Maybe whilst putzing around with the thermostat, the adjacent wire to his temperature sensor (not temp. gauge sending unit) got jostled enough to give back a good connection that he didn't know he didn't have. That temp. sensor plays a part with with telling the computer what to do when with other sensors, etc. His situation sounds like a coinkidinky to me too.

 

There is no coincidence involved here. I have had this EXACT same issue with 3 GM vehicles: an 98 Olds LSS 3.8l, a 2001 Camaro 3.8l, and an Olds Silhouette 3.4l.

Thermostat stuck open. Engine doesn't heat up properly and after a few running cycles, it will throw the code for coolant temp below operating parameters, shut off the temp gauge, and turn the fans on permanently. This is controlled by the PCM. Again, identical issue with all three cars. Replace the thermostat (a real pain on the 3.4l minivan btw) and issue is solved. It is a common and well known issue on the minivan; not so much on the 3.8l vehicles.

 

same symptoms in my 02 firebird 3.8 , took out the thermostat and it was stuck in the open position ..

the plunger was stuck on 2 little prongs in the body of the thermostat ..

installed a new thermostat and the gauge and fans have been working fine for 2 days.. ..

 

Anyone have the fan schematic section they couls post? I am having issues with my fans while running the AC only running slow. Most cars when you turn the AC on teh fan go full of. Anyone have any feedback on this?

 

http://shbox.com/1/fan_schematic_1995.jpg

There's the electrical schematic. As for your question about fans, here's my understanding of how they *should* work...

Fan is OFF when A/C is off (unless engine temp is high). Fan is on LOW when A/C is on and pressure is below a certain point (I forget what the switch-point is). Fan comes on HIGH when the pressure is higher than that level.

If A/C is off, the fans should come on LOW at a certain temp and then HIGH at a higher temp.

 

I had same exact problem. I changed my cts, swapped out fan relays, cleaned connectors, and checked over wires..no change. took it to the shop and they changed thermostat. works like new again.

 

the gauge does not have its own sensor on the 2002 3.8 it gets the signal from the coolant temp sensor. and when it goes out the fans will kick on full an your gauge will stay below 100.
I have/had the same issue over the years with multiple Camaro's and Fire chickens. yes some earlier yrs had 2 sensors on for the gauge and on for the ECM. but when OBDII came out there was no need for it.