Radiator fan only works when temperature sensor unplugged

Fan will default to on with no signal from the sensor, the only other item would be the fan control module. I only have a location as being at the left front of engine compartment. The PCM is also involved in this circuit, but I would suspect the control module, a dealer scan will show if this module is faulty.

Please post back what they find, as it can help others here.

OK, I thought that may be the case, often the case is they make these units integral and you have to replace more than is required to fix the car.

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In his case the control module was a part of the fan itself so to replace it requires replacing the entire module as one piece. Happens a lot where a control unit is either molded into or is actually inside the part it controls.

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Well no control signal from the PCM would definitely cause that. However I'm not sure it's the PCM that is the problem, That is because the fan still turns on when you disconnect the ECT plug, and works with the A/C. Both of those use the same circuitry inside the PCM to turn on the fan. I suppose it could be something on the board between the ECT input and the fan output that is causing that problem.
I would do some testing though just to be sure. It is a simple system as cooling fans go. The ECT sensor tell the PCM the temperature, at 209 degrees the PCM sends a pulsed power signal to the fan control module. That signal keeps getting faster as the temperature rises. The control module gets that signal and uses larger power transistors to pass the pulsed signal to the fan.
I would verify both of the Black ground wires are good.
As the fan does work when the A/C is on the power feed should be OK That leaves just the ECT and the PCM signal.
I would check the wiring to the temperature sensor very close for any issues. It operates using a thermistor which converts a temperature into a resistance. Any added resistance from corrosion or a loose pin can cause a problem.
You say you changed the sensor, how about an odd test. Unplug the sensor wiring and plug in the old sensor. Now just turn on the key and use a small torch or even a candle to heat the old sensor on the area that was inside the engine. What does the fan do?

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