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The 2000–2002 Pontiac Sunfire is a sedan model.

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Check engine light on due to fan system not working

The radiator cooling fan is not working properly. I have bypassed its own system installed a aftermarket relay to have the fan working at all times. But now the check engine light is on with a code that translates to cooling fans system not working properly. Where can I find an accurate schematic or plan of diagnosis to have this fixed the right way?

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You probably have a faulty engine coolant temperature sensor or if the sensor tests OK, a wiring problem between the sensor and the ECM. Hopefully the problem is not in the ECM.

If the sensor is faulty, replace it and restore the fan wiring to the way it was and see how it goes

This sensor is connected to the ECM, which controls the radiator fans.

Here is a link that may be of some help.

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That was the first thing that I had thought of as well. I changed the sensor and also the harness it comes with and did not help at all. Nearest I understand it's something to do with the fan control circuit. But I can't find any information on that circuit


Hi @rdavis1976 ,

Found this info which I hope may help. It says that there are 2 temp sensors (in the '97 model anyway so hopefully not different for yours .

On a 97 Sunfire 2.2, you have two sensors,

one is a coolant temp sensor , that the signal is sent to the temp gauge, in the instrument panel.

And one that is called engine temp sensor, and this one sends it signal to the PCM were it is sent to ground and completes the circuit to the coolant fan relay.

coolant temp sensor

Part: ECH TS4052

Product Line: Echlin Ignition

List Price 30.51

engine temp sensor

Part: ECH TS4015

Product Line: Echlin Ignition

List Price 36.90

Also these 2 links have wiring diagram. Again hopefully suitable to your model.

here is the link it all came from


That is by far the most information that I've came across. I really does hope this helps. I won't have a chance to check into it for a couple of days. But I will definitely update you when I find something. Thank you so much for your help and information


If you unhook the cooling fans and put a toggle in will it set a code??


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I have a 2010 m2 that someone before me added a fan switch to and it sometimes will cause the check engine light to come on. Sometimes it goes off with the switch and other times it takes the ecm kicking on the fan to make it go off. Turning the switch on doesn’t always cause the light to come on immediately so it is kind of hit and miss. The only thing I can think of that may cause my problem is the ecm may be monitoring something like temp, fan state on/off or something similar at various times and registers a reading that it f finds out of tolerance based off of it’s own output commands and throws the light on until it thinks it has been corrected.

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Randall Davis sarà eternamente grato.
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