C27 and C32 Tier 4 Engines Caterpillar

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

System Operation

The Electronic Control Module (ECM) supplies a regulated voltage of 5.0 ± 0.2 VDC to the following sensors:

• Engine oil pressure sensor

• Barometric pressure sensor

• Crankcase pressure sensor

• Intake manifold pressure sensor #1 (left-hand)

• Intake manifold pressure sensor #2 (right-hand)

• NRS absolute pressure sensor

• Fuel pressure sensor before the filter

• Fuel pressure sensor after the filter

• NRS delta pressure sensor

• Auxiliary #1 Pressure Sensor

The ECM supplies a regulated voltage of 8.0 ± 0.4 VDC to each of the throttle position sensors.

The supply voltage for the sensors is routed from the ECM to terminal 1 of each sensor connector. The sensor return for the sensors is routed from the ECM to terminal 2 of each sensor connector.

The -21 code becomes active when the ECM determines that the 5 V supply is missing at the pressure sensor. The ECM sets the value of the suspect sensor to the default value.

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

Note: The sensors are not protected from overvoltage. A short from the supply line to the +Battery may damage the sensors. If any of the three diagnostic codes are active, one of the sensors may be damaged. Repair the sensor supply and check for any active sensor diagnostic codes in order to determine if a sensor has been damaged.

Illustration 1	g03884993

Illustration 2	g02160270
Schematic for the 8 V sensors

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove the electrical power from the ECM.
   Show/hide table

   Illustration 3	g02138858
   Location of the ECM connectors (left side engine view) (1) J1/P1 ECM connectors (2) J2/P2 ECM connectors

2. Thoroughly inspect connectors (1) and (2). Inspect all of the connectors that are associated with the sensors.

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

   Show/hide table

   Illustration 4	g02138860
   Terminal locations at the P1 ECM connector for the analog sensor supply and the digital sensor supply (P1-2) Analog sensor supply (P1-3) Analog sensor return (P1-4) Digital sensor supply (P1-5) Digital sensor return

   Show/hide table

   Illustration 5	g03885108
   Terminal locations at the P2 ECM connector for the analog sensor supplies (P2-30) Analog sensor return (P2-72) Analog sensor supply (P2-80) Analog sensor supply (P2-81) Analog sensor supply (P2-83) Analog sensor return (P2-93) Analog sensor return

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connectors that are associated with the circuit.

4. Check the allen head screw for each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.

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

Expected Result:

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

Results:

• OK - The harness and connectors appear to be OK. Proceed to Test Step 2.

• Not OK - There is a problem with the connectors and/or wiring.

  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 coupled.

  Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check for Diagnostic Codes that are Active or Logged

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

2. Restore electrical power to the ECM.

3. Monitor the active diagnostic code screen on Cat ET. Check and record any diagnostic codes that are active or logged. Look for the following diagnostic codes:

   • 678-3

   • 678-4

   • 3358-21

   • 3509-3

   • 3509-4

   • 3510-3

   • 3510-4

   • 2131-4

   • 3563-21

   • 5422-21

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

4. Remove the electrical power from the ECM.

Expected Result:

No diagnostic codes are active or logged.

Results:

• OK - No diagnostic codes are active or logged.

  Repair: There does not appear to be an electrical problem with the sensor supply at this time. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• 678-3 or 678-4 Active or Logged - Either the 678-3 or 678-4 diagnostic code is active or logged at this time. There is an electrical problem with the digital sensor supply. Proceed to Test Step 6.

• 3358-21, 3563-21, or 5422-21 Logged - A -10 or -21 diagnostic code is logged at this time. The analog supply is not reaching the sensor or there is a problem with the sensor. Proceed to Test Step 3.

• 3510-3 or 3510-4 Active or Logged - Either the 3510-3 or 3510-4 diagnostic code is active or logged at this time. There is an electrical problem with the analog sensor supply. Proceed to Test Step 4.

Test Step 3. Check the Supply Voltage at the Sensor Connector

1. Disconnect the harness connectors for the following sensors:

   • Fuel pressure sensor (filtered fuel pressure)

   • NRS absolute pressure sensor

   • Intake manifold pressure sensor

2. Restore the electrical power to the ECM.

   Note: Be sure to wiggle the harness during the following measurements in order to reveal an intermittent condition.

3. Measure the voltage between terminals 1 and 2 at the appropriate sensor connector.

4. Remove the electrical power from the ECM.

5. Connect all of the sensors.

Expected Result:

Each voltage measurement is 5.0 ± 0.2 VDC.

Results:

• OK - Each voltage measurement is 5.0 ± 0.2 VDC.

  Repair: The analog supply is reaching the sensor connector. There may be a problem with the sensor. Perform the following procedure:

  1. Clear all diagnostic codes.

  2. Run the engine. Allow the engine to warm up. Check if the code has been logged again.
  If the code becomes active or logged, the sensor is faulty. Replace the sensor. Verify that the repair eliminates the original problem.

  If the code does not become active or logged, there may be an intermittent problem in the harness or in a connector. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct troubleshooting procedure.

  STOP

• Not OK - At least one voltage measurement is not 5.0 ± 0.2 VDC. There is a problem with the harness wiring or with the ECM. Proceed to Test Step 5.

Test Step 4. Disconnect the Analog Sensors While You Check for Active Diagnostic Codes

1. Restore the electrical power to the ECM.

2. Monitor the active diagnostic code screen on Cat ET while you disconnect each 5 V sensor at the sensor connector. Check for an active 3509-3, 3509-4, 3510-3, or 3510-4.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

   1. Disconnect the following sensors one at a time:

      • Engine oil pressure sensor

      • Barometric pressure sensor

      • Crankcase pressure sensor

      • Intake manifold pressure sensor LH

      • NRS absolute pressure sensor

      • Fuel pressure sensor after the filter

      • NRS delta pressure sensor

3. Remove the electrical power from the ECM. Restore the wiring to the original configuration.

Expected Result:

The diagnostic code deactivates when a particular sensor is disconnected.

Results:

• OK - The 3509-3, 3509-4, 3510-3, or 3510-4 diagnostic code deactivates when a particular sensor is disconnected.

  Repair: Connect the suspect sensor. If the code returns, replace the sensor. Connect all of the connectors. Verify that the problem is resolved.

  STOP

• Not OK - The 3509-3, 3509-4, 3510-3, or 3510-4 diagnostic code remains active after all of the sensors are disconnected. The sensors are not the cause of the diagnostic code. Leave the sensors disconnected. Proceed to Test Step 5.

Test Step 5. Check the 5 V Supply Voltages at the ECM

1. Disconnect the J2/P2 and J2/P2 ECM connectors.

2. Fabricate eight jumper wires that are long enough to be used to measure the supply voltage at the ECM connector. Crimp connector sockets to one end of each jumper wire.

3. Remove the wires from the following terminal locations:

   • P1-2 (analog sensor supply)

   • P1-3 (analog sensor return)

   • P2-30 (analog sensor return)

   • P2-72 (analog sensor supply)

   • P2-81 (analog sensor supply)

   • P2-83 (analog sensor return)

   Install a jumper wire into each of these terminal locations.

4. Connect the J2/P2 ECM connector.

   Note: Ensure that the loose ends of the jumper wires do not contact any ground source.

5. Restore electrical power to the engine ECM.

6. Measure the voltage between the jumper wires in the following terminal locations:

   • P1-2 and P1-3

   • P2-72 and P2-83

   • P2-81 and P2-30

7. Remove electrical power from the ECM. Restore the wiring to the original configuration.

Expected Result:

The voltage measurement is 5.0 ± 0.2 VDC.

Results:

• OK - The voltage measurement is 5.0 ± 0.2 VDC.

  Repair: The ECM is operating correctly. The supply wire that is in the harness is shorted to another wire in the harness or the supply wire is shorted to engine ground. There may be an open in wiring that is in the harness. Repair the harness.

  STOP

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

  Repair: The ECM is not producing the correct supply voltage. There may be a problem with the ECM. Before you consider replacing the ECM, consult with the Dealer Solution Network (DSN).

  STOP

Test Step 6. Disconnect the Digital Sensors while you Check for Active Diagnostic Codes

1. Restore the electrical power to the ECM.

2. Disconnect the throttle position sensor at the sensor.

3. Monitor the active diagnostic code screen on Cat ET while you disconnect the throttle position sensor at the sensor connector. Check for an active 678-3 code or an active 678-4 code.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

4. Remove electrical power from the ECM. Restore the wiring to the original configuration.

Expected Result:

The diagnostic code deactivates when the throttle position sensor is disconnected.

Results:

• OK - The 678-3 or 678-4 diagnostic code deactivates when the throttle position sensor is disconnected.

  Repair: Connect the suspect sensor. If the code returns, replace the sensor. Connect all of the connectors. Verify that the problem is resolved.

  STOP

• Not OK - The 678-3 or 678-4 diagnostic code remains active after the sensor is disconnected. Leave the sensor disconnected. The sensor is not the cause of the diagnostic code. Proceed to Test Step 7.

Test Step 7. Check the 8 V Supply Voltage at the ECM

1. Disconnect the J1/P1 ECM connector.

2. Fabricate two jumper wires that are long enough to be used to measure the supply voltage at the ECM connectors. Crimp connector sockets to one end of each jumper wire.

3. Remove the wires from terminal locations P1-4 (digital sensor supply) and P1-5 (digital return). Install a jumper wire into each of these terminal locations.

4. Connect the J1/P1 ECM connector.

5. Restore electrical power to the engine ECM.

6. Measure the voltage between the jumper wire in P1-4 (digital sensor supply) and P1-5 (sensor return).

7. Remove electrical power from the ECM. Restore the wiring to the original configuration.

Expected Result:

The voltage measurement is 8.0 ± 0.4 VDC.

Results:

• OK - The voltage measurement is 8.0 ± 0.4 VDC. The ECM is operating correctly.

  Repair: The supply wire is shorted to another wire in the harness or the supply wire is shorted to engine ground. There may be an open in the wiring that is in the harness. Repair the supply wire.

  STOP

• Not OK - The voltage measurement is not 8.0 ± 0.4 VDC.

  Repair: The ECM is not producing the correct supply voltage. There may be a problem with the ECM. Before you consider replacing the ECM, consult with the Dealer Solution Network (DSN).

  STOP