C18 Marine Engines Caterpillar

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

System Operation

The ECM supplies a regulated voltage of 5.0 ± 0.2 VDC to the following sensors:

• Engine oil pressure sensor

• Fuel pressure sensor

• Intake manifold pressure sensor

• Transmission oil pressure sensor

• Transmission oil temperature sensor

The ECM supplies a regulated voltage of 8.0 ± 0.4 VDC to the following sensors:

• Coolant level sensor

• Exhaust temperature sensor

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

If a -10 code is logged, this indicates that the 5 volt supply is not available at the sensor connector. During normal engine operation, each of the signals from the pressure sensors fluctuate slightly. When the 5 volt supply becomes unavailable at the pressure sensor connector, the signal from that sensor floats to a midrange value. The signal will not fluctuate. If the signal from the sensor remains abnormally steady for more than 30 seconds, the ECM will activate this code.

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 3 diagnostic codes are active, it is possible that a sensor has been damaged. Repair the sensor supply and check for any active sensor diagnostic codes in order to determine if a sensor has failed.

Illustration 1	g01373855
Schematic for the sensor supply circuit

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove electrical power from the ECM. Turn the keyswitch to the OFF position.
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   Illustration 2	g01373903
   Locations of the components for the sensor supply (typical left side engine view) (1) Coolant level sensor (2) Intake manifold pressure sensor (3) Fuel pressure sensor (4) Engine oil pressure sensor (5) J2/P2 ECM connectors

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   Illustration 3	g01373963
   Locations of the connectors for the analog sensors and the digital sensors (typical rear engine view) (6) Connector for the transmission pressure sensor (7) Connector for the exhaust temperature sensor (8) Connector for the transmission temperature sensor

2. Thoroughly inspect the connectors for sensors (1 through 4). Also, thoroughly inspect connectors (5 through 8).

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

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   Illustration 4	g01374012
   Terminal locations at the P2 ECM connector for the sensor supply (P2-17) Analog return (P2-29) Digital sensor supply (P2-54) Analog return (P2-72) Analog sensor supply (P2-80) Analog sensor supply (P2-81) Digital sensor supply (P2-92) Digital return (P2-93) Digital return

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   Illustration 5	g01159881
   Terminal locations at the sensor connector for the sensor supply (Terminal A) Sensor supply (Terminal B) Sensor return (Terminal C) Sensor signal

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 completely 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 completely coupled.

  Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check for Active Diagnostic Codes

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 active diagnostic codes. Look for the following diagnostic codes:

   • 41-3

   • 41-4

   • 100-10

   • 262-3

   • 262-4

   • 1785-10

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

Expected Result:

No diagnostic codes are active.

Results:

• OK - No diagnostic code is active.

  Repair: The problem is no longer present. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The 100-10 or 1785-10 diagnostic code is logged at this time. The analog supply is not reaching the sensor. Proceed to Test Step 3.

• Not OK - A 262-3 or 262-4 diagnostic code is active at this time. There is a problem with the sensor supply for the analog sensors. Proceed to Test Step 4.

• Not OK - A 41-3 or 41-4 diagnostic code is active at this time. There is a problem with the sensor supply for the digital sensors. Proceed to Test Step 6.

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

1. Disconnect the harness connectors for the 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 A and B at the connector.

4. Remove the electrical power from the ECM.

5. Connect all of the sensors.

Expected Result:

The voltage measurement is 5.0 ± 0.2 VDC.

Results:

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

  Repair: The analog sensor 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. Use Cat ET to check for diagnostic codes that have become active or logged.
  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 - The 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 Monitor the Active Diagnostic Codes

1. Ensure that the ECM is receiving electrical power.

2. Monitor the active diagnostic code screen on Cat ET while you disconnect each 5 Volt sensor at the sensor connector. Check for an active 262-3 code or an active 262-4 code.

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

3. Disconnect the following sensors one at a time:

   • Engine oil pressure sensor

   • Fuel pressure sensor

   • Intake manifold pressure sensor

   • Transmission oil pressure sensor

   • Transmission oil temperature sensor

4. Remove electrical power from the ECM.

Expected Result:

The diagnostic code deactivates when a particular sensor is disconnected.

Results:

• OK - The diagnostic code deactivates when a particular sensor is disconnected.

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

  STOP

• Not OK - The diagnostic code remains active after the sensors are disconnected. Leave the sensors disconnected. The sensors are not the cause of the diagnostic code. Proceed to Test Step 5.

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

1. Disconnect the J2/P2 ECM connector.

2. Fabricate four jumper wires that are long enough to be used to create a test circuit at the ECM connector. Crimp connector sockets to one end of each of the jumper wires.

3. Remove the wires from terminal locations P2-72 (analog sensor supply) and P2-17 (analog return). Install a jumper wire into each of these terminal locations.

4. Remove the wires from terminal locations P2-80 (analog sensor supply) and P2-54 (analog return). Install a jumper wire into each of these terminal locations.

5. Connect the J2/P2 ECM connector.

6. Restore electrical power to the engine ECM.

7. Measure the voltage between the jumper wire in P2-72 (analog sensor supply) and the jumper wire in P1-17 (analog return).

8. Measure the voltage between the jumper wire in P2-80 (analog sensor supply) and the jumper wire in P1-54 (analog return).

9. Remove electrical power from the ECM.

Expected Result:

Each voltage measurement is 5.0 ± 0.2 VDC.

Results:

• OK - The voltage measurement is 5.0 ± 0.2 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 circuit in the supply wire that is in the harness. Repair the supply wire.

  STOP

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

  Repair: The ECM is not generating the correct supply voltage. There is a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "ECM - Replace".

  STOP

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

1. Monitor the active diagnostic code screen on Cat ET while you disconnect each of the digital sensors at the sensor connector. Check for an active 41-3 code or an active 41-4 code.

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

2. Disconnect the following sensors one at a time:

   • Coolant level sensor

   • Exhaust temperature sensor

3. Remove electrical power from the ECM.

Expected Result:

The diagnostic code deactivates when the coolant level sensor is disconnected.

Results:

• OK - The 41-3 or 41-4 diagnostic code deactivates when one of the digital sensors is disconnected.

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

  STOP

• Not OK - The 41-3 or 41-4 diagnostic code remains active after one of the digital sensors is disconnected. A sensor is not the cause of the diagnostic code. Leave the sensors disconnected. Proceed to Test Step 7.

Test Step 7. Check the Digital Supply Voltage at the ECM

1. Disconnect the J2/P2 ECM connector.

2. Fabricate four jumper wires that are long enough to be used to create a test circuit at the ECM connectors. Crimp connector sockets to one end of each of the jumper wires.

3. Remove the wires from terminal locations P2-29 (digital sensor supply) and P1-92 (digital return). Install a jumper wire into each of these terminal locations.

4. Remove the wires from terminal locations P2-81 (digital sensor supply) and P1-93 (digital return). Install a jumper wire into each of these terminal locations.

5. Connect the J2/P2 ECM connector.

6. Restore electrical power to the engine ECM.

7. Measure the voltage between the jumper wire in P1-29 (digital sensor supply) and P1-92 (digital return).

8. Measure the voltage between the jumper wire in P1-81 (digital sensor supply) and P1-93 (digital return).

9. Remove electrical power from the ECM. Restore all 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 circuit in the supply wire 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 generating the correct supply voltage. There is a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "ECM - Replace".

  STOP