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Which cat typically causes P0420?

21K views 7 replies 8 participants last post by  csmeance 
#1 ·
When it gets cold, my 2006 with 400 000 km gives a P0420 code every couple of weeks.

This past weekend, I had to drive with the rear hatch open, and definitely rotten egg smell coming from the exhaust.

I called an exhaust place and the guy I spoke to thought it was probably one of the (pre?) cats (that are closer to the exhaust manifold) would likely be the problem. I always figured it would be the other cat under the car.

Any idea which cat would be bad for a P0420 and rotten egg smell?
 
#2 ·
Basically, this means the computer has detected the converter on bank 1 is not storing oxygen as it should. The computer is able to determine this by monitoring the front and rear oxygen sensors and comparing the readings. Basically, if the two oxygen sensor signals are the same, the converter is not working and will flag this P0420 catalyst code.Here are a couple links to consider before you spend money on a new converter.

Now if you want an inexpensive fix you might try this!

 
#3 ·
Holy, jeez, Wilson... What is wrong with you today? Now you're posting links to Scammy Kilmer??

DO NOT FOLLOW THAT CRACKHEADS ADVICE.
 
#4 ·
Is your mdx running rich or burning oil? I guess that could build up in the honeycomb so maybe a cleaning would help but more likely is that the rare earth metal of the honeycomb is just worn out and needs to be replaced. I had to do that an my previous car an Audi a6 and a new cat was 1600 bucks just for the part, might be cheaper these days maybe not... Luckily mdx cats are way cheaper
 
#5 ·
FWIW, when I got the P0420 code, I ended up changing the cat by the firewall. Service manual said low quality gas can cause the code so tried better premium gas first. Some say to try changing the lower O2 sensor before changing the cat.

I ended up getting a Honda cat online. The thing I remember is having to remove the heat shield to take out the cat from passenger side wheel well. You may need PB Blaster or something like it on the bolt threads. I also purchased gaskets for both ends of the cat.

I’m leary of the laquer thinner idea. I suppose it’s diluted and short term but I would be concerned about it attacking any rubber parts in the fuel system like the pump and injector o-rings.
 
#6 ·
My 2004 MDX with 249k miles had the following codes P0171, P2195 and P0420 and was getting poor gas mileage. I replaced the rear cylinder bank pre-cat sensor with an aftermarket sensor, Kwiksen from Amazon. I then cleared the codes. Replacing the sensor got rid of the P0171 and P2195 codes but the P0420 remained.
I wondered if running the car with bad O2 sensor (stuck lean) caused that cylinder bank to run rich and foul the cat.
After reading all the suggestions I decided to add Chevron with Techron to a half tank of premium gas (I always run premium). I drove the car until empty and then cleared the codes. I added another bottle of Chevron with Techron to the empty tank and filled up to half tank. I drove the car for a couple days and then went in for emissions testing and passed.
I'm not sure I really fixed anything but the light hasn't come on since adding this fuel system treatment. I hope this helps.
 
#7 ·
Thanks for the input - it's always helpful to see something that works. I think the scenario you described is likely (bad O2 sensor causing a rich-running condition that "clogged" the cat). I've read other suggestions that just planting your right foot in the carpet (with a long stretch of clear road ahead, and of course, never EVER going faster than the posted speed limit...) the extra heat (lots of it!) will also clear the build-up out of the cat, especially if you do a lot of around-town, low-speed driving.

There are additives that are designed to clean cats, but I can't vouch for any of 'em - I know they didn't work on the Ford I was helping a buddy with, but I've read lots of online reviews where people did seem to have good luck with some of them. You never know, sometimes snake oil can cure a disease! ;-)
 
#8 ·
Rotten egg smell means there is a lot of buildup in the catalysts. Driving hard with premium fuel might help but if you want faster results try seafoam/BK44K:


Temp fix for maybe a month, maybe a few months, maybe years is to use a good cleaning type product like seafoam or BG44K through a vacum intake line for a good clean. Look on youtube for "honda v6 seafoam intake"for and you'll see first hand results.

And/Or

You can add other stuff to gas like some this site recommend:
https://carcaretotal.com/best-catalytic-converter-cleaners/

CRC is a good brand that's popular and available at most auto parts stores.

Best solution:
Get 2 new cats (front and rear) along with new O2 sensors with that high of mileage. It won't be cheap but the car will be running a lot better. OEM is too expensive. New ones are around $500 CAD and come with heat shield each! Pretty costly! But will pass emmissions test.

Other folks cut them out and sell them to scrap places since they have platinum and other good stuff worth $200 dollars!!! Then they put in pipe to eliminate them and put an "o2 bung" to trick the car's computer. It won't pass emmissions that way!
 
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