fault code
Postmaster
Joined: Oct 2003
Posts: 4,516
Likes: 1
From: SoCal
Sounds like the convertor is shot. Theres an 80K miles federal emissions warranty on the convertor. If you are under 80K, take it to the dealer. If over 80K, take it to a good independant shop.
Last edited by 87 XLT; Oct 8, 2004 at 09:35 AM.
Posting Guru
Joined: Aug 2000
Posts: 1,984
Likes: 2
Welcome to FTE, Jeff. 
That code can mean the catalytic converter is starting to wear out, BUT don't replace it yet. There are other reasons for this code. First check the wiring going to the rearward O2 sensor (the one behind the cat). This wiring harness has a long run that's not secured, and it tends to sag on the top of the cat and get burned. If a wire is burned open or grounded, that will also trigger the catalyst code.
That code can mean the catalytic converter is starting to wear out, BUT don't replace it yet. There are other reasons for this code. First check the wiring going to the rearward O2 sensor (the one behind the cat). This wiring harness has a long run that's not secured, and it tends to sag on the top of the cat and get burned. If a wire is burned open or grounded, that will also trigger the catalyst code.
Postmaster
Joined: Oct 2003
Posts: 4,516
Likes: 1
From: SoCal
Good point, but if the O-2 circuit was open it "should" be throwing a P-O136 "downstream O2 circuit fault." From what i've seen on other posts & read elsewhere, the P-0420 is a pretty good indication that the convertor is shot.
Elder User
Joined: Feb 2004
Posts: 811
Likes: 0
If you get catalyst efficieny code, the sensor works! 99% of the time the cat is the problem. It has lost it's ability to do it's job. Just so you know, I have had trouble with some aftermarket converters. Do a little research and ask and make shure they will stand behind the product if it does't work.
