3126B Machine Engines Caterpillar

The Electronic Control Module (ECM) creates a regulated voltage of 5.0 ± 0.2 VDC that is supplied to terminal A of the harness connectors for these sensors:

• Fuel pressure sensor

• Engine oil pressure sensor

• Injection actuation pressure sensor

• Boost pressure sensor

• Atmospheric pressure sensor

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

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	g01330734
Schematic for pressure sensor supply

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Turn the keyswitch to the OFF position.
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   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".
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   Illustration 3	g01330756
   P2 ECM connector (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

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   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 for Active Diagnostic Codes

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

2. Turn the keyswitch to the ON position.

3. Observe the "Active Diagnostic" screen on Cat ET. Wait at least 30 seconds so that any codes may become active. Look for these codes:

   • 262-03

   • 262-04

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

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

• Active -03 code - A -03 diagnostic code is active. Proceed to Test Step 3.

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

Test Step 3. 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:

   • Fuel pressure sensor

   • Engine oil pressure sensor

   • Injection actuation pressure sensor

   • Boost pressure sensor

   • Atmospheric 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.

  Repair: Replace all wires to the original configuration. Clear all diagnostic codes. Check for active diagnostic codes. If the problem is intermittent, refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - At least one voltage measurement is not 5.0 ± 0.2 VDC. There is a problem with the wiring or with the ECM. Proceed to Test Step 5.

Test Step 4. Disconnect the +5 V Pressure Sensors and Check for Active Diagnostic Codes

1. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes.

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

2. Disconnect the following sensors one at a time at the sensor connector:

   • Fuel pressure sensor

   • Engine oil pressure sensor

   • Injection actuation pressure sensor

   • Boost pressure sensor

   • Atmospheric pressure sensor

Expected Result:

The 262-04 diagnostic code deactivates when a particular sensor is disconnected.

Results:

• OK - The 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 262-04 diagnostic code remains after all of the sensors are disconnected. Leave the sensors disconnected. Proceed to Test Step 5.

Test Step 5. Check the +5 V Supply Wire for a Short in the Wiring Harness

1. Turn the keyswitch to the OFF position.

2. Disconnect the J2/P2 ECM connectors.

3. Verify that all of the pressure sensors are disconnected.

   Note: Wiggle the harness during the following measurements in order to reveal any intermittent short condition.

4. Measure the resistance between terminal P2-2 (+5 V supply) and all of the other terminals on the P2 ECM connectors.

5. Measure the resistance between terminal P2-41 (+5 V supply) and all of the other terminals on the P2 ECM connectors.

6. Measure the resistance between terminal P2-2 and the engine ground.

7. Measure the resistance between terminal P2-41 and the engine ground.

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 of the resistance measurements does not indicate an open circuit.

  Repair: A +5 V supply wire has a problem. There may be a problem with a connector. Repair the wire and/or the connector, when possible. Replace parts, if necessary. Verify that the problem is resolved.

  STOP

Test Step 6. Check the +5 V Supply and the Sensor Return for an Open Circuit

1. Fabricate two jumper wires that can be used to jumper two terminals at the ECM connector. Crimp connector pins to each end of the jumper wire.

2. Install one of the jumper wires between P2-2 (+5 V supply) and P2-3 (sensor return).

3. Install the other wire jumper between P2-41 (+5 V supply) and P2-42 (sensor return).

   Note: Wiggle the harness during the following measurements in order to reveal any intermittent short condition.

4. Measure the resistance between terminals A and B at the harness connector for each pressure sensor.

5. Remove the wire jumpers.

Expected Result:

The resistance is less than five Ohms for each measurement.

Results:

• OK - Each measurement is less than five Ohms. Proceed to Test Step 7.

• Not OK - At least one resistance measurement is greater than five Ohms. The +5 V supply wire or the return wire has excessive resistance. There may be a problem in a connector.

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

  STOP

Test Step 7. Check the +5 V Supply at the ECM

1. Remove terminal P2-2 (+5 V supply) from the P2 connector. Install a wire jumper with socket terminals on both ends into the P2-2 location.

2. Remove terminal P2-41 (+5 V supply) from the P2 connector. Install a wire jumper with socket terminals on both ends into the P2-41 location.

3. Connect the J2/P2 ECM connectors.

4. Turn the keyswitch to the ON position.

5. Measure the voltage between the wire jumper in P2-2 and the engine ground.

6. Measure the voltage between the wire jumper in P2-41 and the engine ground.

7. Turn the keyswitch to the OFF position.

8. Restore both wires to the original configuration.

Expected Result:

Both voltage measurements are 5.0 ± 0.2 VDC.

Results:

• OK - Both voltage measurements are 5.0 ± 0.2 VDC.

  Repair: Clear all diagnostic codes. Check for active diagnostic codes. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - At least one voltage measurement is not 5.0 ± 0.2 VDC.

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

  STOP