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


Engine Pressure Sensor Open or Short Circuit - Test
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System Operation Description:

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

  • Boost pressure sensor

  • Atmospheric pressure sensor

  • Fuel pressure sensor

  • Engine oil pressure sensor

  • Auxiliary pressure sensor

This procedure covers the following diagnostic codes:

  • 094-03 Fuel Pressure open/short to +batt

  • 094-04 Fuel Pressure short to ground

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

  • 100-04 Engine Oil Pressure short to ground

  • 273-03 Turbo Outlet Pressure Sensor short to +batt

  • 273-04 Turbo Outlet Pressure Sensor short to ground

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

  • 274-04 Atmospheric Pressure short to ground

  • 1835-03 Auxiliary Pressure Sensor short to +batt

  • 1835-04 Auxiliary Pressure Sensor short to ground

The troubleshooting procedures for the diagnostic codes of each pressure sensor are identical. The Engine Control Module (ECM) sends a 5 volt supply to terminal A of each sensor. The sensor common connection is connected to terminal B of each sensor. The signal voltage from terminal C of each sensor is sent to the appropriate ECM connector.

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 an open in the signal circuit. When the ECM detects the presence of a voltage that is above a threshold on the signal wire, the ECM will generate a -03 diagnostic code.

If the sensor is disconnected at the sensor connector, the presence of pull-up voltage at the sensor connector indicates that the signal wire and the return wire from the sensor connector to the ECM are good.

If the sensor is disconnected at the sensor connector, the absence of pull-up voltage at the sensor connector indicates an open in the signal wire, an open in the return wire, or a short to ground.

If the sensor is disconnected at the sensor connector and the voltage on the signal wire at the sensor connector is different from pull-up voltage, the signal wire is shorted to another wire in the harness.




Illustration 1g01128578

Schematic for the engine pressure sensors

Test Step 1. Inspect the Electrical Connectors and Wiring

  1. Turn the keyswitch to the OFF position.



    Illustration 2g01129226

    Left side view

    (1) Boost pressure sensor

    (2) Atmospheric pressure sensor

    (3) Fuel pressure sensor

    (4) Engine oil pressure sensor

    (5) J2/P2 ECM connector

    (6) J1/P1 ECM connector

  1. Thoroughly inspect connectors (5) and (6). Thoroughly inspect the connectors for each engine pressure sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect".



    Illustration 3g01129248

    P2 terminals that are associated with the engine pressure sensors

    (P2-2) +5 VDC

    (P2-3) Sensor return

    (P2-14) Atmospheric pressure

    (P2-16) Fuel pressure

    (P2-24) Engine oil pressure

    (P2-40) Boost pressure




    Illustration 4g01129817

    P1 terminals that are associated with the engine pressure sensors

    (P1-2) +5 VDC

    (P1-3) Sensor return

    (P1-15) Auxiliary pressure




    Illustration 5g01123211

    Connectors for the sensors

    (A) Supply

    (B) Return

    (C) Signal




    Illustration 6g01120120

    J61 and P61 terminals that are associated with the engine pressure sensors

    (14) +5 VDC

    (15) Return

    (33) Auxiliary pressure

  1. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the engine pressure sensors.

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

  1. Check the harness and wiring for abrasions and for pinch points from each sensor 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 2.

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

    Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled. Refer to Troubleshooting, "Electrical Connectors - Inspect". Verify that the problem is resolved.

    STOP

Test Step 2. Check the Voltage on the +5 V Supply Wire

  1. Turn the keyswitch to the OFF position.

  1. Disconnect the harness connectors for the following sensors:

    • Boost pressure sensor

    • Atmospheric pressure sensor

    • Fuel pressure sensor

    • Engine oil pressure sensor

    • Auxiliary pressure sensor

  1. Turn the keyswitch to the ON position.

  1. Measure the voltage between terminals A (+5 VDC) and B (Return) at each sensor connector on the engine harness.

  1. Turn the keyswitch to the OFF position.

  1. 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. 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 the AVSpare Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

  1. Turn the keyswitch to the ON position.

  1. Observe the "Active Diagnostic" screen on Cat ET. Wait at least 15 seconds so that any codes may become active. Look for an active diagnostic code for an engine pressure sensor.

  1. 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 for the engine pressure sensors.

    Repair: If any of the above codes are logged and the engine is not running properly, refer to Troubleshooting, "Troubleshooting Without a Diagnostic Code".If the engine is running properly at this time, there may be an intermittent problem in a harness that is causing the codes to be logged. Refer to Troubleshooting, "Electrical Connectors - Inspect".

    STOP

  • Active -04 code - An 04 diagnostic code is active. Proceed to Test Step 4.

  • Active -03 code - An 03 diagnostic code is active. Proceed to Test Step 5.

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

  1. Turn the keyswitch to the OFF position.

  1. Disconnect the harness connector for the sensor with the -04 diagnostic code.

  1. Turn the keyswitch to the ON position. Wait at least 15 seconds for activation of the diagnostic codes.

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

  1. Turn the keyswitch to the OFF position.

Expected Result:

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

Results:

  • OK - A -04 diagnostic code was active before you disconnected the sensor. A -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 was active before you disconnected the sensor. The -04 diagnostic code remained after the sensor was disconnected. Leave the sensor disconnected. Proceed to Test Step 8.

Test Step 5. Check the Pull-up Voltage at the Sensor Connector

  1. Turn the keyswitch to the ON position.

  1. Disconnect the suspect sensor.

  1. Measure the voltage between terminals C (signal) and B (sensor return) at the harness connector for the sensor.

  1. Turn the keyswitch to the OFF position.

Expected Result:

The voltage is 5 ± 2 VDC.

Results:

  • OK - The voltage is 5 ± 2 VDC. The signal wire to the ECM from the sensor connector is OK.

    Repair: The open circuit is in the sensor or in the wire between the sensor and the sensor connector. Temporarily connect a new sensor to the engine harness. Do not install the sensor in the engine. Verify that no diagnostic codes are active for the new sensor before you permanently install the sensor.

    STOP

  • Not OK - The voltage is not 5 ± 2 VDC. There may be a short circuit to the signal wire in the harness. Proceed to Test Step 6.

Test Step 6. Check the Signal Wire for a Short Circuit

  1. Turn the keyswitch to the OFF position.

  1. Disconnect the J1/P1 and J2/P2 ECM connectors.

  1. Disconnect the harness connector for the suspect sensor.

  1. 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 both ECM connectors.

  1. Measure the resistance between the appropriate terminal and the engine ground.

  1. Connect J1/P1 and 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 7.

  • Not OK - At least one resistance measurement does not indicate an open circuit. There is a short circuit in the wiring for the sensor. There may be a problem with a connector.

    Repair: Repair the wiring and/or the connector. Replace parts, if necessary.Verify that the problem is resolved.

    STOP

Test Step 7. Create a Short at the Suspect Sensor Connector

  1. Turn the keyswitch to the OFF position.

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

  1. Turn the keyswitch to the ON position.

    Note: Monitor the "Active Diagnostic Codes" screen on the electronic service tool before installing the jumper wire and after installing the jumper wire.

  1. Observe the "Active Diagnostic Codes" screen on Cat ET. Wait at least 15 seconds so that any codes may become active. Look for a -04 diagnostic code.

  1. Remove the jumper wire.

  1. Turn the keyswitch to the OFF position.

Expected Result:

A -04 diagnostic code was active when the jumper wire was installed. A -03 diagnostic code became active when the jumper wire was removed.

Results:

  • OK - A -04 diagnostic code was active when the jumper wire was installed. A -03 diagnostic code became active when the jumper wire was removed. 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 - A -04 diagnostic code was active when the jumper wire was installed. The -04 code remained when the jumper wire was removed. Proceed to Test Step 8.

Test Step 8. Check the Operation of the ECM

  1. Turn the keyswitch to the OFF position.

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

    1. Disconnect the appropriate ECM connector.

    1. Remove the signal wire for the suspect sensor from the ECM connector.

    1. Remove the return wire for the suspect sensor from the ECM connector.

      Note: Disconnecting the return wire from the ECM will generate an open circuit diagnostic code for all sensors that are connected to the return wire. Ignore the additional codes. Troubleshoot the original diagnostic code and clear the codes when you are finished.

    1. Connect the ECM connector.

  1. Turn the keyswitch to the ON position.

  1. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 15 seconds so that any codes may become active.

    A -03 diagnostic code should be active for the suspect sensor.

  1. Turn the keyswitch to the OFF position.

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

    1. Disconnect the appropriate ECM connector.

    1. Install a jumper wire between the two terminals for the sensor's signal wire and the sensor's return wire.

    1. Connect the ECM connector.

  1. Turn the keyswitch to the ON position.

  1. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 15 seconds so that any codes may become active.

    A short circuit diagnostic code (04) should be active when the wire jumper is installed.

  1. Turn the keyswitch to the OFF position.

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

Expected Result:

A -03 diagnostic code was active when the signal wire was removed from the ECM connector. A -04 diagnostic code became active when the signal wire was connected to the return wire.

Results:

  • OK - The ECM is operating properly. There is a problem 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. The problem may be in a connector. Repair the return wire and/or the connector. Replace parts, if necessary.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 and/or the connector. Replace parts, if necessary.Verify that the problem is resolved.

    STOP

  • Not OK - One of the following conditions exists: The -03 diagnostic code is not active when the 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

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