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Update

This question seems to be attracting a lot of views, so I guess a lot of people are having the same problem.

Just to be clear, the problem with MY fans specifically seemed to be caused by my new temp sensor being faulty. This isn't likely to be your problem, but don't rule it out. There are some other great diagnostics suggested below for other possible reasons the fans aren't running.

There was a bigger problem with overheating with this car, even after the fans were running correctly. The stock engine comes with a plastic intake manifold gasket, which is prone to failure. It leaks coolant into the cylinders and causes inefficiency in the cooling system, leading to low coolant and overheating. You can replace this gasket with a metal one, the repair is a little involved but I managed with a Haynes manual. Good luck!

Original Question

My 2000 Pontiac Grand Am GT (6 cy/3.4L) has been having cooling issues. I started by replacing the thermostat and performing a flush & fill on the radiator. This didn't seem to resolve the issue -- the engine still overheats when at a stop.

This lead me to suspect the fans, so I tested the fans themselves (independent dual electric cooling fans). They do not start when the engine is warm... this is the problem.

I wired each fan directly to the battery, both function correctly. Next, I checked the relays, both tested operational. If I disconnect the temperature sensor, both fans come on immediately. So, I replaced the temperature sensor.

The problem persists; the engine will reach 200, the thermostat opens (determined by watching the temp. gauge), but the fans do not start. If I disconnect the (new!) temperature sensor, both fans start. I have read that turning the air conditioning on should also cause the fans to turn on, this does not happen (with the temp. sensor plugged in), not when then engine is cool or hot.

I am at my wits end as to what to check next. I am prepared instead to hardwire the fans to the ignition switch. Can anyone give me any ideas of any further diagnostic steps before I give up and take the "duct tape solution"? This is my wife's daily driver, so the pressure is on! Thanks in advance.

Chris
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5 Answers5

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Don't be discouraged by a new part not working. My family runs a shop, and we get defective parts all the time.

There is a table located here that shows diagnostic steps you can take. It's for a 1999 model, but 1999-2001 are virtually the same (I own a 2001 G/T model).

Sly
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Hook your temp sender up to a meter and drop it in some boiling water. This should tell you if it's working or not. Personally, I'd just disconnect it until you get the issue figured out -- running the fans continuously isn't going to hurt anything, it'll just be loud.

TMN
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The problem might be with the body control module (BCM). The PCM sends the signal to the BCM, which turns the fans on. Or you can buy a separate temperature fan relay system with a temp probe and bypass the system. It will work as normal cooling when needed only.

Pᴀᴜʟsᴛᴇʀ2
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dumbguy
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Its the connecter that you unplug from the temp sensor. That connection is usually bad and can be fixed by directly putting the wires together or cleaning each connector. Had the same problem on 1998 grand prix gt 3800 series 2

user7626
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your issue is with the temp switch not the temp sensor. the sensor will only operate the fans when it fails to avoid a possible overheating issue ,where as the switch is the fans main controller via ecm. the switch should be on the radiator itself or near the water pump.

brian reed
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