5. Remove the electrical power from the ECM.

Expected Result:

A 03 diagnostic code is now active for the suspect sensor.

Results:

• OK - A 04 diagnostic code was active before disconnecting the sensor. A 03 diagnostic code became active after disconnecting the sensor.

  Repair: Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Verify that there are no active diagnostic codes for the sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes.

  STOP

• Not OK - A 04 diagnostic code is still active for the suspect sensor. There is a short circuit between the sensor harness connector and the ECM. Leave the sensor disconnected. Proceed to Test Step 7.

Test Step 5. Check the Signal Wire for a Short Circuit

1. Remove the electrical power from the ECM.

2. Disconnect ECM connectors P1 and P2.

3. Disconnect the connector for the sensor.

4. Measure the resistance between the terminal for the sensor signal wire at the ECM and every terminal on ECM connector P1 and ECM connector P2.

5. Reconnect ECM connector P1 and ECM connector P2.

Expected Result:

Each resistance measurement indicates an open circuit.

Results:

• OK - Each resistance measurement indicates an open circuit. Proceed to Test Step 6.

• Not OK - At least one resistance measurement does not indicate an open circuit.

  Repair: The resistance measurement indicates a low resistance between two or more wires. Repair the connectors or wiring and/or replace the connectors or wiring.

  STOP

Test Step 6. Create a Short at the Suspect Sensor Connector

1. Remove the electrical power from the ECM.

2. Install a jumper wire with Deutsch sockets on each end between terminal B (sensor return) and terminal C (signal) on the connector for the suspect sensor. Connect the jumper on the harness side of the connector.

3. Restore the electrical power to the ECM.

4. Wait at least 30 seconds for activation of a 04 diagnostic code.

   Note: Monitor the "Active Diagnostic Codes" screen on Cat ET before installing the jumper wire and after installing the jumper wire.

5. Remove the jumper wire.

6. Remove the electrical power from the ECM.

Expected Result:

A 04 diagnostic code is active when the jumper wire is installed. A 03 diagnostic code is active when the jumper wire is removed.

Results:

• OK - The engine harness and the ECM are OK.

  Repair: Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Verify that there are no active diagnostic codes for the sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes.

  STOP

• Not OK - The 03 diagnostic code remains active with the jumper in place. The open circuit is between the ECM and the sensor connector. Proceed to Test Step 7.

Test Step 7. Check the Operation of the ECM

1. Remove the electrical power from the ECM.

2. Check the operation of the ECM by creating an open at the ECM.

   1. Disconnect the J2/P2 ECM connector. Remove the signal wire for the suspect sensor from the ECM connector.

   2. Install a jumper wire with Deutsch sockets on each end into the socket for the signal wire of the suspect sensor.

   3. Reconnect the ECM connectors.

   4. Restore the electrical power to the ECM. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 30 seconds for activation of the code.

      An open circuit diagnostic code (03) should be active for the suspect sensor.

3. Check the operation of the ECM by creating a short at the ECM.

   1. Install a wire jumper between the wire jumper for the signal wire for the suspect sensor and engine ground.

   2. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 15 seconds for activation of the code.

      A 04 diagnostic code should be active when the wire jumper is installed.

   3. Remove the wire jumper. Reconnect all wires and connectors.

Expected Result:

A 03 diagnostic code is active when the sensor signal wire is removed from the ECM connector. A 04 diagnostic code is active when the signal wire is connected to the sensor return.

Results:

• OK - The ECM is operating properly. The problem is in the wiring between the ECM and the sensor connector.

  Repair: If the code is active for more than one sensor, the problem is most likely in the return wire for the sensor. Repair the return wire for the sensor or replace the harness.If the code is only active for one sensor, the problem is most likely in the signal wire for the sensor. Repair the signal wire for the sensor.

  STOP

• Not OK - One of the following conditions exists: The 03 diagnostic code is not active when the sensor signal wire is disconnected. The 04 diagnostic code is not active when the wire jumper is installed.

  Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM". Verify that the problem is resolved.

  STOP