Bank 2 cat efficiency on Mercedes V6/V8 — M272/M273 balance-shaft gear wear or M276 timing chain causing upstream raw fuel.
Mercedes-Benz P0430 — Bank 2 cat efficiency on Mercedes V6/V8 — M272/M273 balance-shaft gear wear or M276 timing chain causing upstream raw fuel. Typical UK independent garage cost: £300–£3200.
What actually causes P0430 on a Mercedes-Benz
On M272/M273 P0430 is famously a downstream symptom of the balance-shaft / idler-gear wear (pre-2008) — once timing slips, raw fuel destroys the bank-2 cat. On M276 it's stretched timing chain and worn guides. Bank 2 on Mercedes V-engines is the passenger side and is buried under heat shields — labour costs are real even before parts.
Mercedes-Benz engines that log P0430
- M272 V6 3.0/3.5 (C/E/SLK)
- M273 V8 5.5 (S/E/CL)
- M276 3.5 V6 direct injection
- M278 4.7 V8 BiTurbo
How we diagnose P0430 on a Mercedes-Benz
- Check VIN against M272/M273 balance-shaft / idler gear service campaign (chassis cut-off ~2008)
- Inspect timing marks through cam cover — wear is visible
- Test rear O2 sensor switching speed
- Pressure-test exhaust upstream of bank 2 cat for cracks
- Borescope M276 valves for carbon before condemning cat
The common misdiagnosis to avoid
Many garages chase O2 sensors and cats on M272 when the actual fault is the balance-shaft gear — only a timing inspection through the cam cover catches it.
Mercedes-Benz P0430 repair cost in the UK
Expect £300–£3200 including parts and labour at an independent garage. Main-dealer quotes on Mercedes-Benz are usually higher for the same job, and the spread exists because the cheap cause and the expensive cause throw the same code — pay for the diagnosis before you pay for parts.
Service campaign / TSB note
Mercedes M272/M273 balance shaft / idler gear service campaign covers 2005-2008 production.
Bob's workshop tip
M272 P0430 — always pull the cam cover before the cat. A £1,200 balance-shaft job is bad news but quieter than a £3k cat that fails again in 8 weeks.
Codes usually seen alongside P0430 on Mercedes-Benz
- P0420
- P0017
- P0016
Symptoms drivers report with P0430
- MIL comes on after a motorway run then stays lit — no drivability change
- Slight sulphur/rotten-egg smell on hard acceleration
- MPG drop of 1–3 mpg you wouldn't notice unless you track it
- Fails emissions/lambda snapshot at MOT despite passing tailpipe CO
- Bank 2 short-term fuel trim slightly richer than bank 1 at cruise
Repairs that clear P0430
- Same diagnostic as P0420 but bank 2 side
- Replace bank 2 rear lambda first as trial
- Confirm with lambda graphing before cat replacement
For the generic, all-makes explanation of this code — meaning, every known cause and UK cost bands — see our P0430 guide.
Reading P0430 on a Mercedes-Benz properly
A generic reader will show P0430 and nothing else. What matters is the freeze-frame data stored with it — engine speed, load, coolant temperature and fuel trims at the moment the fault was logged — plus whether any other module on the Mercedes-Benz has logged something at the same time. Codes rarely arrive alone, and the order they were stored in usually points at which one is the cause and which are the consequences.
Clearing P0430 without fixing it
Erasing the code resets the Mercedes-Benz's readiness monitors as well as the light. The fault returns on the next drive cycle if the cause is still there, and in the meantime the incomplete monitors can stop the car passing an emissions check. After a genuine repair, the car is driven until the relevant monitor completes before it is handed back.
Bob's Mechanical Repairs is an independent garage in Birnam, Dunkeld, Perthshire, with 32 years of Bob's experience on the tools. If P0430 is showing on your Mercedes-Benz, bring any scan results with you — we will read the live data ourselves, confirm which cause it actually is, and price the repair before any work starts.