879172105 Mercruiser SENSOR

Illustration 1 g00713332
SchematicTest Step 1. Inspect Electrical Connectors and Wiring
Turn the keyswitch to the OFF/RESET position.
Thoroughly inspect ECM connector J1/P1 and permanent timing calibration sensor connector J78/P78. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Check the harness and wiring for abrasion and for pinch points from the timing calibration sensor to the ECM.Expected Result:All connectors, pins, and sockets should be completely inserted and coupled. The harness and wiring should be free of corrosion, abrasion, and pinch points.Results:
OK - Proceed to Test Step 2.
Not OK - Repair: Repair the circuit.Verify that the repair eliminates the problem.STOPTest Step 2. Check the Sensor
Disconnect the permanent timing calibration sensor from connector J78/P78.
Measure the resistance between J78:1 (Signal −) and J78:2 (Signal +).Expected Result:Resistance should be 110 to 220 Ohms.Results:
OK - Proceed to Test Step 3.
Not OK - The sensor is bad.Repair: Replace the sensor.Verify that the repair eliminates the problem.STOPTest Step 3. Check the Harness for Shorts
Disconnect ECM connector J1/P1 and disconnect the permanent timing calibration sensor from connector J78/P78.
Measure the resistance between the following terminals:
P78:1 (Signal −) and P78:2 (Signal +)
P78:1 (Signal −) and engine ground
P78:2 (Signal +) and engine groundExpected Result:The resistance should be greater than 20,000 Ohms.Results:
OK - Proceed to Test Step 4.
Not OK - There is a short circuit in the harness.Repair: Repair the circuit.Verify that the repair eliminates the problem.STOPTest Step 4. Check the Resistance through the Harness
Illustration 2 g00714139
ECM connector P1
Disconnect ECM connector J1/P1 and disconnect the permanent timing calibration sensor from connector J78/P78.
Use a suitable piece of wire to short P78:1 (Signal -) and P78:2 (Signal +).
Measure the resistance between P1:12 (Timing Cal −) and P1:18 (Timing Cal +).
Remove the wire short.Expected Result:Resistance should be less than 10 Ohms.Results:
OK - The ECM is not reading the sensor correctly. Proceed to Test Step 5.
Not OK - There is an open circuit or excessive resistance in the harness.Repair: Repair the circuit.Verify that the repair eliminates the problem.STOPTest Step 5. Check the Signal Voltage at the ECM
Illustration 3 g00714139
J1/P1 breakout
Install a 7X-1715 Adapter Cable (40 Pin Breakout) at ECM connector J1/P1. Reconnect all of the connectors.
Start the engine.
Measure the AC voltage between P1:12 (Timing Cal −) and P1:18 (Timing Cal +).
Turn the keyswitch to the OFF position.Expected Result:The signal voltage should be greater than 6.0 VAC.Results:
OK - A valid signal voltage appears at the ECM. Proceed to Test Step 6.
Not OK - A valid signal is not reaching the ECM.Repair: Perform the following procedure in order to isolate the problem:
Recheck the harness and the connectors for shorts, opens, and excessive resistance.
Ensure that the sensor is not positioned over the timing pin hole in the flywheel when the air gap is adjusted, or damage will result.
If the problem is not resolved, adjust the sensor so that the air gap is approximately 1.0 mm (0.04 inch).
Recheck the signal voltage at the ECM.Verify that the repair eliminates the problem.STOPTest Step 6. Check for Diagnostic Codes
Turn the keyswitch to the OFF/RESET position.
Connect ET to the service tool connector.
Start the engine.
Check for active diagnostic codes on ET.Expected Result:277-08 "Timing Calibration signal abnormal" should no longer be active.Results:
OK - The sensor is working properly.Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.STOP
Not OK - A valid signal appears at ECM connector P1, but the ECM is not reading the signal properly.Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM" before replacing the ECM.STOP