i just check the codes on my xj and i got 3 of them
#13(MAP sensor)
#35(cooling fan)
#41(alternator)

im not worried about the 35 cuz its prbly being thrown with the switch i wired to it, but the 35 and 41 got me worried. i looked and i have seen different answers on what each are exactly. if anyone has any info on these that could help that would be great

 

does any one know?

 

Check alternator voltage at the battery (clean the posts too) The battery should be close to 13V with engine off, and around 14 with engine running.
For the MAP sensor, i'd check the vacuum at the MAP end of the hose and make sure it's not cracked or loose. The sensor itself can be tested, but I don't know the 'how to' on it.

 

http://www.jedi.com/obiwan/jeep/dtc.html

so if a buddy by you has a spare map sensor then swap it out and check your codes again...

i wouldn't worry about the cooling fan code... if you have a switch wired into your electric fan then thats why its showing up.

As far as your alt, look for some frayed wires or anything that looks outta place.

 

now i found a map sensor on my parts xj that worked and i cleaned my terminals that werent that bad to begin with, and then i reset the codes. i have not started it yet, but i checked the codes first and now its only flashing a code 12 at me. im sure i will get more once i start it, but what would cause a code 12? and also with the alternator one, it squeals pretty bad on start up and also when you got just the headlights, heater and radio going all at the same time.would upgrading to a zj 136 alt. fix that or would i be wasting my time

 

I think code 12 means 'battery was disconnected' (it was thanking you for cleaning the terminals) Then you should see code 55 for 'end of codes'