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1998 jaguar xk8 31,000 miles . upon cold start both fans do not run . sitting idling after sometime both fans come on together and run smoothly. after more running time fans run in high speed mode and continue to do so. after shutting down engine , fans come back on in highspeed mode for a few minutes then shut off. car does not appear to run hot ever. (based on dashboard gauge)ACTUAL QUESTION IS FANS RUN IN HIGH SPEED MODE CONTINUOUSLY AFTER WARM UP, NEVER HAPPENED BEFORE.
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Is your check engine light on? If the coolant temperature sensor is missing or is shorted high or low then it can run the fans full speed to protect the engine since it doesn't know actual temperature.
Since the fans run on their own after shutting the car off I'm assuming you don't' have a coolant sensor related issue. Most likely the problem is with the fan control module or possibly it's wiring.
The module is basically a solid state relay that controls fan speed variably based on a signal from the ECM. When the module fails internally it will usually cause the fans to run on high all the time, sometimes to the point of running the battery down. Odds are your module is bad.
It's also possible that the problem could be with the ECM or the control wire between it on the fan module. If the circuit shorts to ground it will cause the fans to run full speed. This is a possibility but not as common as the module itself failing.
makes , i agree with your determination, please be specific in helping me locate the fan control module. and no my check engine light is not on.
thanks for the quick responce and detailed information !!!