3126B Engine for Caterpillar Built Machines Caterpillar

Use this procedure to troubleshoot the system only when there is an active diagnostic code or when a diagnostic code can easily be activated. This procedure covers open circuit diagnostic codes and short circuit diagnostic codes that are associated with the following sensors:

• Atmospheric pressure sensor

• Engine oil pressure sensor

• Fan drive pressure sensor

• Fuel pressure sensor

• Injection actuation pressure sensor

• Turbocharger outlet pressure sensor

Illustration 1	g00904082
Schematic

Test Step 1. Check for Active +5 V Sensor Supply Diagnostic Codes

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

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

3. Verify that neither of the following diagnostic codes are active:
   • 262-03 5 Volt Sensor Supply short to +batt

   • 262-04 5 Volt Sensor Supply short to ground

Expected Result:

Neither of the preceding diagnostic codes are active.

Results:

• OK - The diagnostic codes are not active. Proceed to Test Step 2.

• Not OK - At least one of the diagnostic codes is active.

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

  Stop.

Test Step 2. Verify all Active Diagnostic Codes

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

2. Verify if any of the following diagnostic codes are active:
   • 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 open/short to +batt

   • 164-04 Injector Actuation Pressure short to ground

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

   • 273-04 Turbocharger Outlet Pressure short to ground

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

   • 274-04 Atmospheric Pressure short to ground

   • 290-03 Engine Fan Pump Pressure open/short to +batt

   • 290-04 Engine Fan Pump Pressure short to ground

Expected Result:

One or more of the preceding diagnostic codes are active.

Note: The following diagnostic codes should not be active:

• 262-03 5 Volt Sensor Supply short to +batt

• 262-04 5 Volt Sensor Supply short to ground

Results:

• OK - Proceed to Test Step 3.

• Not OK -

  Repair: If the preceding codes are logged but not active and the engine is not running properly, refer to Troubleshooting, "Troubleshooting without a Diagnostic Code". If the engine is running properly at this time, an intermittent condition may be causing the logged codes. Refer to Troubleshooting, "Electrical Connectors - Inspect".

  Stop.

Test Step 3. Inspect Electrical Connectors and Wiring

Illustration 2	g00904083
ECM connectors (wire side)

1. Thoroughly inspect the J1/P1 ECM connector, the J2/P2 ECM connector, and the connectors for each pressure sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

2. 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.

   Refer to Illustration 2.

3. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

4. 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 should be completely coupled and/or inserted. The harness and wiring should be free of corrosion, abrasion, and pinch points.

Results:

• OK - Proceed to Test Step 4.

• Not OK -

  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.Clear all logged diagnostic codes.

  Stop.

Test Step 4. Verify that the Diagnostic Code is Still Active

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

2. Monitor the "Active Diagnostic Code "screen on Cat ET. Record any active diagnostic codes.

3. Determine if the problem is related to an open circuit diagnostic code or a short circuit diagnostic code.

Expected Result:

Either a short circuit diagnostic code is active or an open circuit diagnostic code is active.

Results:

• SHORT Circuit - A short circuit diagnostic code is active at this time. Proceed to Test Step 5.

• OPEN Circuit - An open circuit diagnostic code is active at this time. Proceed to Test Step 6.

Test Step 5. Disconnect the Sensor in Order to Create an Open Circuit

1. Turn the keyswitch to the OFF position.

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

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

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

Expected Result:

An open circuit diagnostic code for the disconnected sensor is now active.

Results:

• OK - A short circuit diagnostic code was active before disconnecting the sensor. An open circuit diagnostic code became active after disconnecting the sensor. Proceed to Test Step 7.

• Not OK - There is a short circuit between the sensor harness connector and the ECM. Leave the sensor disconnected. Proceed to Test Step 9.

Test Step 6. Measure the Sensor Supply Voltage

Illustration 3	g00810608
Terminals for pressure sensors

1. Turn the keyswitch to the OFF position.

2. Disconnect the sensor from the engine harness.

3. Turn the keyswitch to the ON position.

4. Measure the voltage from terminal A (Engine Pressure Sensor +5V) to terminal B (Engine Pressure Sensor Common) on the engine harness side of the connector.

   Refer to Illustration 3.

Expected Result:

The DC voltage from terminal A to terminal B measures 4.5 to 5.5 VDC.

Results:

• OK - The sensor supply voltage is correct. Proceed to Test Step 8.

• Not OK - The sensor supply voltage is out of range.

  Repair: Proceed to the following procedure: Troubleshooting, "5 Volt Engine Pressure Sensor Supply Circuit - Test"

  Stop.

Test Step 7. Determine if the Short Circuit is in the Connector or in the Sensor

1. Thoroughly inspect the connector for moisture.

2. Inspect the seals and reconnect the sensor.

3. If the short circuit diagnostic code reappears, the sensor or the pigtail harness connector is the problem.

   1. Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine.

4. Check for a short circuit diagnostic code while the new sensor is connected to the harness.

Expected Result:

The short circuit diagnostic code is not present when a new sensor is connected.

Results:

• OK - Verify that the repair eliminates the problem. Permanently install the new sensor. Clear the logged diagnostic codes. Stop.

• Not OK - Repair the engine harness connector. Stop.

Test Step 8. Create a Short Circuit Between the Signal and the Common Terminals at the Engine Harness Connector

Illustration 4	g00810608
Terminals for pressure sensors

1. Fabricate a jumper wire 150 mm (6 inch) long. Crimp a Deutsch terminal to both ends of the wire.

2. Turn the keyswitch to the ON position.

3. Monitor the "Active Diagnostic Code" screenon Cat ET before installing the jumper wire and after installing the jumper wire.

4. Install the jumper on the engine harness connector for the suspect sensor. Install one end of the jumper on terminal C (Signal). Install the other end of the jumper on terminal B (Common). Wait at least 15 seconds for activation of the short circuit diagnostic code.

   Refer to Illustration 4.

Expected Result:

A short circuit diagnostic code is active when the jumper is installed. An open circuit diagnostic code is active when the jumper is removed.

Results:

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

  Repair: Perform the following repair:

  1. Temporarily connect the suspect sensor.

  2. If the diagnostic code remains active, replace the sensor.

  3. Ensure that the diagnostic code is no longer active.

  4. Verify that the repair eliminates the problem.

  Stop.

• Not OK - The open circuit diagnostic code remains active when the jumper is installed. The most probable location for the open is in the sensor common or the sensor signal wire in the engine harness between the ECM and the sensor. Remove the jumper. Proceed to Test Step 9.

Test Step 9. Check the Operation of the ECM by Creating Open and Short Circuits at the ECM Connector

Illustration 5	g00904084
ECM connectors (ECM side)

1. Turn the keyswitch to the OFF position.

2. Disconnect the J1/P1 ECM connector and the J2/P2 ECM connector. Thoroughly inspect both halves of the connectors for signs of corrosion or moisture.

3. Reconnect the J1/P1 and J2/P2 ECM connectors.

4. Remove the signal wire for the suspect sensor from the appropriate ECM connector.

   Refer to Illustration 5.

5. Turn the keyswitch to the ON position. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 15 seconds for activation of the code.

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

6. Turn the keyswitch to the OFF position.

7. Fabricate a jumper wire approximately 150 mm (6 inch) long. Crimp a Deutsch socket on one end of the wire. Install an alligator clamp on the other end of the wire.

8. Insert the socket end of the jumper wire in the terminal for the suspect sensor signal. Connect the alligator clamp to the ECM ground strap.

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

9. Turn the keyswitch to the ON position. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 15 seconds for activation of the code.

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

Expected Result:

An open circuit diagnostic code is active when the sensor's signal wire is disconnected. A short circuit diagnostic code is active when the jumper wire is installed.

Results:

• OK - The ECM is operating properly. Proceed to Test Step 10.

• Not OK - The ECM is not responding properly.

  Repair: Perform the following repair:

  1. Temporarily connect a test ECM.

  2. Remove all jumpers and replace all connectors.

  3. Recheck the system for active diagnostic codes.

  4. Repeat the test step.

  5. If the problem is resolved with the test ECM, reconnect the suspect ECM.

  6. If the problem returns with the suspect ECM, replace the ECM.

  7. Verify that the repair eliminates the problem.

  Stop.

Test Step 10. Bypass the Wiring Harness Between the ECM and the Sensor Connector

1. Turn the keyswitch to the OFF position.

2. Remove the sensor signal wire from the ECM connector on the engine harness.

3. Remove the wire from terminal C (Signal) on the engine harness side of the sensor connector.

4. Fabricate a jumper wire that is long enough to reach from the ECM to the sensor connector or use an engine sensor harness bypass with 3 terminals.

   Note: If an engine sensor harness bypass is being made, crimp a Deutsch socket on one end in order to connect to the ECM. Crimp either a Deutsch pin or a Deutsch socket on the other end, as required.

5. Insert the engine sensor harness bypass into the appropriate terminal in the ECM connector for the suspect sensor's signal wire. Insert the other end of the engine sensor harness bypass into terminal C (Signal) of the sensor connector.

6. Turn the keyswitch to the ON position.

7. Monitor the "Active Diagnostic Code" screen on Cat ET for either the open circuit diagnostic code or the short circuit diagnostic code for the sensor.

Expected Result:

The diagnostic code disappears when the jumper or the bypass is installed.

Results:

• OK - There is a problem in the wiring harness.

  Repair: Repair the circuit and clear all diagnostic codes.Verify that the repair eliminates the problem.

  Stop.

• Not OK - Restart this procedure and carefully perform each step. Stop.