C-12 Generator Set Engine Caterpillar

Use this procedure to troubleshoot any suspect problems with the +5 V analog sensor supply.

This procedure covers the following diagnostic codes:

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

• 262-04 5 Volt Sensor DC Power Supply short to ground

The Electronic Control Module (ECM) creates a regulated voltage of 5.0 ± 0.2 VDC that is supplied to these sensors:

• Engine oil pressure sensor

• Turbocharger outlet pressure sensor

• Fuel pressure sensor

• Atmospheric pressure sensor

• Turbocharger Inlet pressure sensor

The supply for the +5 V engine pressure sensor is routed from the ECM to terminal A of each pressure sensor connector. The sensor return from the ECM connector goes to terminal B of each sensor connector. The 5 V sensor supply is output short circuit protected. A short circuit to the battery will not damage the circuit inside the ECM.

A +5 V diagnostic code is probably caused by a short circuit to ground or a short circuit to another voltage source in the harness. The next likely cause is a problem with a sensor. The least likely cause is a problem with 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 5 V sensor supply and check for any active diagnostic codes for the sensor in order to determine if a sensor has failed.

A +5 V diagnostic code is probably caused by a short circuit to ground or a short circuit to another voltage source in the harness. The next likely cause is a problem with a sensor. The least likely cause is a problem with the ECM.

Illustration 1	g01197359
Typical schematic

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove electrical power from the ECM.

2. Thoroughly inspect the J1/P1 or J2/P2 ECM connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect".

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Illustration 2	g01192209
P1 terminals that are associated with the 5 volt supply (P1-2) +5 VDC (P1-3) Return

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Illustration 3	g01197317
P2 terminals that are associated with the 5 volt supply (P2-2) +5 VDC (P2-3) Return

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Illustration 4	g01123211
Connectors for the sensors (A) Supply (B) Return (C) Signal

3. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the 5 volt supply.

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

5. Check the harness and the wiring for abrasion and for pinch points from each sensor back to the ECM.

Expected Result:

All of the 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 - The connectors and/or wiring are not OK.

  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. Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check for Active Diagnostic Codes

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

2. Restore electrical power to the ECM.

3. Use Cat ET to check for active diagnostic codes. Wait at least 30 seconds so that any codes may become active. Check for these codes:
   • 262-03

   • 262-04

Expected Result:

No diagnostic codes are active.

Results:

• OK - No diagnostic codes are active.

  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

• Not OK - Either the 262-03 or 262-04 diagnostic code is active at this time. Proceed to Test Step 3.

Test Step 3. Disconnect the Pressure Sensors and Check for Active Diagnostic Codes

1. Restore electrical power to the engine ECM.

2. Monitor the active diagnostic code screen on Cat ET while you disconnect each pressure sensor connector. Check for an active 262-03 code or an active 262-04 code.

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

   1. Disconnect the following sensors one at a time:
      • Engine oil pressure sensor

      • Turbocharger outlet pressure sensor

      • Fuel pressure sensor

      • Atmospheric pressure sensor

      • Turbocharger Inlet pressure sensor

3. Remove electrical power from the ECM.

Expected Result:

The diagnostic code deactivates when a particular sensor is disconnected.

Results:

• OK - The 262-03 or 262-04 diagnostic code deactivates when a particular sensor is disconnected.

  Repair: Connect the suspect sensor. If the code returns, replace the sensor. Connect all of the connectors. Verify that the problem is resolved.

  STOP

• Not OK - The 262-03 or 262-04 diagnostic code remains active after all of the sensors are disconnected. Leave the sensors disconnected. The sensors are not the cause of the diagnostic code. Proceed to Test Step 4.

Test Step 4. Check the Supply Voltages at the ECM

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

2. Fabricate four jumper wires that are long enough to be used to measure the supply voltage at the ECM connectors. Crimp connector sockets to one end of each jumper wire.

3. Remove the wires from terminal locations P1-2 (5 V sensor supply) and P1-3 (sensor return). Install a jumper wire into each of these terminal locations.

4. Remove the wires from terminal locations P2-2 (5 V sensor supply) and P2-3 (sensor return). Install a jumper wire into each of these terminal locations.

5. Connect ECM connectors J1/P1 and J2/P2.

6. Restore electrical power to the engine ECM.

7. Measure the voltage between the jumper wire in P1-2 (5 V sensor supply) and the jumper wire in P1-3 (sensor return).

8. Measure the voltage between the jumper wire in P2-2 (5 V sensor supply) and the jumper wire in P2-3 (sensor return).

9. Remove electrical power from the ECM.

10. Restore the wiring to the original configuration.

Expected Result:

The voltage measurement is 5.0 ± 0.2 VDC.

Results:

• OK - The voltage measurement is 5.0 ± 0.2 VDC. The ECM is operating correctly.

  Repair: One of the supply wires is shorted to another wire in the harness or one of the supply wires is shorted to engine ground. For each individual supply wire in the harness, perform the following test steps:

  1. One at a time, install the wiring for each 5 V supply while you check Cat ET for an active 262-03 or 262-04 diagnostic code.

     1. Disconnect the particular ECM connectors.

     2. Install the wires that were removed for the 5 V supply at this ECM connector. Refer to Illustration 1 for wiring information.

     3. Connect the ECM connectors.

     4. Restore electrical power to the engine ECM.

     5. Monitor the active diagnostic code screen on Cat ET. Check for an active 262-03 code or an active 262-04 code.

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

     6. If a diagnostic code becomes active for this 5 V supply, there is a problem in this harness between the ECM and the sensor connector.

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

  STOP

• Not OK - The voltage measurement is not 5.0 ± 0.2 VDC.

  Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM".

  STOP