G3500 A3 Engines Caterpillar

Use this procedure to troubleshoot the following diagnostic codes:

• 41-3 8 Volt DC Supply voltage above normal

• 41-4 8 Volt DC Supply voltage below normal

The Electronic Control Module (ECM) supplies 8.0 ± 0.8 VDC to the following sensors:

• Sensor for engine coolant pressure (outlet)

• Sensor for inlet air pressure

• Both of the detonation sensors

An active 41-3 or 41-4 diagnostic code is probably caused by a short circuit or an open circuit in a harness. The next likely cause is a sensor problem. The least likely cause is a problem with the ECM.

This troubleshooting procedure may generate additional diagnostic codes. Continue troubleshooting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.

Illustration 1	g01250267
Schematic for the 8 volt supply

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Set the engine control to the OFF/RESET position.

   Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".

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   Illustration 2	g01250269
   Location of the sensors for the sensor supply circuit (typical front engine view) (1) Inlet air pressure sensor

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   Illustration 3	g01250268
   Location of the sensors for the sensor supply circuit (typical top engine view) (2) Engine coolant pressure sensor (outlet)

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   Illustration 4	g01250270
   Location of the sensors for the sensor supply circuit (typical right side engine view) (3) Detonation sensor

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   Illustration 5	g01394859
   Location of the ECM connectors for the sensor supply circuit (typical left front engine view) (4) J2/P2 ECM connectors (5) J1/P1 ECM connectors

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   Illustration 6	g01393791
   Location of the engine interface connectors for the sensor supply circuit (typical left rear engine view) (6) Engine interface connectors

2. Thoroughly inspect the connectors for sensors (1), (2), and (3). Also, thoroughly inspect ECM connectors (4) and (5), and interface connector (6).

   1. Check the allen head screws for each of the ECM connectors for the proper torque.

   2. Check the harness and wiring for abrasion and for pinch points from each 8 volt sensor to the ECM.

Expected Result:

All of the connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.

Results:

• OK - All of the connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points. The components are in good condition with proper connections. Proceed to Test Step 2.

• Not OK - At least one of the connectors, pins, and sockets are not connected properly. At least one of the connectors and/or the wiring has corrosion, abrasion, and/or pinch points.

  Repair: Perform the necessary repairs and/or replace parts, if necessary.

  STOP

Test Step 2. Check for Diagnostic Codes

1. Establish communication between Cat ET and the engine ECM. Refer to Troubleshooting, "Electronic Service Tools", if necessary.

2. Set the engine control to the STOP position.

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

   • 41-3 8 Volt DC Supply : Voltage Above Normal

   • 41-4 8 Volt DC Supply : Voltage Below Normal

4. Observe the "Logged Diagnostic" screen on Cat ET. Look for the same codes.

Expected Result:

The 41-3 code or the 41-4 code is not active.

Results:

• No codes - The 41-3 code or the 41-4 code is not active. The +8 volt sensor supply is operating correctly at this time.

  STOP

• Active code - The 41-3 code or the 41-4 code is active. Proceed to Test Step 3.

• Logged code - The 41-3 code or the 41-4 code is not active. However, there is at least one logged code for the 8 volt sensor supply.

  Repair: There may be a problem with the wiring and/or a connector. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  Verify that the wiring and/or connectors are OK. Check for diagnostic codes again. Proceed to Test Step 3, if necessary.

Test Step 3. Disconnect the 8 Volt Sensors and Look for Active Diagnostic Codes

1. Turn on the "Active Diagnostic" screen on Cat ET. Verify that the 41-3 or 41-4 code is active.

2. Disconnect each 8 volt sensor one at a time. After you disconnect each sensor, wait for at least 30 seconds and then observe the "Active Diagnostic" screen on Cat ET.

   Note: A -4 code will be generated for each sensor that is disconnected. This is normal. Clear the codes after you complete this procedure.

Expected Result:

The original diagnostic code is deactivated when a particular sensor is disconnected.

Results:

• OK - The "8 Volt DC Supply" diagnostic code is deactivated when a particular sensor is disconnected. The sensor and/or the wiring for the sensor has a short circuit.

  Repair: Perform the following procedure:

  1. Connect the suspect sensor. Verify that the diagnostic code recurs.

  2. Disconnect the suspect sensor. Verify that the diagnostic code is deactivated.

     If these conditions are true, replace the sensor.

  3. Clear all of the diagnostic codes. Verify that the problem is resolved.

  STOP

• Not OK - The original diagnostic code is still active when all of the 8 volt sensors are disconnected. Do not connect the sensors. Proceed to Test Step 4.

Test Step 4. Isolate the Wiring Harnesses from the ECM

1. Set the engine control to the OFF/RESET position.

2. Remove the wires from the following terminal locations at the ECM connector:

   • P1-4

   • P2-57

   • P2-65

3. Set the engine control to the STOP position.

4. Wait for at least 30 seconds and then observe the "Active Diagnostics" screen on Cat ET. Determine if a 41-3 code or a 41-4 code is active.

5. Restore the wiring at the ECM to the original configuration.

Expected Result:

A 41-3 code or a 41-4 code is not active at this time.

Results:

• OK - A 41-3 code or a 41-4 code is not active at this time. Isolating the ECM from the circuit eliminated the active diagnostic code. There is a problem in a connector and/or the wiring in a harness. Proceed to Test Step 5.

• Not OK - There is an active 41-3 or 41-4 code.

  Repair: Disconnecting all of the 8 volt wiring from the ECM did not eliminate the original diagnostic code. There may be a problem with the ECM. Perform the following procedure:

  1. Temporarily connect a test ECM.

     Refer to Troubleshooting, "Replacing the ECM".

  2. Recheck the circuit in order to ensure that the original problem has been resolved.

     If the problem is resolved with the test ECM, install the suspect ECM. If the problem returns with the suspect ECM, replace the ECM. Verify that the problem is resolved.

     If the problem is not resolved with the test ECM, install the original ECM. There is a problem in the wiring.

  STOP

Test Step 5. Identify the Problem in the Harness

1. Disconnect the detonation sensors.

2. Verify that the diagnostic code for the 8 volt supply is active.

3. Use 7X-1710 Multimeter Probes to measure the voltage at terminal locations P1-4 and P1-5.

   Note: The voltage reading will depend on the problem with the wiring. The voltage reading will be low or high.

4. Carefully wiggle the wiring in the engine harness while you monitor the voltage indication on the multimeter. Look for approximately 8 VDC on the circuit. Be sure to wiggle the wiring near each of the connectors that are associated with the 8 volt supply.

5. Restore the wiring to the original configuration.

Expected Result:

The voltage reading changes to approximately 8 VDC when the wiring is wiggled at a particular location.

Results:

• OK - The voltage reading changes to approximately 8 VDC when the wiring is wiggled at a particular location.

  Repair: There is a problem in the harness near this location. Identify the problem with the harness. Repair the harness, when possible. Replace parts, if necessary. Verify that the problem is resolved.

  STOP