Hey yall.

96 cutlass ciera 3.1, when the coolant temp sensor is plugged in the cooling fan will not turn on at all, even at 100 degrees celcius reading from a scan tool, but when its unplugged the fan runs constantly.

Obviously i could just not have a coolant temp sensor but it seems better to have one so if you have any idea on where the problem could be please let me know....

Thanks!

Probably the cooling fan relay ...or then fans themselves?
Got to go ....will let others chime in for help on location..testing etc..

I think most GM'* are programmed to turn on @ 212F low speed and then 226F high speed. At 100*C, you are right close to the low speed turn on point of 212.

If you could find a way to crank the temp up a few more degrees, they may just turn on.
When you disconnect the coolant temp sensor like you did, its normal for the PCM to turn the fans on. Its like a safe mode. This is perfectly normal. My 95 and 97 Bonnevilles did the same thing.

100 celcius might not be hot enough that is only about 215 Farenheit. A lot of vehicles don't turn fans on till about 220 to 230 farenheit. If the fans come on when you unplug the sensor that is normal. So you know the fans do work.

The PCM won't turn the fan on till 220f so at 100c your still a few degrees short of the fan turning on. With the temp sensor unplugged the I believe the PCM sees the open and turns the fan on for engine safety.

Thanks so much guys. Really appreciate it, in fact i haven't seen if they are on at above that temp.
Thanks!

Shouldn't the fans come on low when AC is on or defrost mode is used? Does on the PA.
I should have referenced 100C..to F..just did not have time..work was calling..and had to split.
I've noticed mine come on low in summer around 210F (with AC off) so I think my system is working ok.
Oh and by the way..Welcome to the forum Matt.!

Low or high, depending on system pressures usually.