865835T02 Mercruiser ECM, Engine Control Module

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Schematic for the Cat Data Link (typical example)
Test Step 1. Inspect the Electrical Connectors and the Wiring
Remove electrical power from the engine ECM.
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J1/P1 ECM connectors (typical left side engine view)
Thoroughly inspect the J1/P1 ECM connectors. Inspect all of the connectors to other modules that are on the Cat Data Link. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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Terminals at the P1 ECM connector for the Cat Data Link
(P1-8) Cat Data Link +
(P1-9) Cat Data Link −
Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit.
Check the allen head screw for each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
Check the harness and the wiring for abrasion and for pinch points. Expected Result:All of the 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 - The connectors and/or wiring are 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.STOPTest Step 2. Check for Shorts in the Harness
Disconnect the J1/P1 ECM connectors.
Disconnect all control modules from the Cat Data Link.
Disconnect Cat ET from the service tool connector . Note: Wiggle the harness during the following measurements in order to reveal an intermittent condition.
Measure the resistance from P1-8 to every terminal on the P1 ECM connector.
Measure the resistance from P1-8 to the chassis ground.
Measure the resistance from P1-9 to every terminal on the P1 ECM connector.
Measure the resistance from P1-9 to the chassis ground. Expected Result:Each check of the resistance indicates an open circuit.Results:
OK - Each check of the resistance indicates an open circuit. There does not appear to be a short in the harness. Proceed to Test Step 3.
Not OK - At least one check of the resistance does not indicate an open circuit.Repair: There is a short circuit in one of the harnesses. There may be a problem with a connector. Repair the wiring and/or the connector. Replace parts, if necessary. Verify that the problem is resolved.STOPTest Step 3. Check for an Open in the Harness
Fabricate a jumper wire that is long enough to create a short across two terminals at the service tool connector. Crimp connector sockets to each end of the jumper wire.
Install the jumper wire between terminals D and E at the service tool connector.
Measure the resistance between P1-8 and P1-9.
Measure the resistance at the connectors of all of the other control modules. Expected Result:The resistance is less than 5 Ohms for each measurement.Results:
OK - The resistance is less than 5 Ohms for each measurement.Repair: The Cat Data Link does not have an open in the harness. The problem seems to be resolved. There may be an intermittent electrical problem in the wiring harness. There may be a problem with a connector. Inspect the harness and the connectors carefully. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect".STOP
Not OK - The resistance is greater than 5 Ohms for one or more of the measurements. There is excessive resistance or an open circuit in the harness or the connectors.Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Verify that the problem is resolved.STOP