How to fix the issues with trouble code P0420? (2024)

#1

How to fix the issues with trouble code P0420?

Hello,
I have a old Mercedes ML550 (2009) with over 150k miles on it. Last week, Chkengine light came on with a code P0420. Looks like the catalistic converter is bad, probably because of the high mileage.
Here are my options:
1) use C.C. cleaner ;
2) remove the C.C. and clean the inside with hi pressure water gun;
3) replace the C.C. with an aftermarket one.
Any recommendation is welcome.
Thanks in advance.

#2

P0420 can also be caused by faulty oxygen sensor, exhaust system leak, or intake leak. Don't know much about CC cleaners, but I doubt they work. You need to make sure what the issue is that is causing the code.

#3

#4

would likely just buy an aftermarket converter.

#5

Since a P0420 code is not a series problem and usually doesn't affect performance very much, I would be reluctant to start swapping parts and throwing money at it. It very well could be a bad converter, but before I spent that kind of money, I would try some diagnostics. There are a couple of different ways you can test converters and I would want to do that first. I would also be very careful about aftermarket converters. There are some good ones out there, but there are also some really bad ones. Do your homework and research before spending that kind of money.

#6

#7

Don't know anything about washing converters. I guess if the guts of the converter is covered would carbon then cleaning it might help, But I would assume that if the converter got that foiled up, it's not doing is job properly and would need to be replaced.

#8

#9

Thanks Dixie2012, Alan73 and Whittsend for all your tips. I will keep you posted about what happens.

depends on your states inspection requirements but you probably need to try another scan tool to clear the codes with, often this code may not return very quickly may take a week or so of driving it so it may be possible to clear it and get it inspected and the light be off if that is all they check for in the most basic inspections states there more concerned about brakes, suspension, and steering but the more emissions related inspections will likely analyze the exhaust and it would need to pass and they likely hook a scanner and see the codes was cleared recently.

I had the same code on a different vehicle. The code just went away after a few tanks of gas. Code never came back.

Most codes only require one instance of an abnormal reading to be set off but can take anywhere from a few to 40 or more stop/start cycles of the engine, without the ECM seeing the same abnormal reading before they clear. The few tanks of gas may have had nothing to do with it.
It only takes one faulty reading to set the code, but lots of no faulty for them to clear themselves. It may have been the gas or it may have been the cycles.