3176C Engines for Caterpillar Built Machines Caterpillar

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

Use this procedure to troubleshoot the system when one of the following diagnostic codes is active or easily repeated:

• 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) supplies a regulated voltage of 5.0 ± 0.2 VDC to the following sensors:

• Engine oil pressure sensor

• Turbocharger outlet 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.

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	g01276328
Schematic for the 5 volt pressure sensor supply

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	g01123211
Connectors for the sensors (A) +5 V Sensor supply (B) Sensor return (C) Signal

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Illustration 7	g01159881
Sensor connector (Terminal A) +5 V supply (Terminal B) Sensor return (Terminal C) Sensor 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 of 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 or 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 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. Monitor the active diagnostic code screen on Cat ET. Check for an active 262-03 code and an active 262-04 code.

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

4. Remove electrical power from the ECM.

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 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

      • Atmospheric pressure sensor

      • Turbocharger inlet pressure sensor

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. The sensors are not the cause of the diagnostic code. Leave the sensors disconnected. Proceed to Test Step 4.

Test Step 4. Check the Supply Voltage at the ECM

1. Remove electrical power from the ECM.

2. Disconnect the J1/P1 ECM connectors.

3. Disconnect the J2/P2 ECM connectors.

4. Fabricate four jumper wires that are long enough to be used as test leads at the ECM connectors. Crimp connector sockets to one end of each jumper wire.

5. 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.

6. 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.

7. Connect the J1/P1 and J2/P2 ECM connectors.

8. Restore electrical power to the ECM.

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

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

11. Remove electrical power from the ECM.

Expected Result:

The voltage measurement is 5.0 ± 0.2 VDC at both ECM connectors.

Results:

• OK - The voltage measurement is 5.0 ± 0.2 VDC at both ECM connectors.

  Repair: The ECM is operating correctly. The supply wires are shorted to another wire in the harness or the supply wires are shorted to engine ground. 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 at one or both of the ECM connectors.

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

  STOP