879288038 Mercruiser NUT

Illustration 1 g01013813
Schematic
Illustration 2 g01013815
P1 ECM connector
Test Step 1. Inspect Electrical Connectors and Wiring
Turn the keyswitch to the OFF/RESET position.
Thoroughly inspect the J1/P1 ECM connector, the J3/P3 machine connector, and all other connectors in the wiring harness. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details. Expected Result:All connectors, pins, and sockets are completely inserted and coupled. The harness and wiring are free of corrosion, of abrasion, and of pinch points. All connections and grounds are tight and free of corrosion.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 Status of the Engine Fan Speed
Connect the Caterpillar Electronic Technician (Cat ET) to the service tool connector.
Start the engine. Ensure that the keyswitch is in the ON position.
Compare the status for "Engine Fan Speed" to the status for "Desired Engine Fan Speed" on Cat ET.
Turn the keyswitch to the OFF/RESET position. Expected Result:"Engine Fan Speed" is within 50 rpm of "Desired Engine Fan Speed".Results:
OK - The sensor is operating correctly.Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.STOP
Not OK - Proceed to Test Step 3.Test Step 3. Check the Digital Sensor Supply Voltage at the Sensor Connector
Disconnect the J508/P508 harness connector for the fan speed sensor.
Turn the keyswitch to the ON position.
Measure the voltage across P508:5 (+8 VDC) and P508:2 (Return).
Turn the keyswitch to the OFF/RESET position. Expected Result:The digital sensor supply voltage is 8.0 0.5 VDC.Results:
OK - The supply voltage is reaching the sensor. Proceed to Test Step 8.
Not OK - The supply voltage is not reaching the sensor. Proceed to Test Step 4.Test Step 4. Check for Shorts in the Harness Between the Fan Speed Sensor and the ECM
Disconnect the J1/P1 ECM connector.
Ensure that the J508/P508 connector is disconnected.
Measure the resistance between P1:4 (Digital Sensor +8 VDC) and chassis ground.
Measure the resistance between P1:4 (Digital Sensor +8 VDC) and P1:5 (Digital Sensor Return).
Measure the resistance between P1:32 (Fan Speed Signal) and chassis ground.
Measure the resistance between P1:32 (Fan Speed Signal) and P1:5 (Digital Sensor Return).
Measure the resistance between P1:4 (Digital Sensor +8 VDC) and P1:32 (Fan Speed Signal). Expected Result:The resistance for each measurement is greater than 20,000 Ohms.Results:
OK - Proceed to Test Step 5.
Not OK - There is a short between the ECM and the fan speed sensor.Repair: Repair the circuit.STOPTest Step 5. Check for Open Circuits in the Harness between the Fan Speed Sensor and the ECM
Turn the keyswitch to the OFF/RESET position.
Ensure that the J1/P1 ECM connector is disconnected.
Use a suitable piece of wire to short P1:4 (Digital Sensor +8 VDC) and P1:5 (Digital Return).
Ensure that the J508/P508 connector is disconnected.
Measure the resistance between P508:5 (+8 VDC) and P508:2 (Return).
Measure the resistance between P508:1 (Signal) and P1:32 (Fan Speed Signal). Expected Result:The resistance is less than 10 Ohms.Results:
OK - Proceed to Test Step 6.
Not OK - There is an open circuit in the wiring harness between the fan speed sensor and the ECM.Repair: Repair the circuit.Verify that the repair eliminates the problem.STOPTest Step 6. Check the Digital Sensor Supply Voltage at the ECM
Turn the keyswitch to the ON position.
Measure the voltage across J1:4 (Digital Sensor +8 VDC) and J1:5 (Digital Return). Expected Result:The digital sensor supply voltage is 8.0 0.5 VDC.Results:
OK - The ECM is producing a valid supply voltage. Proceed to Test Step 7.
Not OK - The ECM is not producing a valid supply voltage.Repair: You may need to replace the ECM. Refer to Troubleshooting, "Replacing the ECM" before replacing the ECM.Verify that the repair eliminates the problem.STOPTest Step 7. Check the Signal Frequency at the ECM
Reconnect the J508/P508 harness connector.
Install a 7X-6370 Adapter Cable As (3 Pin DT Breakout) at the J1/P1 ECM connector.
Start the engine. Ensure that the keyswitch is in the ON position.
Accelerate the engine to high idle.
Use Cat ET to set the desired fan speed to 800 rpm.
Measure the frequency of the signal between P1:32 (Fan Speed Signal) and P1:5 (Digital Return) at the breakouts. Expected Result:The frequency is between 0.83 Hz and 30 Hz.Results:
OK - Proceed to Test Step 8.
Not OK - The fan speed sensor is faulty.Repair: Replace the fan speed sensor.Verify that the repair eliminates the problem.STOPTest Step 8. Check the Status of the Engine Fan Speed
Remove the breakout and reconnect the J1/P1 connector.
Start the engine. Ensure that the keyswitch is in the ON position.
Accelerate the engine to high idle.
Compare the status for "Engine Fan Speed" to the status for "Desired Engine Fan Speed" on Cat ET. Expected Result:"Engine Fan Speed" is between 50 rpm and 1500 rpm and "Engine Fan Speed" is within 50 rpm of "Desired Engine Fan Speed".Results:
OK - The sensor is operating correctly.Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.STOP
Not OK - There may be a problem with the fan speed solenoid, or there may be a problem with the motor for the fan.Repair: Refer to Troubleshooting, "Engine Fan Control Solenoid Circuit - Test".STOP