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.