I installed a new t stat a little while ago, maybe 6 months ago. I left the engine running a while and the fan did not turn on. It used to work before this new t stat. The fan is OEM as well. Any ideas?
The reason for the lapse in time asking about the fan not running is that I have not driven this Jeep in a while, regularly. I mostly use it to pull my trailer in and out of the backyard, plus there's a large crack across the windshield that I have not replaced due to no comprehensive coverage. It's $275 to replace.

 

What temps did you get up to?
I assume you're talking about the aux fan which I believe doesn't turn on until 226F or the ac/defrost is on.

 

Pull the temp sensor connector, it will cause the PCM to activate the electric fan.

 

That works for 97+
Under 96 too?

 

I have a dummy gauge so no accurate numbers.

I pulled the temp sensor connector and it did not kick on.

But it does kick on when the a/c is on.

 

Do you have AC?

 

Read post 2. Turn on the ac and see what happens

 

Yes

 

Nvm, I just missed post #5 there

Ok so the fan works- the pcm "just doesn't turn it on". This has nothing to do with your thermostat, except:
It'll only come on when you run hot (see my post in other recent thread). It won't come on if you're not running hot , nor have no AC selected.
So, if we piece all things together: your new thermostat is working, you're not running hot, the pcm doesn't have to turn the aux fan on the fan works correctly when you select AC.

 

Which temp sensor connector did you pull...the one in the thermostat or the one near back of block

 

I think it's 218*F.

 

The one at the front.

 

So the other issue I have is that when I crank it over the check engine light comes on, that's new and the selector for vents won't turn off. I can't check to see if the aux fan kicks on when the a/c is on because I am not sure if it's the air just being on or the a/c. Also, I noticed that when the selector is in the heat mode that it really doesn't heat up even after keeping it on for several minutes.

 

if you disconnected the connector on the thermostat, and the fan did not turn on...you have issues with your fan/wiring/fan relay or pcm

 

Have it checked for codes- its trying to tell you something