I just installed a new muffler on my 94 Cherokee and when it gets up to running temp the check engine light comes on. Has anyone else had this problem or know why it is happening?

 

Possibly an O2 sensor. That would be my guess.

 

pull the code then post it then we can help you

 

What code?

 

Go to Advance Auto Parts and have them hook up their programmer to tell you why your check engine light is on in the first place. They will do it for free and can either tell you whats wrong or will give you what code it is.

 

Here's how to check your own.-> Computer codes

 

according to this its my cooling fan relay. whats next?

 

My light is alwayts on, I'm just used to it now... they tell me the front O2 sensor is getting too many amps? I donno, I drive it... it goes. haha

 

i would try and replace the coling fan relay its under the hood in the fuse block they are cheep after you change it reset your computer to make sure an dclear the code

 

whats the easiest way to reset your computer

 

Remove both bat cables and hold them together for 10 seconds. That erases everything. After reconnecting cables take it for a good drive, at least 20 miles, so that it can relearn the parameters.

 

lol, what does holding the cables together do?

 

It drains any residual power in the computer so that the codes will be erased.
That way you don't have to wait for the 50 key-starts (with no recurrence) for the codes to erase.