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Cleaning the catalytic converter
NOTE: In most cases, it is not possible to clean the catalytic converter to get rid of the P0420 code. In most cases, it has to be replaced, along with the oxygen sensors. In some cases, you can TEMPORARILY get rid of the P0420 error if it came on recently by taking the catalytic converter off your car, and cleaning it gently with compressed air, and cleaning/replacing the oxygen sensor. Do not listen to online advice about adding thinner, or any other liquid to your gas tank. That will never clean your catalytic converter. NOTE: you will also get decreased engine performance anyways with clogged up oxygen and MAF sensors. It is still necessary to clean or replace all of these parts to have the engine operating at peak performance. There are no magic cures to the failing / old catalytic converter. You will need to replace it sooner than later. You may save money by finding an EXACT OEM complete catalytic converter or one you can have welded to your exhaust system, BUT IT MUST BE EXACT SIZE AND SHAPE.
After I have replaced the oxygen sensors, which were covered with soot and other deposits, the car no longer misfired on the highway. It did, however, throw up the dreaded "Catalytic converter below optimum efficiency" code.
I went online to see how much a generic replacement and whether it can be cleaned.
First of all, stay away from generic catalytic converters which must be welded by you into the old pipe. They list generic crap online which will never fit because of length, angle, and several other factors. For example, this is a picture of mine catalytic converter:
There's no way a welder can cut it out and weld a new one to those pipe ends at these angles.
Second bit of information: unless you are patient and/or know what you are doing, do not attempt to take the catalytic converter off the car. It is nearly impossible to access the bolts. I had to use some very weird socket extensions, have two people, et cetera. And all manuals and online advice stated dryly "take the catalytic converter off the car". Those people have no idea you have no access with the engine on.
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Page last modified 12-Dec-12 22:09:54 EST
Comments on this page:
Comment: I'm having issues with my Thunderbird LX v8 4.6L it smells like rotten eggs so I'm told it is the catalytic converter. I would give it gas past 1 rpm then once off the accelerator she wouldn't keep running. I've had trouble with this car since the day I bought her. A lemon if you will. Anyhow, can anyone give me any pointers on how cheap I can find one. I also know it has been misfiring for as long as I know. I've replaced water pump and used motor which was a LTD motor and the spark pugs were not replaced nor was the wires. Hey I'm a chick that doesn't know much about vehicles.
Comment: Don't use a universal? Don't take the cat off? How do I clean it if you advise me to never take the cat off because I would be insane to do so? The article about cleaning is helpful, but the rest doesn't make a lot of sense. A universal will fit many cars just fine. Maybe not yours.
Comment: <p><span style="font-size: small;">First of all, please excuse my grammar or English, English is my second language. I am glad that you said the thinner is nuts! When I read on another forums about to put the thinner in gas tank and it will clean the catalytic converter, I am like WTH? Anyway, I know you are talking about the Audi, I couldn't find any more information about Honda without the word "thinner" from moron. I am 1998 Honda Accord 3.0 owner, and it has 201,000 miles right now. The auto scanner device shows the code: P0420 and P1456, so I want to focus on P0420 first. The question is, I am not sure which issue my car has: oxygen sensor or catalytic converter. Should I replace the new oxygen sensor first since it is way cheaper than OEM catalytic converter, or should I clean a little bit inside the catalytic converter (as you describe and show the pictures to us) before I buy the new oxygen sensor ($68.99) and catalytic converter ($799.95)? Thank you for your time.</span></p>
Comment: <p>In most modern car's the exhaust bolts aren't the easiest to get to, they're often at funny angles which require a little bit of thought and some perseverance to get to and crack off. I have removed hundreds of cat's and never needed the resources that you described to remove one.</p> <p>And on the generic catalyst subject, yes, on occasion bends are required, these can be either fabricated with an angle grinder / welder, or pipe bender if you want to be professional about it, or simply weld in bends from old exhaust pipe. These procedures are not that complicated. If you can't operate an angle grinder then it's probably best that you don't try welding.</p> <p>The cat in the picture is melted / face plugged, this cat should be replaced, the overtemperature has damaged the substrate and could cause it to break up and become lodged in the exhaust during engine operation.</p> <p>In answer to the question about the complexity of a cat, the mesh that you see is a ceramic brick, this is the expensive part, they aren't mechanically complicated, they're expensive because the wash coat applied to the substrate uses expensive precious metals and procedures.</p> <p>To be honest though, if you couldn't remove the exhaust on your own you probably should have stopped there and taken it to someone with more than 3 spanners in their toolbox.</p>
Hmmm... I've never seen the inside of a Cat, but since they're so expensive, somehow I think it's reasonable to assume that the insides must consist of more than just the simple screen as shown in your picture. Your problem would seem to have been with the clogged (and easily scraped) screen, but what if the insides (which are inaccessible) were clogged up too? I mean, I'd really hate to have gone to all the trouble (of removing and reinstalling it) for nothing... Would washing it out with gasoline, or maybe some engine degreaser help too? BTW, good point about the "parrots".
Editor's response: The procedure described above only applies to cats which were melted from the hot exhaust, perhaps from the engine running rich for an extended amount of time. You cannot wash a catalytic converter with anything, be it gasoline, degreaser, carb cleaner, etc.