879194T85 Mercruiser ECM, Engine Control Module

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Schematic for the engine temperature sensors
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P2 ECM connector (P2-13) Engine coolant temperature (P2-30) Common for the engine temperature sensors (P2-56) Intake manifold air temperature (P2-62) Fuel temperature
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Typical C11 and C13 sensor locations (1) Engine coolant temperature sensor (2) Fuel temperature sensor (3) Intake manifold air temperature sensor
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Typical C15 and C18 sensor locations (4) Engine coolant temperature sensor (5) Fuel temperature sensor (6) Intake manifold air temperature sensorTest Step 1. Inspect Electrical Connectors and Wiring
Turn the keyswitch to the OFF position.
Thoroughly inspect the J1/P1 ECM connector and the J2/P2 ECM connector. Thoroughly inspect the connectors for each analog sensor.Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the sensor connectors that are associated with the active diagnostic code.
Check the ECM connector (allen head screw) for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Check the harness and wiring for abrasions and for pinch points from the sensors back to the ECM.Expected Result:All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.Results:
OK - The harness and wiring are OK. Proceed to Test Step 2.
Not OK - There is a problem in 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.STOPTest Step 2. Check for "Active" or "Logged" Diagnostic Codes
Connect Caterpillar Electronic Technician (ET) to the service tool connector.
Restore electrical power to the ECM.
Monitor the diagnostic codes on Cat ET. Check and record any diagnostic codes.Note: Wait at least 30 seconds in order for the diagnostic codes to become active.
Determine if a diagnostic code has occurred several times.Note: A diagnostic code that is logged several times is an indication of an intermittent problem. Most intermittent problems are the result of a bad connection between a socket and a pin in a connector or a bad connection between a wire and a terminal. The problem may be caused by moisture, corrosion, or wear.
Determine if the problem is active and related to one of the following diagnostic codes:
-3
-4Expected Result:A diagnostic code is not active.Results:
OK - A diagnostic code is not active.Repair: The problem may be intermittent. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect".STOP
Not OK - An active -3 diagnostic code is present. Proceed to Test Step 3.
Not OK - An active -4 diagnostic code is present. Proceed to Test Step 5.Test Step 3. Check for a Short to the +Battery at the Sensor Connector
Measure the voltage on the harness side of the sensor connector between pin 1 and pin 2 for the suspect sensor(s).Expected Result:The voltage is less than battery voltage.Results:
OK - The voltage is less than battery voltage. Proceed to Test Step 4.
Not OK - The voltage is equal to battery voltage.Repair: There is a short in the harness to the +Battery. Repair the wiring.STOPTest Step 4. Create a Short at the Sensor Connector
Remove electrical power from the ECM.
Disconnect the suspect sensor.
Use a wire jumper in order to create a short between terminal 1 (signal) and terminal 2 (sensor return) at the sensor connector.
Restore electrical power to the ECM.
Monitor the diagnostic codes on Cat ET. Check for an active -4 diagnostic code for the suspect sensor.Note: Wait at least 30 seconds in order for the diagnostic codes to become active.
Remove electrical power from the ECM.Expected Result:A -4 diagnostic code is now active for the suspect sensor(s).Results:
OK - A -3 diagnostic code was active before creating the short at the sensor connector. A -4 diagnostic code became active after creating the short at the sensor connector. The harness and the ECM are OK. There may be a problem with the sensor.Repair: Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Verify that there are no active diagnostic codes for the sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes.STOP
Not OK - A -3 diagnostic code is still active for the suspect sensor(s). The problem may be in the harness or with the ECM. Proceed to Test Step 6.Test Step 5. Create an Open at the Suspect Sensor Connector
Remove electrical power from the ECM.
Disconnect the sensor connector of the suspect sensor(s) with the active -4 diagnostic code.
Restore electrical power to the ECM.
Monitor the diagnostic codes on Cat ET. Check for an active -3 diagnostic code for the suspect sensor.Note: Wait at least 30 seconds in order for the diagnostic codes to become active.
Remove electrical power from the ECM.Expected Result:A -3 diagnostic code is now active for the suspect sensor(s).Results:
OK - A -4 diagnostic code was active before disconnecting the sensor. A -3 diagnostic code