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.

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

1. Check VIN against M272/M273 balance-shaft / idler gear service campaign (chassis cut-off ~2008)
2. Inspect timing marks through cam cover — wear is visible
3. Test rear O2 sensor switching speed
4. Pressure-test exhaust upstream of bank 2 cat for cracks
5. 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.