3126B Engine for Caterpillar Built Machines Caterpillar

The Electronic Control Module (ECM) supplies a regulated voltage of 5.0 ± 0.5 VDC to the following sensors:

• Atmospheric pressure sensor

• Engine oil pressure sensor

• Fuel pressure sensor

• Fan drive pressure sensor

• Injection actuation pressure sensor

• Turbocharger outlet pressure sensor

Illustration 1	g00904082
Schematic

Test Step 1. Inspect Electrical Connectors and Wiring

Illustration 2	g00904083
ECM connectors (wire side)

1. Thoroughly inspect the J1/P1 ECM connector, the J2/P2 ECM connector, and the connectors for each pressure sensor.

   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 connectors that are associated with the +5 V sensor supply.

   Refer to Illustration 2.

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. Check for Active Diagnostic Codes

1. Connect the Caterpillar Electronic Technician (Cat ET) to the service tool connector.

2. Turn the keyswitch to the ON position.

3. Monitor the active diagnostic code screen on 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:

Note 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:

• 262-03 Active - Proceed to Test Step 3.

• 262-04 Active - Proceed to Test Step 4.

• 262-03 or 262-04 Logged ONLY - Proceed to Test Step 6.

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

Test Step 3. Short the Output at the ECM

1. Turn the keyswitch to the OFF position.

2. Remove the J844-GY wire from P1:2 (Engine Pressure Sensor +5V), the G828-WH wire from P2:2 (Engine Pressure Sensor +5V), and the G826-BR from P2:41 (Engine Pressure Sensor +5V).

3. Install a jumper wire between P1:2 (Engine Pressure Sensor +5V) and the ECM ground strap. Install another jumper wire between P2:2 (Engine Pressure Sensor +5V) and the ECM ground strap. Install another jumper wire between P2:41 (Engine Pressure Sensor +5V)and the ECM ground strap.

4. Turn the keyswitch to the ON position.

5. Check for active diagnostic codes on Cat ET.

Expected Result:

The 262-03 5 Volt Sensor Supply short to +batt should change to a 262-04 5 Volt Sensor Supply short to ground when the jumper wire is installed.

Results:

• OK - The ECM is responding correctly. Proceed to Test Step 5.

• Not OK - The ECM is not responding correctly.

  Repair: Verify your results before replacing the ECM. Refer to Troubleshooting, "Replacing the ECM" before you replace the ECM.

  Stop.

Test Step 4. Open the Output at the ECM

1. Turn the keyswitch to the OFF position.

2. Remove the J844-GY wire from P1:2 (Engine Pressure Sensor +5V), the G828-WH wire from P2:2 (Engine Pressure Sensor +5V), and the G826-BR from P2:41 (Engine Pressure Sensor +5V).

3. Turn the keyswitch to the ON position.

4. Check for active diagnostic codes on Cat ET.

5. Reinstall the wires that were removed from the ECM connectors.

Expected Result:

The 262-04 5 Volt Sensor Supply short to ground should no longer be active when the wires are removed from the ECM connectors.

Results:

• OK - The ECM is responding correctly. Proceed to Test Step 5.

• Not OK - The ECM is not responding correctly.

  Repair: Verify your results before replacing the ECM. Refer to Troubleshooting, "Replacing the ECM" before you replace the ECM.

  Stop.

Test Step 5. Disconnect the +5 V Pressure Sensors while You Monitor the Active Diagnostic Codes

1. Connect Cat ET to the service tool connector.

2. Turn the keyswitch to the ON position.

3. 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

4. Disconnect the following sensors one at a time:
   • Fan drive pressure sensor

   • Fuel pressure sensor J208/P208

   • Turbocharger outlet pressure sensor J200/P200

   • Engine oil pressure sensor J201/P201

   • Atmospheric pressure sensor J203/P203

   • Injection actuation pressure sensor J204/P204

5. Wait for 30 seconds after each pressure sensor is disconnected while you monitor the active diagnostics screen on Cat ET in order to verify that the disconnection of a specific sensor deactivates the +5 V 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 V diagnostic codes are no longer active. This is normal. Clear these diagnostic codes after this test step is completed.

Expected Result:

The original +5 V diagnostic code remains active.

Results:

• OK - The +5 V diagnostic code is still active. The harness is the cause of the problem. Leave the sensors disconnected. Proceed to Test Step 6.

• Not OK - The +5 V 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 6. Check the Wiring Harness for Shorts

Illustration 3	g00904084
ECM connectors (ECM side)

1. Turn the keyswitch to the OFF position.

2. Disconnect the J1/P1 and J2/P2 ECM connectors. Verify that all of the following +5 V engine pressure sensors that are attached to the ECM connectors are disconnected:
   • Fan drive pressure sensor

   • Turbocharger outlet pressure sensor J200/P200

   • Engine oil pressure sensor J201/P201

   • Atmospheric pressure sensor J203/P203

   • Injection actuation pressure sensor J204/P204

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

3. Measure the resistance from the ECM engine harness connector P2:2 (Engine Pressure Sensor +5V) to each of the following terminals:
   • P2:3

   • P2:14

   • P2:16

   • P2:24

   • P2:27

   • P2:40

4. Measure the resistance from the ECM engine harness connector P2:2 (Engine Pressure Sensor +5V) to each of the following terminals:
   • P2:3

   • P2:14

   • P2:16

   • P2:24

   • P2:27

   • P2:40

5. Measure the resistance from the ECM machine harness connector P1:2 (Engine Pressure Sensor +5V) to each of the following terminals:
   • P1:3

   • P1:15

Expected Result:

Each resistance measurement is more than 20 Ohms.

Results:

• OK - The +5 V 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: Repair the circuit. Clear all logged diagnostic codes. Verify that the repair eliminates the problem.

  Stop.