G3516C, G3516E, and G3512E Generator Set Engines Caterpillar

Use this procedure to troubleshoot suspect problems with the circuit for the sensor supplies.

This procedure covers the following diagnostic codes:

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

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

• 145-3 12 Volt DC Power Supply : Voltage Above Normal

• 145-4 12 Volt DC Power Supply : Voltage Below Normal

• 262-3 5 Volt Sensor DC Power Supply : Voltage Above Normal

• 262-4 5 Volt Sensor DC Power Supply : Voltage Below Normal

The Electronic Control Modules (ECM) supply operating voltage to the engine's sensors. Refer to Illustration 1 for details.

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

The most likely cause of a diagnostic code are a poor connection or a problem in a wiring harness. The next likely cause is a problem with a sensor. The least likely cause is a problem with the ECM.

Logged diagnostic codes provide a historical record. Before you begin this procedure, use 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.

"DESIRED SPEED" Potentiometer (if equipped)

The ECM provides 5.0 ± 0.5 VDC to the "DESIRED SPEED" potentiometer (if equipped).

A 262-3 diagnostic code is activated if both of these conditions occur:

• The desired speed signal wire is shorted to a voltage source that is greater than +5 volts.

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

A 262-4 diagnostic code is 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.

Illustration 1 is the schematic diagram for the operating voltage to the sensors. If the optional Auxiliary Sensing Module is not installed, the air inlet pressure sensor is connected to the ECM.

Illustration 1	g01325468

Test Step 1. Inspect the Electrical Connectors and Wiring

1. Remove the electrical power from the engine.

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

2. Thoroughly inspect the following connectors:

   • ECM connectors

   • Connectors on the terminal box

3. Check the torque of the allen head screws for the ECM connectors.

4. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuits for the sensors.

5. Check the harness and wiring for corrosion, for abrasion and for pinch points from each sensor to the 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. If you are troubleshooting a problem with the 5 volt supply for the ECM, proceed to Test Step 2. Otherwise, proceed to Test Step 4.

• 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 the Analog Speed Circuit

1. Rotate the "DESIRED SPEED" potentiometer (if equipped) clockwise to the maximum speed position.

Expected Result:

The 262-3 code or the 262-4 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 3.

Test Step 3. Check the Wiring for the "DESIRED SPEED" Potentiometer

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

2. Disconnect the P1 connector from the ECM.

3. Measure the resistance between terminals P1-16 and P1-69.

Expected Result:

The resistance is greater than five Ohms.

Results:

• Yes - The resistance is greater than five 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. Connect the wiring to the "DESIRED SPEED" potentiometer. Be sure to connect the wires to the appropriate terminals.

  3. Connect the P1 connector to the ECM.

  4. Verify that the original problem is resolved.

  STOP

• Not OK - The resistance is less than five Ohms. There is a problem with the wiring for the "DESIRED SPEED" potentiometer. The problem could be between the P1 connector and the J6 connector. Alternatively, the problem could be in the P6 connector or the wiring that is connected to the P6 connector.

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

  STOP

Test Step 4. Check the Sensors

1. Refer to Illustration 1. Disconnect the sensors that apply to the ECM and the power supply that has the diagnostic code.

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

2. Observe the "Active Diagnostic" screen on Cat ET.

Expected Result:

The active diagnostic code for the power supply is deactivated when a particular sensor is disconnected.

Results:

• Yes - The active diagnostic code for the power supply is deactivated when a particular sensor is disconnected. The sensor has a short circuit.

  Repair: Connect the suspect sensor. Verify that the diagnostic code for the power supply returns. Replace the sensor.

  STOP

• No - The original diagnostic code is still active while all of the sensors are disconnected. Do not connect the sensors. Proceed to Test Step 5.

Test Step 5. Check the Wiring

1. Refer to Table 1. Identify the ECM with the diagnostic code. Select the diagnostic code in order to determine the connector terminals for the power supply.
   Show/hide table

   Table 1

   Connectors and Terminals That Relate to Diagnostic Codes
   ECM	Diagnostic Code	Connector and Terminals
   Auxiliary Sensing Module (ASM)	262-3 262-4	P3-2
   	145-3 145-4	P3-43
   ECM	262-3 262-4	P1-2 and P1-18
   	41-3 41-4	P2-56 and P2-57
   	145-3 145-4	P1-43

2. Use a 151-6320 Wire Removal Tool to remove the appropriate terminal or terminals from the connector. This disconnects the wiring from the ECM.

Expected Result:

The diagnostic code is cleared when a particular terminal is disconnected from the ECM connector.

Results:

• Yes - The diagnostic code is cleared when a particular terminal is disconnected from the ECM connector. There is a problem with the wiring between the ECM and the sensors.

  Repair: Make the necessary repairs. Replace parts, if necessary.

  Connect all of the sensors. Restore all wiring to the original configuration.

  STOP

• No - The diagnostic code remains after all of the applicable terminals are removed from the ECM connector. There is a problem with the ECM.

  Repair: Connect all of the sensors. Restore all wiring to the original configuration.

  Replace the ECM. Refer to Troubleshooting, "ECM - Replace".

  STOP