P0420 Catalytic converter code - MBWorld.org Forums

May 20, 2025 | 07:27 AM

sn202020

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Joined: Jan 2020

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From: Canada

2017 & 2022 GLC 300 4Matic

P0420 Catalytic converter code

I've seen this code and CEL for months at my 2017 GLC300,

P0420 [0x0420] Catalytic converter system, bank 1 -efficiency below threshold

Finally installed the adapter into the 2nd o2 sensor(under the engine air filter housing), which will reduce the sensing ability by the longer distance, and mimic the cat working better.

and it cleared the CEL right after I start engine. Not bad. $5 adapter from AliE.

Last edited by sn202020; May 20, 2025 at 07:28 AM.

May 20, 2025 | 08:00 PM

sn202020

Thread Starter

Member

Joined: Jan 2020

Posts: 210

Likes: 79

From: Canada

2017 & 2022 GLC 300 4Matic

P0420 is gone, but got another one.

P013F Heated oxygen sensor (HO2S) 2, bank 1 - delayed response lean to richStatus: Pending

Maybe too long adapter.

Aug 26, 2025 | 01:13 AM

sn202020

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Member

Joined: Jan 2020

Posts: 210

Likes: 79

From: Canada

2017 & 2022 GLC 300 4Matic

Just to update.

P0420 (Cat efficiency) then after the adapter, got P2187 (too lean at idle) until today.

Finally I bought the downstream O2 sensor A0075426418 from Ali under $30 and installed without the adapter.
No more any codes. All good now.

I looked at the O2 sensor hole, and the cat looks all clean good.

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