C7.1 Engines and Generator Sets Caterpillar

Cooling Fan Speed - Test

Usage:

C7.1 770

Use this procedure to troubleshoot the electrical system if a problem is suspected with the cooling fan speed sensor.

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.

The engine cooling fan speed sensor receives a supply voltage from the ECM. 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 5 Hz to 180 Hz over the speed range between 50 rpm and 1800 rpm.

During the following procedure, refer to the electrical schematic for the application.

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Table 1
Required Tools
Tool	Part Number	Part Description	Qty
A	351-8635	Tachometer Kit	1

Complete the procedure in the order in which the steps are listed.

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Table 2
Troubleshooting Test Steps	Values	Results
1. Check the Status of the Engine Fan Speed A. Turn the keyswitch to the OFF position. B. Connect the electronic service tool to the diagnostic connector. C. Turn the keyswitch to the ON position. D. Access the "Fan Override Test" under the "Diagnostics" menu. E. Start the "Fan Override Test" on Cat ET. Set the fan speed to 500 rpm. F. Use Tooling (A) to determine the actual speed of the fan. G. Compare the engine fan speed that is reported by the electronic service tool to the actual engine fan speed that is reported by Tooling (A). H. Deactivate the "Fan Override Test". I. Turn the keyswitch to the OFF position.	Fan Speed	Result: The engine fan speed is within ± 50 rpm. 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". Result: The engine fan speed is not within ± 50 rpm. Proceed to Test Step 2.
2. Check the Sensor Supply Voltage at the Sensor Connector A. Turn the keyswitch to the OFF position. B. Disconnect the sensor connector from the wiring harness. C. Turn the keyswitch to the ON position. D. Measure the sensor supply voltage between terminal 2 and terminal 3.	Supply Voltage	Result: The supply voltage is not reaching the sensor. Repair: Refer to Troubleshooting, "Sensor Supply - Test". Result: The supply voltage is reaching the sensor. Proceed to Test Step 3.
3. Check the Signal Frequency at the Sensor Connector A. Turn the keyswitch to the OFF position. B. Remove the wire from terminal 1 on the sensor side of the connector. Connect the sensor connector. C. Turn the keyswitch to the ON position. D. Access the "Fan Override Test" under the "Diagnostics" menu on the electronic service tool. E. Start the "Fan Override Test" on the electronic service tool. Set the fan speed to 800 rpm. F. Use a multimeter to measure the frequency between the signal wire from the sensor and engine ground. G. Deactivate the "Fan Override Test". H. Turn the keyswitch to the OFF position. I. Restore all connectors and wiring to the original configuration.	Sensor Frequency	Result: The frequency is approximately 80 Hz. The engine cooling fan speed sensor is generating the correct signal. Repair: Repair the harness or replace the harness. Verify that the fault is resolved. Result: The frequency is not approximately 80 Hz. Repair: Replace the fan drive assembly. Verify that the fault is resolved. If the fault is still present, contact the Dealer Solutions Network (DSN).