C27 Generator Set Engines Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the sensors. Also use this test procedure if any one of the diagnostic codes in Table 1 is active or easily repeated.

The supply voltage is routed to terminal 1 of each sensor connector. The sensor return is routed to terminal 2 of each sensor connector. For the pressure sensors, the sensor signal is routed to terminal 3 of each sensor connector.

The ECM provides short circuit protection for the internal power supply. A short circuit to the battery will not damage the internal power supply.

Diagnostic Testing using Caterpillar Electronic Technician (ET)

Wiggle Test - The wiggle test allows the technician to monitor the status of the signals from the sensors. For additional information regarding the wiggle test, refer to the documentation that accompanies the Cat ET software.

Illustration 1	g02175025
Schematic for the active sensors

Illustration 2	g02175152
Terminal locations at the P2 ECM connector for the analog sensors (P2-15) Intake manifold pressure sensor (P2-27) Fuel pressure sensor (filtered fuel pressure) (P2-28) Engine oil pressure sensor (P2-30) Analog return (P2-33) Crankcase pressure sensor (P2-40) NRS differential pressure sensor (P2-72) Analog supply (P2-74) NRS absolute pressure sensor (P2-78) Atmospheric pressure sensor (P2-81) Analog supply (P2-83) Analog return

Test Step 1. Check for Diagnostic Codes

1. Connect Cat ET to the service tool connector. Establish a connection with the engine ECM.

2. Turn the keyswitch to the ON position.

3. Look for the following codes that are active or logged:

   • -3

   • -4

   • -10

   • -21

Results:

• Active -3 Code - A -3 diagnostic code is active. Proceed to Test Step 2.

• Active -4 code - A -4 diagnostic code is active. Proceed to Test Step 3.

• Active -21 Code - A -21 diagnostic code is active.

  Repair: The -21 diagnostic code indicates that the sensor is not receiving the correct supply voltage. Refer to Troubleshooting, "Sensor Supply - Test" for information that is related to troubleshooting the supply circuit for the suspect sensor.

  STOP

Test Step 2. Create a Short at the Sensor Connector

1. Use a test lamp in order to create a short between terminal 3 (signal) and terminal 2 (return) at the sensor connector.

2. Turn the keyswitch to the ON position.

3. Monitor the diagnostic codes on Cat ET. Check for an active -4 diagnostic code for the suspect sensor.

4. Turn the keyswitch to the OFF position.

Results:

• Active -4 - A -4 diagnostic code became active after creating the short at the sensor connector.

  Repair: The wiring is OK. Replace the sensor.

  Verify that the problem is resolved.

  STOP

• Active -3 - The -3 diagnostic code remains active for the suspect sensor. Proceed to Test Step 4.

Test Step 3. Create an Open at the Suspect Sensor Connector

1. Turn the keyswitch to the OFF position.

2. Disconnect the sensor connector of the suspect sensor with the active -4 diagnostic code.

3. Turn the keyswitch to the ON position.

4. Monitor the diagnostic codes on Cat ET. Check for an active -3 diagnostic code for the suspect sensor.

5. Turn the keyswitch to the OFF position.

Results:

• Active -3 - A -3 diagnostic code became active after disconnecting the sensor.

  Repair: The wiring is OK. Replace the sensor.

  Verify that the problem is resolved.

  STOP

• Active -4 - The -4 diagnostic code remains active for the suspect sensor. Proceed to Test Step 4.

Test Step 4. Check the 5 V Supply Voltage at the Sensor Connector

1. Turn the keyswitch to the ON position.

2. Measure the voltage between pin 1 (analog supply) and pin 2 (analog return).

Expected Result:

The supply voltage at the sensor connector is 5.0 ± 0.2 VDC.

Results:

• OK - The supply voltage is approximately 5.0 ± 0.2 VDC. Connect the sensor and then proceed to Test Step 5.

• Not OK - The supply voltage is not approximately 5.0 ± 0.2 VDC.

  Repair: There is a short circuit to battery voltage in the wiring harness. Repair the wiring or replace the harness.

  Verify that the problem is resolved.

  STOP

Test Step 5. Perform the Wiggle Test on the Suspect Harness

Carefully following this procedure is the best way to identify the root cause of an intermittent problem.

1. Turn the keyswitch to the ON position.

2. Use Cat ET to start the wiggle test.

3. Slowly wiggle the wiring and the connectors between each of the ECM connectors and the sensor. Pay particular attention to the wiring near each connector. Be sure to wiggle all of the wiring.

   As you wiggle the wiring look for these problems.

   • Loose connectors or damaged connectors

   • Moisture on the connectors or the wiring

   • Damage that is caused by excessive heat

   • Damage that is caused by chafing

   • Improper routing of wiring

   • Damaged insulation

Expected Result:

Each segment of the wiring harness passed the wiggle test.

Results:

• - The wiring passed the wiggle test.

  Repair: There may be an intermittent problem in the harness or in a connector. Recheck each segment of the wiring harness. Refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to the inspection of wiring and connectors.

  If the wiring appears to be OK, perform the following procedure:

  1. Turn the keyswitch to the OFF position.

  1. Disconnect the connectors. Carefully inspect the terminals for proper installation. Ensure that each terminal in the connector is clean and dry.

  2. Insert a pin into each socket. Verify that each socket grips the pin firmly. Repair any problems.

  3. Connect all connectors.

  4. Verify that the problem is resolved.

  5. Return the unit to service.

  STOP

• Not OK - The wiggle test identified a problem in the harness.

  Repair: There is a problem with the wiring. Repair the wiring or replace the wiring.

  Verify that the problem is resolved.

  STOP