well my CEL came on again today while driving home... so i got on the computer to refresh my memory on the key trick. did it and got 2 seperate codes. 12 and 37.... i believe.... i had a hard time keeping up with the flashes and pauses so i wanted a second opinion. i drove to advanced auto and had them scan it for me. the scan reads as follows.

ENG: 72/P0420
Catalyst 1/1
Efficiency

So now i am confused.... does anyone have any experience with this? the jeep doesn't run to bad. it has somewhat of a rough idle but doesn't stall or wanna stall. I just replaced my computer, ignition coil, and my upstream o2 sensor. please help.... 96 se 4.0l auto

 

420 is pretty straight forward, it means the cat is bad. but, jeeps are not very tight on monitoring that back then. if you clear it, it should stay off for a while. but eventually you will need a new catalytic converter.

 

sorry bout the confusion... i was unclear on how to read the code that was given by advanced auto. That's weird because the po said the exhaust was replaced once b4. maybe he just meant from the cat back was replaced. it wouldn't be the downstream o2 sensor would it?

 

nope on the 02. the computer uses both oxygen sensors to monitor the cat. the computer knows if the oxygen sensors readings are unreliable, and will give a code for one of them.

 

dang you guys are good!!!

 

is that 2 1/4" pipe... weld on clamp on? thanks

 

You're better off having it welded up properly by a muffler shop. They won't charge a fortune for a small job like that. Shop around if it helps you get a better price. In my opinion, clamps are fine for a CBE but the Cat should be welded.

 

i don't know about that, its bolted on from the factory. makes it easier to change parts down the road. what i do hate is crappy exhuast shops welding in mufflers and parts that aren't direct fit, then its a huge pain later to replace any other part.

either way is fine, welding is less problematic such as coming loose, or clamps rusting off and rattling. but direct fit is easier to work around later.

 

Typically on an XJ, your OEM muffler and tailpipe will rot out long before the Cat. I'm quite sure the PO did just replace the muffler and tailpipe and then added "new exhaust" to his ad. Cats are expensive to replace. I'm sure you would have paid about $200 more for your Jeep if he'd had to replace the cat.

 

i crawled under it today and wow what a mess!! its clamped and tacked on. i assume thats factory. i could see the muffler and tail pipe and that was def replaced and could be replaced again because the bottom of the muffler is rotting out again. I think my best bet would be having my local muffler shop re-do the hole thing. cat, muffler and pipe. i just don't want anything ridiculously loud but i def don't want stock. and CHEAP!!!!

 

12 battery was disconnected
37 Shift indicator light failure, 5-speed
OR park/neutral switch or torque converter unlock circuit open or shorted

 

i'm going to my buddies shop to get it read again.. let you guys no later tonight..

 

read the code again and it says 420 as previously stated and also said something about bank 1 which I imagine is just the o2 sensor that is sensing the problem? cleared the code and drove it for 30 minutes and no CEL yet. i am ordering a new cat for it and a new muffler. weld it up nice and tight!!!

 

I got my converter from Summit Racing for 100 bucks. It's application specific, and was a perfect fit.

Don't be so sure to just change out the O2 just because it says O2. This is a marketing ploy that Advanced and Vato Zone use to sell parts. The common man is ignorant to CEL problems, and the clown behind the scanner shows him/her "see; it says you need an O2"....so you buy an O2 sensor, then the light comes back on. Now you're pissed and you take it to a shop. The mechanic finds out that the heater element inside the O2 has lost a ground, due to a bad connection where it plugs into the computer harness.

Do more research is what I'm trying to say. Don't just go out and do parts swapping. Find some troubleshooting trees using Alldata, or Mitchell On-Demand. Pay for it if you have to. The troublehsooting trees are what the shops use. Be patient.

 

He's correct; P0420 is "Catalyst efficiency below threshold". This is a OBDII generic code- meaning that the rear O2 isn't seeing a change from what the front is reading. The rear sensor should switch from rich to lean at a slower rate than the one in front of the converter. Both of the sensors are working, otherwise you wouldn't have that code.