P0420 Check Engine Light
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Newbie
Joined: Mar 2019
Posts: 6
Likes: 5
ML 350
P0420 Check Engine Light
Have a 2013 ML350 3.5L V6 4Matic with 187,000 miles on it. Had a P0420 Catalytic Converter 1 light come up. Cleaned the O2 sensors, and light was gone for about a thousand miles. P0420 came back on right at around 850 miles.
Verified no misfiring, no oil leaks, and sensors look good. Anyone aware of any work around? Oddly enough, had to do an emissions test for a state inspection 200 miles before the light came back on, and they verified exhaust is clean and no issue.
any guidance would be greatly appreciated!
Verified no misfiring, no oil leaks, and sensors look good. Anyone aware of any work around? Oddly enough, had to do an emissions test for a state inspection 200 miles before the light came back on, and they verified exhaust is clean and no issue.
any guidance would be greatly appreciated!
Out Of Control!!
Joined: Apr 2019
Posts: 11,924
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
Have a 2013 ML350 3.5L V6 4Matic with 187,000 miles on it. Had a P0420 Catalytic Converter 1 light come up. Cleaned the O2 sensors, and light was gone for about a thousand miles. P0420 came back on right at around 850 miles.
Verified no misfiring, no oil leaks, and sensors look good. Anyone aware of any work around? Oddly enough, had to do an emissions test for a state inspection 200 miles before the light came back on, and they verified exhaust is clean and no issue.
any guidance would be greatly appreciated!
Verified no misfiring, no oil leaks, and sensors look good. Anyone aware of any work around? Oddly enough, had to do an emissions test for a state inspection 200 miles before the light came back on, and they verified exhaust is clean and no issue.
any guidance would be greatly appreciated!
MBWorld Fanatic!
Joined: Jan 2016
Posts: 2,749
Likes: 880
From: In the Shadow of the Tetons
2013 ML350 Bluetec
https://www.subaruoutback.org/thread...agnosis.49537/
Sure it's on a Subaru forum but the principles are the same. Cardoc knows his $h!+.
Sure it's on a Subaru forum but the principles are the same. Cardoc knows his $h!+.
Out Of Control!!
Joined: Apr 2019
Posts: 11,924
Likes: 6,776
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
The other bank side is ok!
In fact you'll want to compare one side against the other.
Read your LTFT at warm idle.
This will show you why half your engine is acting up.
The long story short is don't focus on the cat inability to scrub rich mixtures. Focus on the causes...
Last edited by CaliBenzDriver; Sep 8, 2025 at 02:00 PM.
