3126B Machine Engines Engine Pressure Sensor Open or Short Circuit - Test Caterpillar

System Operation Description:

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

• Fuel pressure sensor

• Engine oil pressure sensor

• Injection actuation pressure sensor

• 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

• 164-03 Injector Actuation Pressure voltage high

• 164-04 Injector Actuation Pressure voltage low

• 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

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	g01330734
Schematic for the engine pressure sensors

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Turn the keyswitch to the OFF position.
   Show/hide table

   Illustration 2	g01330735
   Left side engine view (typical example) (1) Injection actuation pressure sensor (2) Boost pressure sensor (3) Atmospheric pressure sensor (4) Fuel pressure sensor (5) Engine oil pressure sensor (6) J2/P2 ECM connector

2. Thoroughly inspect the connectors for pressure sensors (1), (2), (3), (4), and (5). Also, thoroughly inspect connector (6). Refer to Troubleshooting, "Electrical Connectors - Inspect".
   Show/hide table

   Illustration 3	g01330756
   P2 terminal locations for the engine pressure sensors (P2-2) +5 V sensor supply (P2-3) Sensor return (P2-14) Atmospheric pressure (P2-16) Fuel pressure (P2-24) Engine oil pressure (P2-27) Injection actuation pressure (P2-40) Boost pressure (P2-41) +5 V sensor supply (P2-42) Sensor return

   Show/hide table

   Illustration 4	g01159881
   Sensor connector (A) +5 V supply (B) Sensor return (C) Signal

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connectors that are associated with the circuit.

4. Check the allen head screw for each ECM 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 and the harness and wiring are free of corrosion, of abrasion and of pinch points.

Results:

• OK - The harness and connectors appear to be OK. Proceed to Test Step 2.

• Not OK - There is a problem with 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. Turn the keyswitch to the OFF position.

2. Disconnect the harness connectors for the following sensors:

   • Atmospheric pressure sensor

   • Boost pressure sensor

   • Engine oil pressure sensor

   • Fuel pressure sensor

   • Injection actuation pressure sensor

3. Turn the keyswitch to the ON position.

   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. Turn the keyswitch to the OFF position.

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 AVSpare Electronic Technician (ET) to the service tool connector.

2. Turn the keyswitch to the ON position.

3. Observe the "Active Diagnostic" screen on Cat ET. Wait at least 45 seconds so that any codes may become active. Look for an active diagnostic code for an engine pressure sensor.

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

Expected Result:

No diagnostic codes are active.

Results:

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

  Repair: The problem may have been related to a faulty connection in the harness. Carefully reinspect the connectors and wiring. Refer to 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 and Check for an Open Circuit

1. Turn the keyswitch to the OFF position.

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

3. Turn the keyswitch to the ON position. Wait at least 45 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. Turn the keyswitch to the OFF position.

Expected Result:

An -03 diagnostic code is now active for the disconnected sensor.

Results:

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

  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. Turn the keyswitch to the OFF position.

2. Disconnect the J2/P2 ECM connectors.

3. Disconnect the harness connector for the suspect sensor.

4. Identify the terminal for the signal wire on the ECM connector that is appropriate for the suspect sensor. Measure the resistance between the appropriate terminal and the remaining terminals on the ECM connector.

5. Connect the J2/P2 ECM connectors. Connect the connectors for the suspect sensor.

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: There is a short circuit in the wiring for the sensor. There may be a problem with a connector. Repair the wiring and/or the connector. Replace parts, if necessary. Verify that the problem is resolved.

  STOP

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

1. Turn the keyswitch to the OFF position.

2. Install a jumper wire with socket terminals on each end between terminals B (sensor return) and C (signal) on the harness connector for the suspect sensor.

3. Turn the keyswitch to the ON position.

4. Wait at least 45 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. Turn the keyswitch to the OFF position.

Expected Result:

An -04 diagnostic code was active when the jumper wire was installed. An -03 diagnostic code became active when the jumper wire was 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 new sensor, permanently install the new sensor. Clear any logged diagnostic codes. Verify that the problem is resolved.

  STOP

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

Test Step 7. Check the Operation of the ECM

1. Turn the keyswitch to the OFF position.

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

   1. Disconnect the J2/P2 ECM connector.

   2. Remove the signal wire for the suspect sensor from the ECM connector. Install a jumper wire into the terminal location for the suspect sensor at the ECM connector.

   3. Connect the ECM connector.

   4. Hold the loose end of the jumper wire away from any components in order to create an open circuit condition.

   5. Turn the keyswitch to the ON position.

   6. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 45 seconds so that any codes may become active.

      Check the suspect sensor for an active -03 diagnostic code.

   7. Turn the keyswitch to the OFF position.

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

   1. Short the jumper wire for the suspect sensor to engine ground in order to create a short circuit condition.

4. Turn the keyswitch to the ON position.

5. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 45 seconds so that any codes may become active.

   Check the suspect sensor for an active -04 diagnostic code while the jumper wire is installed.

6. Turn the keyswitch to the OFF position.

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

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 engine ground stud.

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