G3520B Industrial Engine Caterpillar

The master Electronic Control Module (ECM) supplies 5.0 ± 0.5 VDC to the sensors for these parameters:

• Inlet air temperature

• Engine oil temperature

• Unfiltered engine oil pressure

• Filtered engine oil pressure

• Humidity

The master ECM also provides 5.0 ± 0.5 VDC to the "DESIRED SPEED" potentiometer (if equipped). A "+5 Volt Sensor DC Power Supply short to ground" diagnostic code will be activated if both of these conditions occur:

• The desired speed signal wire is shorted to ground.

• The "DESIRED SPEED" potentiometer is near the maximum desired speed or at the maximum desired speed.

Terminals J1-2 and J1-18 are connected together inside the master ECM. A short circuit on one of these terminals will cause a short circuit on the other terminal.

A "+5 V sensor supply" diagnostic code is probably caused by a short circuit or by an open circuit in a harness. The next likely cause is a sensor problem. The least likely cause is a problem with the master ECM.

Logged diagnostic codes provide a historical record. Before you begin this procedure, use the Caterpillar Electronic Technician (ET) to print the logged codes to a file.

This troubleshooting procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.

Illustration 1	g01090680
Schematic for the 5 volt supply

Test Step 1. Inspect the Electrical Connectors and Wiring

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

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

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Illustration 2	g01085086
Terminal box for the master ECM (1) J1/P1 connectors for the master ECM (2) J5/P5 connector for the customer's connections (3) J10/P10 connectors for the harness to the optional control panel (4) J7/P7 connectors for the harness to the 5 volt sensors

2. Thoroughly inspect each of the following connectors:
   • J1/P1 connectors

   • J5/P5, J7/P7, and J10/P10 connectors on the terminal box

   1. Check the torque of the allen head screws for the ECM connectors. The proper torque is 6 ± 1 N·m (55 ± 9 lb in).
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   Illustration 3	g01085957
   Harness side of the P1 connector (P1-2) 5 volt supply for the sensors (P1-18) 5 volt supply for the desired speed potentiometer

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   Illustration 4	g01085961
   Harness side of the J5 connector (J5-10) 5 volt supply for the desired speed potentiometer

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   Illustration 5	g01085962
   Harness side of the P7 connector (P7-A) 5 volt supply for the sensor for inlet manifold air temperature (P7-B) 5 volt supply for the filtered engine oil pressure sensor (P7-D) 5 volt supply for the humidity sensor (P7-E) 5 volt supply for the engine oil temperature sensor (P7-K) 5 volt supply for the unfiltered engine oil pressure sensor

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   Illustration 6	g01085964
   Harness side of the P10 connector (P10-N) 5 volt supply for the desired speed potentiometer

   2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the 5 volt sensors.
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   Illustration 7	g01085287
   Right side view (5) Inlet air temperature sensor

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   Illustration 8	g01085298
   Left side view (6) Unfiltered oil pressure sensor (7) Filtered oil pressure sensor (8) Humidity sensor (9) Engine oil temperature sensor

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   Illustration 9	g01085322
   Terminal strip inside the optional control panel

   3. Check the harness and wiring for corrosion, for abrasion, and for pinch points from each 5 volt sensor to the master ECM.

Expected Result:

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

Results:

• OK - All 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, or sockets are not connected properly. At least one of the connectors and 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. Connect Cat ET to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

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Illustration 10	g01085325
Desired speed potentiometer on the optional control panel

2. Rotate the "DESIRED SPEED" potentiometer (if equipped) counterclockwise to the minimum speed position.

3. Restore the electrical power to the engine. Set the engine control to the STOP mode.

4. Observe the "Active Diagnostic" screen on Cat ET. Wait at least 30 seconds so that any codes may become activated. Look for these codes:
   • 262-03 5 Volt Sensor DC Power Supply short to +batt

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

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

Expected Result:

The 262-03 code or the 262-04 code is not active or logged.

Results:

• No codes - There are no active codes or logged codes. If the engine is equipped with a "DESIRED SPEED" potentiometer, proceed to Test Step 3. Otherwise, the 5 volt sensor voltage supply is operating correctly at this time. Resume normal operation. STOP.

• Active code - The 262-03 code or the 262-04 code is active. Proceed to Test Step 5.

• Logged code - The 262-03 code or the 262-04 code is not active. However, there is at least one logged code for the 5 volt sensor supply.

  Repair: There may be a problem with the wiring and/or with 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. Check the Analog Speed Circuit

Rotate the "DESIRED SPEED" potentiometer (if equipped) clockwise to the maximum speed position. Look for these codes:

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

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

Expected Result:

The 262-03 code or the 262-04 code is not active.

Results:

• No codes - Rotating the "DESIRED SPEED" potentiometer clockwise to the maximum speed position did not cause an active code. The +5 V sensor voltage supply is operating correctly at this time. Resume normal operation. Stop.

• Active code - Rotating the "DESIRED SPEED" potentiometer clockwise to the maximum speed position caused an active code. There is a problem with the analog speed circuit. Proceed to Test Step 4.

Test Step 4. Check the Wiring for the "DESIRED SPEED" Potentiometer

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

2. Label the wiring that is connected to the "DESIRED SPEED" potentiometer. Disconnect the wiring from the "DESIRED SPEED" potentiometer.

3. Disconnect the P1 connector.

4. Measure the resistance between terminal P1-16 and all of the other terminals on the P1 connector.

Expected Result:

Each check of the resistance is greater than 20,000 Ohms.

Results:

• OK - Each check of the resistance is greater than 20,000 Ohms. The wiring for the "DESIRED SPEED" potentiometer appears to be OK.

  Repair: The "DESIRED SPEED" potentiometer may have a problem. Perform the following procedure:

  1. Check the "DESIRED SPEED" potentiometer in order to ensure that the potentiometer does not have an internal short circuit. Replace the "DESIRED SPEED" potentiometer, if necessary. Continue with this procedure when the "DESIRED SPEED" potentiometer is operating correctly.

  2. Reconnect the wiring to the "DESIRED SPEED" potentiometer. Be sure to connect the wires to the appropriate terminals.

  3. Reconnect the P1 connector to the ECM.

  4. Perform this entire procedure again. Verify that the original problem is resolved.

  Stop.

• Not OK - At least one check of the resistance is less than 20,000 Ohms. There is a problem with the wiring for the "DESIRED SPEED" potentiometer. The problem could be between the P1 connector and the J10 connector. Alternatively, the problem could be in the P10 connector or in the wiring that is connected to the P10 connector.

  Repair: Perform any necessary repairs or replace parts, if necessary.

  Stop.

Test Step 5. Isolate the Wiring Harnesses from the Master ECM

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

2. Reconnect the P1 connector to the master ECM.

3. Use a 151-6320 Wire Removal Tool to remove terminals P1-2 and P1-18.

4. Restore the electrical power to the engine. Set the engine control to the STOP mode.

5. Use Cat ET to look for diagnostic codes.

Expected Result:

No active codes

Results:

• No codes - The 262-03 code or the 262-04 code is not active. Disconnecting all of the 5 volt wiring from the master ECM eliminated the active "5 Volt Sensor Supply" diagnostic code. There is a problem with a connector and/or with the wiring in a harness. Proceed to Test Step 6.

• Active code - The 262-03 code or the 262-04 code is active. Disconnecting all of the 5 volt wiring from the master ECM did not eliminate the 5 volt diagnostic code. There may be a problem with the ECM.

  Repair: It is unlikely that the master ECM has failed. Exit this procedure and perform this procedure again. If the problem is not resolved, perform the following steps:Temporarily install a new master ECM. Refer to Troubleshooting, "Replacing the ECM".If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM. Refer to Troubleshooting, "Replacing the ECM".

  Stop.

Test Step 6. Connect the 5 Volt Wiring for the Analog Speed Circuit to the Master ECM

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

2. Insert terminal 18 into the P1 connector. Pull on the wire in order to verify that the terminal is fully inserted into the connector.

3. Rotate the "DESIRED SPEED" potentiometer clockwise to the maximum speed position.

4. Restore the electrical power to the engine. Set the engine control to the STOP mode.

5. Use Cat ET to look for diagnostic codes.

Expected Result:

No active codes

Results:

• No codes - The 262-03 code or the 262-04 code is not active. Connecting the wiring for the analog speed circuit to the master ECM did not cause a diagnostic code. The wiring for the analog speed circuit appears to be OK. Proceed to Test Step 7.

• Active codes - The 262-03 code or the 262-04 code is active. Connecting the wiring for the analog speed circuit to the master ECM caused a diagnostic code. Proceed to Test Step 4.

Test Step 7. Connect the 5 Volt Wiring for the Sensors to the Master ECM

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

2. Insert terminal 2 into the P1 connector. Pull on the wire in order to verify that the terminal is fully inserted into the connector.

3. Restore the electrical power to the engine. Set the engine control to the STOP mode.

4. Use Cat ET to look for diagnostic codes.

Expected Result:

No active codes

Results:

• No codes - The 262-03 code or the 262-04 code is not active. Connecting the 5 VDC for the sensors did not cause a diagnostic code. The problem appears to be resolved.

  Repair: The initial diagnostic code was probably caused by a poor electrical connection. Resume normal operation.

  Stop.

• Active code - The 262-03 code or the 262-04 code is active. Connecting the 5 VDC for the sensors caused a diagnostic code. Proceed to Test Step 8.

Test Step 8. Disconnect the 5 Volt Sensors and Look for Active Diagnostic Codes.

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

2. Disconnect the sensors for the following parameters:
   • Inlet air temperature

   • Engine oil temperature

   • Unfiltered engine oil pressure

   • Filtered engine oil pressure

   • Humidity (if equipped)

3. Restore the electrical power to the engine. Set the engine control to the STOP mode.

   Note: An "Open Circuit" code will be generated for each sensor that is disconnected. This is normal. Clear the codes after you complete this procedure.

4. Observe the "Active Diagnostic" screen on Cat ET. Verify that the 262-03 code or the 262-04 code is not active.

5. Reconnect the sensors for the following parameters one at a time. After you reconnect each sensor, wait for at least 30 seconds and then observe the "Active Diagnostic" screen on Cat ET.
   • Inlet air temperature

   • Engine oil temperature

   • Unfiltered engine oil pressure

   • Filtered engine oil pressure

   • Humidity

Expected Result:

The original "5 Volt Sensor" diagnostic code is activated when a particular sensor is disconnected.

Results:

• Yes - The original "5 Volt Sensor" diagnostic code is activated when a particular sensor is reconnected. The sensor and/or the wiring for the sensor has a short circuit.

  Repair: Perform the following procedure:

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

  2. Disconnect the suspect sensor.

  3. Set the engine control to the STOP mode. Use Cat ET to clear the logged 262-03 or 262-04 code.

  4. Reconnect the suspect sensor. Verify that the diagnostic code recurs.

     If these conditions are true, replace the sensor.

  5. Clear all of the diagnostic codes. Verify that the problem is eliminated.

  Stop.

• No - The original "5 Volt Sensor" diagnostic code was still active while all of the 5 volt sensors were disconnected. Do not reconnect the sensors. Proceed to Test Step 9.

Test Step 9. Check the Harnesses

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

2. Disconnect the P1 connector. Verify that all of the sensors for the following parameters are disconnected from the engine harness:
   • Inlet air temperature

   • Engine oil temperature

   • Unfiltered engine oil pressure

   • Filtered engine oil pressure

   • Humidity

3. Measure the resistance between terminal P1-2 and each of the remaining terminals on the P1 connector. During each measurement, wiggle the harnesses in order to check for an intermittent problem with the harness. Be sure to wiggle the harnesses near each of the connectors for the disconnected sensors. Also, wiggle the harness at the P7 connector.

Expected Result:

Each check of the resistance is greater than 20,000 Ohms.

Results:

• OK - Each check of the resistance is greater than 20,000 Ohms. The 5 volt wires in the engine harnesses do not have a problem. The problem appears to be resolved. The initial diagnostic code was probably caused by a poor electrical connection.

  Repair: Reconnect all of the connectors. Resume normal operation.

  Stop.

• Not OK - At least one check of the resistance is less than 20,000 Ohms. There is a problem with a connector and/or with at least one of the 5 volt wires in a harness.

  Repair: The problem may be between the P1 connector and the P7 connector. Alternatively, The problem may be in the engine harness that is connected to the P7 connector.Repair the connection or the wire, when possible. Replace parts, if necessary. Verify that the original problem is resolved.

  Stop.