3126B and 3126E On-highway Engines Caterpillar

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

• 232-03 5 Volt Supply voltage high

• 232-04 5 Volt Supply voltage low

Also, use this procedure to troubleshoot the system when you have been directed here by another troubleshooting procedure.

The Engine Control Module (ECM) supplies the following sensors with regulated 5.0 ± 0.2 VDC from the same power supply:

• Boost pressure sensor

• Atmospheric pressure sensor (specific ratings only)

• Engine oil pressure sensor (optional)

• Injection actuation pressure sensor

The power supply for the pressure sensors is routed from J2-2 (+5 V pressure sensor supply) to terminal "A" of each pressure sensor connector.

The most likely cause of a diagnostic code for +5 V pressure sensor supply is a short circuit or an open circuit in the harness. The next probable cause is a faulty sensor and the least probable cause is the ECM.

Illustration 1	g01151304
Schematic for the +5 V pressure sensor supply

Test Step 1. Inspect the Electrical Connectors and the Wiring

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Illustration 2	g01151317
Left side engine view (typical example) (1) Injection actuation pressure sensor (2) Atmospheric pressure sensor (3) Boost pressure sensor (4) Engine oil pressure sensor (option) (5) J2/P2 ECM connector

1. Thoroughly inspect ECM connector (5). Also inspect the connectors for pressure sensors (1), (2), (3), and (4). Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

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Illustration 3	g01151333
P2 ECM connector (P2-2) +5 V pressure sensor supply (P2-3) Pressure sensor return (P2-41) +5 V oil pressure sensor supply (P2-42) Oil pressure sensor return

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

2. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the +5 V pressure sensor supply.

3. Check the torque of the allen head screw on the ECM connectors and the customer connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

4. Check the harness and wiring for abrasion and for pinch points from each pressure sensor 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 - Proceed to Test Step 2.

• Not OK -

  Repair: Perform the following 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 ignition key switch to the ON position.

3. Monitor the "Active Diagnostic Code" screen of Cat ET. Wait at least 15 seconds in order for the diagnostic codes to become active. Check and record active diagnostic codes.

Look for these codes:

• 232-03

• 232-04

Expected Result:

One of the above codes is active.

Results:

• Active 232-03 code - A 232-03 diagnostic code is active. Proceed to Test Step 3.

• Active 232-04 code - A 232-04 diagnostic code is active. Proceed to Test Step 5.

• No active codes - None of the above 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

Test Step 3. Check the Voltage on the +5 V Supply Wire

1. Turn the keyswitch to the OFF position.

2. Disconnect the harness connectors for the following sensors:
   • Boost pressure sensor

   • Atmospheric pressure sensor (specific ratings only)

   • Engine oil pressure sensor (optional)

   • Injection actuation 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.

Expected Result:

Each voltage measurement is 5.0 ± 0.2 VDC.

Results:

• OK - Each voltage measurement is 5.0 ± 0.2 VDC. The sensors are receiving the correct voltage.

  Repair: Connect all of the sensor connectors. Clear all diagnostic codes. Check the engine again 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. 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. Disconnect the following sensors one at a time. Wait for 15 seconds after you disconnect each sensor. Check for the active 232-04 diagnostic code again.
   • Boost pressure sensor

   • Atmospheric pressure sensor (specific ratings only)

   • Engine oil pressure sensor (optional)

   • Injection actuation pressure sensor

Expected Result:

The 232-04 diagnostic code deactivates when a particular sensor is disconnected.

Results:

• OK - The 232-04 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 232-04 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

1. Turn the keyswitch to the OFF position.

2. Disconnect the J2/P2 ECM connector. Disconnect the J1/P1 ECM connector.

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

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

4. Check for a short circuit in the harness.

   1. Measure the resistance between terminal P2-2 (+5 V pressure sensor supply) and all of the other terminals on the P1 ECM connector and the P2 ECM connector.

   2. Measure the resistance between terminal P2-41 (+5 V oil pressure sensor supply) and all of the other terminals on the P1 ECM connector and the P2 ECM connector.

5. Measure the resistance between terminal P2-2 and the engine ground. Also, 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. A +5 V supply wire has a short circuit that is in the harness. There may be a problem with 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 6. Check the +5 V Supply and the Sensor Common for an Open Circuit

1. Install a wire jumper between terminals P2-2 (+5 V pressure sensor supply) and P2-3 (pressure sensor return).

2. Install a wire jumper between terminals P2-41 (+5 V oil pressure sensor supply) and P1-42 (oil pressure sensor return).

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

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

Expected Result:

Each resistance measurement is less than five Ohms.

Results:

• OK - Each measurement is less than five Ohms. There is no open circuit. 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 an open circuit. 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 pressure sensor supply) from the ECM connector. Install a wire jumper with socket terminals on both ends into P2-2.

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

3. Connect ECM connectors J2/P2.

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. The ECM is OK.

  Repair: Clear all diagnostic codes. Check for active diagnostic codes. There may be an intermittent electrical problem. 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. The ECM is not operating correctly.

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

  STOP