Just got my first Jeep! 2001 Cherokee Limited 4x4 Automatic. 90,000 miles .Ive had it 2 months and now check engine light codes :
P0303
P0432
P0420
I know the first one is cylinder 3 misfire, but AM I SCREWED!!!
Thanks in advance for ANY help!
The Jeep is in GREAT shape other than these codes!

 

You are correct about the #3 misfire code. The other 2 codes are for the O2 sensors. Since you have the misfire on the cylinder, it's most likely throwing off your O2 readings. You'll need to determine the cause of the #3 cylinder misfire, clear the codes and go from there.

Common problem with XJ's are the #3 cylinder misfire due to heat soak. But could be just a plug or wire just as easily. Check your tune up parts for wear and make sure your injector is firing.

 

Gotta do a tune up. Just go ahead and do wires spark plugs and O2 sensors. I would say cap and rotor...but i believe you have coil packs. Replace those too?

 

The 2000-2001 jeeps with the coil packs really like NGK spark plugs. If you have a different brand I suggest you try the NGK V-Power plugs. @ $2/plug changing plugs won't break the budget and may fix your problem.
No need to replace the coil packs at this time (they are expensive).

If you don't have a OBDII code reader to erase the code you can do a Electronic Control Unit Reset:
http://www.quadratec.com/jeep_knowle...article-89.htm

Even safer to remove both positive and negative and touch them together. If you mistakenly remove the negative cable and touch it to the (still attached) positive there will be big scarey sparks!