3176C Engines for Caterpillar Built Machines Caterpillar

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

• Engine oil pressure sensor

• Turbocharger outlet pressure sensor

• Atmospheric pressure sensor

• Turbocharger inlet pressure sensor

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

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

• 100-04 Engine Oil Pressure short to ground

• 273-03 Turbo Outlet Pressure open/short to +batt

• 273-04 Turbo Outlet Pressure short to ground

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

• 274-04 Atmospheric Pressure short to ground

• 275-03 Right Turbo Inlet Pressure open/short to +batt

• 275-04 Right Turbo Inlet Pressure short to ground

The 5 volt sensor supply provides power to all 5 volt sensors. The Electronic Control Module (ECM) supplies 5.0 ± 0.2 VDC to terminal A of each sensor connector. The sensor return 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.

Pull-up Voltage

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	g01276328
Schematic for the engine pressure sensors

Illustration 2	g01284827
(1) Turbocharger outlet pressure sensor (2) Atmospheric pressure sensor (3) Engine oil pressure sensor (4) J2/P2 ECM connector (5) J1/P1 ECM connector

Illustration 3	g01284819
Air cleaner assembly (typical example) (6) Turbocharger inlet pressure sensor

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove electrical power from the ECM.

2. Thoroughly inspect connectors (2) and (3). Also, thoroughly inspect the connectors for each pressure sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect".

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Illustration 4	g01284855
P2terminal locations (P2-2) +5 V Sensor supply (P2-3) Sensor return (P2-14) Atmospheric pressure sensor (P2-24) Engine oil pressure sensor (P2-40) Turbocharger outlet pressure sensor

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Illustration 5	g01284860
P1 terminal locations (P1-2) +5 V Sensor supply (P1-3) Sensor return (P1-15) Turbocharger inlet pressure sensor

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Illustration 6	g01159881
Sensor connector (Terminal A) +5 V sensor supply (Terminal B) Sensor return (Terminal C) Signal

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connectors and on each of the wires in the pressure sensor connectors.

4. Check the allen head screw for each ECM connector and the customer connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

5. Check the harness and wiring for abrasion and for pinch points from the pressure 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 appear to be OK. Proceed to Test Step 2.

• 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 electrical power from the ECM.

2. Disconnect the harness connectors for the following sensors:
   • Engine oil pressure sensor

   • Turbocharger outlet pressure sensor

   • Atmospheric pressure sensor

   • Turbocharger inlet pressure sensor

3. Restore electrical power to the ECM.

   Note: The original diagnostic code may not stay active. 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.

Note: Be sure to wiggle the harness during the following measurements in order to reveal an intermittent condition.

4. Measure the voltage between terminals A and B at each sensor connector on the engine harness.

5. Remove electrical power from the ECM.

6. Connect all of the sensors.

Expected Result:

Each voltage measurement is 5.0 ± 0.2 VDC.

Results:

• OK - Each voltage measurement is 5.0 ± 0.2 VDC. The voltage is correct at the sensor connectors. Proceed to Test Step 3.

• Not OK - At least one voltage measurement is not 5.0 ± 0.2 VDC.

  Repair: Refer to 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 electrical power to the ECM.

3. Monitor the active diagnostic code screen on Cat ET. Look for an active diagnostic code for an engine pressure sensor.

   Note: Wait at least 30 seconds so that any codes may become active.

4. Determine if the problem is related to an open circuit diagnostic code (03) or a short circuit diagnostic code (04).

Expected Result:

No diagnostic codes are active.

Results:

• OK - No diagnostic codes are active for the engine pressure sensors.

  Repair: The original problem seems to be resolved. The problem may have been related to a faulty connection in the harness. Carefully reinspect the connectors and wiring. If an intermittent electrical problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - A 03 diagnostic code is active at this time. The ECM is detecting an open circuit condition. Proceed to Test Step 5.

• Not OK - A 04 diagnostic code is active at this time. The ECM is detecting a short circuit condition. Proceed to Test Step 4.

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

1. Remove electrical power from the ECM.

2. Disconnect the sensor connector of the sensor with the short circuit diagnostic code (04).

3. Restore electrical power to the ECM.

4. Access the "Active Diagnostic Code" screen on Cat ET. Check for an active open circuit diagnostic code (03) while the sensor is disconnected.

   Note: Wait at least 30 seconds for activation of the diagnostic codes.

5. Remove electrical power from the ECM.

Expected Result:

A 03 diagnostic code became active after the sensor was disconnected.

Results:

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

  Repair: There may be a problem with a sensor. 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 - When the sensor is disconnected, a 04 diagnostic code remains active for the suspect sensor. There is a problem in the circuit between the sensor harness connector and the ECM. The problem may be in the ECM. Leave the sensor disconnected. Proceed to Test Step 6.

Test Step 5. Create a Short at the Suspect Sensor Connector

1. Remove electrical power from the ECM.

2. Fabricate a jumper wire that is long enough to short the terminals at the sensor connector. Crimp connector sockets to each end of the jumper wire.

3. Install the jumper wire between terminal B (sensor return) and terminal C (sensor signal) on the harness side of the suspect sensor's connector.

4. Restore electrical power to the ECM.

5. Monitor the "Active Diagnostic Codes" screen on Cat ET. Check for an active short circuit diagnostic code (04) while the jumper wire is installed.

   Note: Wait at least 30 seconds for activation of the diagnostic code.

6. Remove electrical power from the ECM.

7. Remove the jumper wire.

Expected Result:

A 04 diagnostic code was active when the jumper wire was installed.

Results:

• OK - A 04 diagnostic code was active when the jumper wire was installed.

  Repair: There is a problem with the sensor. 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. There is a problem in the harness between the ECM and the sensor connector. There may be a problem with the ECM. Proceed to Test Step 6.

Test Step 6. Test the Operation of the ECM

1. Remove electrical power from the ECM.

2. Fabricate a jumper wire that is long enough to create a test circuit from the ECM connector to the engine ground stud. Crimp a connector socket to one end of the jumper wire.

3. Disconnect the appropriate ECM connector.

4. Remove the suspect sensor's signal wire from the ECM connector. Install the jumper wire into this terminal location at the ECM connector.

5. Connect the ECM connectors.

6. Check the operation of the ECM by creating an open at the ECM:

   1. Hold the loose end of the jumper wire away from any ground source in order to create an open circuit condition.

   2. Restore electrical power to the ECM.

   3. Monitor the "Active Diagnostic Code" screen on Cat ET. Check the suspect sensor for an active 03 diagnostic code.

      Note: Wait at least 30 seconds so that any codes may become active.

   4. Remove electrical power from the ECM.

7. Check the operation of the ECM by creating a short circuit at the ECM:

   1. Connect the jumper wire to the engine ground stud.

   2. Restore electrical power to the ECM.

   3. Monitor the "Active Diagnostic Code" screen on Cat ET. Check the suspect sensor for an active 04 diagnostic code while the jumper wire is installed.

      Note: Wait at least 30 seconds so that any codes may become active.

   4. Remove electrical power from the ECM.

8. Remove the jumper wire. Return the wiring to the original configuration.

Expected Result:

A 03 diagnostic code is active when the loose end of the jumper wire is open. A 04 diagnostic code is active when the loose end of the jumper wire is connected to the engine ground stud.

Results:

• OK - A 03 diagnostic code is active when the loose end of the jumper wire is open. A 04 diagnostic code is active when the loose end of the jumper wire is connected to the engine ground stud.

  Repair: The ECM is operating properly. The problem is in the harness wiring between the ECM and the sensor connector.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.

  STOP

• Not OK - One of the following conditions exists: The 03 diagnostic code is not active when the loose end of the jumper wire is open. The 04 diagnostic code is not active when the loose end of the jumper wire is grounded.

  Repair: There is a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "Replacing the ECM".

  STOP