Use this procedure to troubleshoot the electrical system if a problem is suspected with the cooling fan speed sensor or if the diagnostic code in Table 1 is active or easily repeated.
| Diagnostic Codes Table | ||
|---|---|---|
| Description | Conditions which Generate this Code | System Response |
| 544-2 Engine Cooling Fan Speed Sensor : Erratic, Intermittent, or Incorrect | The signal from the fan speed sensor is intermittent or the signal has been lost. | The code is logged. |
| 544-8 Engine Cooling Fan Speed Sensor : Abnormal Frequency, Pulse Width, or Period | The signal from the fan speed sensor is intermittent or the signal has been lost. | The code is logged. |
The engine cooling fan speed sensor provides a signal to the Electronic Control Module (ECM). The ECM controls fan speed by varying the current to the fan control solenoid.
Note: The variable fan speed control uses the air temperature sensor for the inlet manifold to control the engine cooling fan speed. To prevent the engine cooling fan speed from unnecessarily increasing, the air temperature sensor for the intake manifold is ignored for a period of 90 seconds after the engine start-up.
The sensor outputs a frequency that is directly proportional to fan speed. The sensor generates a signal pulse for each revolution of the fan. The output frequency varies between 466 Hz to 1073 Hz over the speed range between 200 rpm and 1150 rpm.
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| Illustration 1 | g01704454 |
Schematic for the fan speed sensor | |
Test Step 1. Inspect Electrical Connectors and Wiring
- Turn the keyswitch to the OFF position.
- Thoroughly inspect ECM connector J1/P1, ECM connector J2/P2, and all other connectors in the wiring harness. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
- Perform a 45 N (10 lb) pull test on each of the wires that are associated with the fan speed sensor.
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| Illustration 2 | g01713294 |
P1 terminals that are associated with the cooling fan speed (P1-32) Fan speed sensor + (P1-33) Fan speed sensor - | |
- Check the allen head screw on each ECM connector for the proper torque. Also, check the allen head screw on the customer connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
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.
Results:
- OK - The harness and connectors appear to be OK. Proceed to Test Step 2.
- Not OK - There is a problem with 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.
STOP
Test Step 2. Check the Status of the Engine Fan Speed with Caterpillar Electronic Technician (ET)
- Turn the keyswitch to the OFF position.
- Connect Cat ET to the service tool connector.
- Turn the keyswitch to the ON position.
- Access the "Fan Override Test" under the "Diagnostics" menu.
- Start the "Fan Override Test" on Cat ET. Set the fan speed to 500 rpm.
- Use a 1U-6602 Photo-Tachometer to determine the actual speed of the fan.
- Compare the engine fan speed that is reported by Cat ET to the actual engine fan speed that is reported by the photo-tachometer.
- Deactivate the "Fan Override Test".
- Turn the keyswitch to the OFF position.
Expected Result:
The actual fan speed is within ± 50 rpm of the engine fan speed that is reported by Cat ET.
Results:
- OK - The engine fan speed is within the desired rpm range.
Repair: The sensor is operating correctly. There may be an intermittent electrical problem in a connector or in the harness. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect".
STOP
- Not OK - The engine fan speed is not within the desired rpm range. Proceed to Test Step 3.
Test Step 3. Measure the Resistance for the Fan Speed Sensor at the Sensor Connector
- Turn the keyswitch to the OFF position.
- Disconnect the sensor connector from the wiring harness.
- Measure the resistance between terminal 1 and terminal 2 at the sensor connector.
- Restore all connectors and wiring to the original configuration.
Expected Result:
The resistance measures approximately 1050 ± 100 Ohms.
Results:
- OK - The resistance measures approximately 1050 ± 100 Ohms. Proceed to Test Step 4.
- Not OK - The resistance did not measure approximately 1050 ± 100 Ohms.
Repair: Replace the fan speed sensor. Verify that the replacement corrects the original problem.
STOP
Test Step 4. Measure the Resistance for the Fan Speed Sensor at the ECM Connector
- Disconnect the P1/J1 ECM connector.
- Measure the resistance between P1/33 and P1/32.
- Restore all connectors and wiring to the original configuration.
Results:
- OK - The resistance measures 1050 ± 100 Ohms.
Repair: Replace the ECM. Refer to Troubleshooting, "ECM - Replace". Verify that the problem is resolved.
STOP
- Not OK - The resistance does not measure 1050 ± 100 Ohms.
Repair: Repair the wiring between the ECM and the sensor.
STOP