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zhero21 02-26-2012 10:27 AM

Which cat converter is my problem?
I have a 01 TJ. Engine code told me something like "cat converter is bad".
I have 2 off my headers and 1 main. What is the easiest way to diagnose which one I need to fix. Im in college so the easier, the better. Also, if it is the front 2, will aftermarket headers replace the need to fix them?
Ill try to respond to any questions as quick as possible. thanks for help

zhero21 02-26-2012 10:27 AM

4.0L manual

zhero21 02-28-2012 01:27 PM


Dextreme 02-28-2012 01:58 PM

I would let the engine come up to running temp then zap each with a infrared thermometer.

"A good converter will usually run 100 degrees F hotter at its outlet than its inlet. Little or no temperature change would indicate low efficiency, or a problem with the converter's air supply. "

Good tool to have: Non-Contact Infrared Laser Thermometer

C.L. 02-28-2012 02:16 PM

Begin with your engine and ignition off. Without starting the engine, cycle the ignition: On Off On Off On, taking about 1 second per cycle. After a couple seconds at the last "On", your odometer will flash some codes at you. Write them down and post them up. If one of the cats is bad, it is probably tripping an O2 sensor. The computer can narrow it down to which bank of sensors is seeing the problem.

zhero21 02-28-2012 02:27 PM

P0420 and P0455. Im gunna do my own research while I wait to hear back from you. Thanks!

CoyoteOn2 02-28-2012 02:36 PM

P0455 (M)
Evap Leak Monitor Large Leak Detected
A large leak has been detected in the evaporative system.

P0420 (M)
1/1 Catalytic Converter Efficiency
Catalyst 1/1 efficiency below required level.

C.L. 02-28-2012 02:58 PM

The 0455 is often just a loose/broken gas cap. Make sure yours is tight, and if it's the ratcheting type give it a few clicks. If that doesn't clear it after a few days crawl under there and look for a couple metal lines coming off the top of the gas tank and running forward along the body/frame. If one of them is rusted through or crimped, it could be causing the same code. You can also check the lines going into your evap canister (black box under the hood; drivers side, against the fender) to see if the rubber is rotting.

0420 indicates bank 1, which i believe is the forward mini-cat. The error is SUPPOSED to indicate that the cat isn't removing NO/NO2 or somesuch at the required efficiency, but it is also possible that the sensors are just on the edge of failing. O2 sensors are something like $30 each and screw in, whereas a cat is a few hundred and involves cutting/welding... I would replace the bank 1 upstream and downstream O2 sensors before messing with the cat.

zhero21 02-28-2012 03:02 PM

I just crawled under and took a look at it. It looks like there are o2 sensors pre and post BOTH minicats. Am I looking at the right thing? If this is the case, does this still mean I should try to replace all 4 up front?

zhero21 02-28-2012 03:28 PM

Also looking around, I found this hanging down there, but I dont see anything to connect to it. Anyone have any idea. It is paired with some wires that has a connector that goes to a 02 sensor I believe

C.L. 02-28-2012 06:59 PM


Originally Posted by zhero21 (Post 2084285)
I just crawled under and took a look at it. It looks like there are o2 sensors pre and post BOTH minicats. Am I looking at the right thing? If this is the case, does this still mean I should try to replace all 4 up front?

The mini-cat closest to the front of the Jeep is considered bank 1, the mini-cat closest to the back of the Jeep is considered bank 2. There are different error codes for bank 1 vs bank 2, yours threw the bank 1 code. I would start by replacing the 2 O2 sensors in bank 1. Or at least make sure that plug hanging down isn't supposed to be attached to one of your sensors.

apexkw 02-29-2012 08:03 AM

Just throwing this out there but this place had some of the cheapest oem style replacements cats I found. Welcome - Eastern Manufacturing | World-class quality and innovation have made Eastern Catalytic a market leader in catalytic converters. my 03 i-6 is throwing the same 0420 code and after doing to o2 sensor swap i'll be swapping the cats out soon.

MabCab 03-03-2012 08:27 PM


So i tried checking the prices for the cats on Eastern and could not get a price. Do you have to be a dealer or something? What price did you come up with, I am looking at part # 20367.

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