SHIM 5L3558 - Caterpillar

The fan speed sensor is a digital sensor that provides a speed signal from the engine cooling fan to the Electronic Control Module (ECM). The ECM controls the speed of the fan by varying the current to the fan speed solenoid. The ECM attempts to keep the fan within 50 rpm of the desired fan speed.The fan speed sensor receives a regulated 8.0 0.5 VDC supply voltage from the ECM. The fan speed sensor provides a pulse width modulated signal to the ECM that represents the speed of the fan. The frequency of the output is between 0.83 Hz and 30 Hz. The frequencies represent fan speeds from 50 rpm to 1500 rpm.Note: Refer to Troubleshooting, "Digital Sensor Supply Circuit - Test" if the ECM has detected a problem with the digital sensor supply voltage.
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