3176C Engine for Caterpillar Built Machines Caterpillar

Use this procedure under the following situation:

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

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

• 262-04 5 Volt Sensor Supply short to ground

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

The following background information is related to this procedure:

The Electronic Control Module (ECM) supplies regulated +5 VDC to the following sensors:

• J200/P200 Turbocharger outlet pressure sensor

• J203/P203 Atmospheric pressure sensor

• J201/P201 Engine oil pressure sensor

• J208/P208 Fuel pressure sensor

The +5 VDC is supplied from the ECM through ECM engine harness connector J2/P2 terminal 2 to terminal "A" of each pressure sensor connector. The supply voltage is 5.0 ± 0.5 VDC.

The +5 volt short circuit diagnostic code is probably caused by a short circuit or an open circuit in the harness. The next probable cause is a sensor and the least probable cause is the ECM.

Illustration 1	g00884119
Locations of +5 volt sensors (typical side view)

Illustration 2	g00700489
Locations of +5 volt sensors (typical top view)

Illustration 3	g00890843
Schematic for +5 volt sensors

Test Step 1. Inspect Electrical Connectors And Wiring.

Illustration 4	g00796051
Terminal locations for ECM

Illustration 5	g00897279
Terminal locations

1. Thoroughly inspect the following connections:
   • ECM engine harness connector J2/P2

   • ECM machine harness connector J1/P1

   • Turbocharger outlet pressure sensor J200/P200

   • Engine oil pressure sensor J201/P201

   • Atmospheric pressure sensor J203/P203

   • Fuel pressure sensor J208/P208

   Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

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 sensor supply:
   • P2:2 Engine Pressure Sensor +5 V (G828-WH)

   • P1:2 Engine Pressure Sensor +5 V (GL730-OR)

   • P2:3 Engine Pressure Sensor Common (G829-GN)

   • P1:3 Engine Pressure Sensor Common (993-BN)

   Refer to Illustration 4.

3. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

4. Check the harness and wiring for abrasion and pinch points from the sensors back to the ECM.

Expected Result:

All connectors, pins and sockets should be completely coupled and/or inserted and the harness and wiring should be free of corrosion, abrasion or pinch points.

Results:

• OK - Proceed to Test Step 2.

• Not OK -

  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. Connect the Caterpillar Electronic Technician (Cat ET) and Check for Active Diagnostic Codes

1. Connect Cat ET to the data link connector.

2. Turn the keyswitch to the ON position while the engine is OFF.

3. Monitor the active diagnostic code screen of Cat ET. Check and record any active diagnostic codes.

   Note: Wait at least 15 seconds in order for the diagnostic codes to become active.

Expected Result:

Select the condition of the following codes:

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

• 262-04 5 Volt Sensor Supply short to ground

Results:

• Active - Proceed to Test Step 3.

• Logged ONLY - Proceed to Test Step 5.

• Not Active or Logged - The +5 volt supply is operating correctly at this time. Stop.

Test Step 3. Disconnect The ECM Engine Harness Connector From The ECM.

1. Turn the keyswitch to the OFF position while the engine is OFF.

2. Disconnect ECM engine harness connector J2/P2.

3. Turn the keyswitch to the ON position while the engine is OFF.

4. Access the active diagnostic code screen on Cat ET. Check for one of the following active diagnostic codes:
   • 262-03 5 Volt Sensor Supply short to +batt

   • 262-04 5 Volt Sensor Supply short to ground

   Note: When ECM engine harness connector J2/P2 is disconnected and the keyswitch is in the ON position, open circuit diagnostic codes will be "Active" or "Logged" for all of the engine sensors. This is normal.

Expected Result:

The +5 volt diagnostic code is active when the ECM engine harness connector is disconnected.

Results:

• Yes - The +5 volt diagnostic code is active when the ECM engine harness connector is disconnected.

  Repair: Temporarily connect a test ECM to ECM machine harness connector J1/P1. Recheck for a +5 volt diagnostic code. If a +5 volt diagnostic code is not active, the original ECM is faulty. Reconnect the original ECM and check the +5 volt diagnostic codes. If a +5 volt diagnostic code becomes active, replace the ECM.

  Stop.

• No - The +5 volt sensor diagnostic code is no longer active when the harness is disconnected. Either the harness or a sensor that is attached to the harness is causing the problem. Reconnect the ECM engine harness connector. Proceed to Test Step 4.

Test Step 4. Disconnect The +5 Volt Sensors While Active Diagnostic Codes Are Being Monitored.

1. Turn the keyswitch to the ON position while the engine is OFF.

2. Access the active diagnostic code screen on Cat ET. Verify that one of the following diagnostic codes is active:
   • 262-03 5 Volt Sensor Supply short to +batt

   • 262-04 5 Volt Sensor Supply short to ground

3. Disconnect the following sensors one at a time:
   • Turbocharger outlet pressure sensor J200/P200

   • Engine oil pressure sensor J201/P201

   • Atmospheric pressure sensor J203/P203

   • Fuel pressure sensor J208/P208

4. Wait for 30 seconds after each pressure sensor is disconnected while Cat ET is being monitored in order to verify that the disconnection of a specific sensor deactivates the +5 volt diagnostic code.

   Note: When the sensors are disconnected and the keyswitch is in the ON position, open circuit diagnostic codes will be active or logged when the +5 volt diagnostic codes are no longer active. This is normal. Clear these diagnostic codes after this test step is completed.

Expected Result:

The original +5 volt diagnostic code remains active.

Results:

• Yes - The +5 volt diagnostic code is still active. The harness is the cause of the problem. Leave the sensors disconnected. Proceed to Test Step 5.

• No - The +5 volt diagnostic code is not active when a specific sensor is disconnected.

  Repair: Reconnect the sensor that is suspected of causing the problem. If the problem returns after the reconnection of the sensor, disconnect the sensor. If the problem disappears after the disconnection of the sensor, replace the sensor.Clear all diagnostic codes. Verify that the repair eliminates the problem.

  Stop.

Test Step 5. Check the Engine Harness.

Illustration 6	g00796051
Connectors P1 and P2

Illustration 7	g00897279
Terminal locations

1. Turn the keyswitch to the OFF position while the engine is OFF.

2. Disconnect ECM connector J2/P2 and ECM J1/P1. Verify that all of the +5 volt engine pressure sensors that are attached to the ECM connectors are disconnected.
   • Turbocharger outlet pressure sensor J200/P200

   • Engine oil pressure sensor J201/P201

   • Atmospheric pressure sensor J203/P203

   • Fuel pressure sensor J208/P208

3. Set a multimeter in order to measure the resistance on the range that is close to 20 Ohms, but not less than 20 Ohms.

   1. Measure the resistance from the ECM engine harness connector P2:2 (+5 Volt Engine Pressure Sensor) to each of the following terminals:
      • P2:14

      • P2:24

      • P2:40

      • P2:3

      Refer to Illustration 6.

   2. Measure the resistance from the ECM machine harness connector P1:2 (+5 Volt Engine Pressure Sensor) to each of the following terminals:
      • P1:16

      • P1:3

   3. Wiggle the harness during the measurement in order to reveal any intermittent short condition.

Expected Result:

Each resistance measurement is more than 20 Ohms.

Results:

• OK - The +5 volt line is not shorted in the engine harness. Ensure that the engine harness is connected to the ECM and that all of the sensors are reconnected. There does not appear to be a problem at this time. Clear all diagnostic codes. Continue to troubleshoot until the original condition is resolved. Stop.

• Not OK -

  Repair: Replace the engine harness. Clear all logged diagnostic codes. Verify that the repair eliminates the problem.

  Stop.