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2018 Mercedes-AMG C63 — catalyst efficiency code but car drives normally

TowMechanicish155Community StarterFeb 27, 20262018 Mercedes-AMG C63 SSan Diego
2018 Mercedes-AMG C63 S, about 79,000 miles. A catalyst efficiency code came back after clearing once. The car drives normally and there are no misfire codes. Before condemning the catalytic converter, what sensor/data checks are worth doing?
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3 replies

TrailDaily11Community StarterCommunity StarterFeb 27, 2026permalink
Ask what changed right before it started. Loaded-suspension checks on the 2018 Mercedes-AMG C63 catch play that a wheels-hanging inspection misses. If the cheap test changes it, stop and reassess. Do that first. That's coming from doing this as an owner, not a shop. Not driving it hard until I know more.
TowMechanicish155Community StarterCommunity StarterFeb 28, 2026permalink
Checked the easy stuff on the 2018 Mercedes-AMG C63 and found one clue worth chasing before I book a shop. This is the version I'd tell a friend.
UsedCarDaily840Community StarterCommunity StarterMar 1, 2026permalink
I'd push back a little: Swap the cheap/easy piece first on the 2018 Mercedes-AMG C63 and see if the fault moves. You'll know quickly if you're on the wrong tree. Write the result down so the next test isn't a repeat of the last one. I refuse to clear codes until someone else sees them.
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