What Mercedes-Benz codes (P0299, P2002, P0420, P0401, P0203, P0106) actually mean on Mercedes-Benz engines — the real cause, the common misdiagnosis, and the honest UK repair cost.
These are the OBD fault codes we see most often on Mercedes-Benz vehicles in the workshop, with the real cause on Mercedes-Benz engines rather than the generic textbook definition, plus the honest independent-garage cost.
Mercedes-Benz fault codes explained
- P0299 — Turbo underboost on Mercedes — on 2.1 OM651 diesel it's the boost pressure sensor or charge air pipework; on M271 petrol it's the supercharger or chain. Typical UK cost £180–£2200.
- P2002 — DPF efficiency on Mercedes diesels — OM651 and OM642 engines suffer carbon-blocked EGR cooler that fouls the DPF prematurely. Typical UK cost £280–£2400.
- P0420 — Catalyst efficiency on Mercedes petrol — on M271 1.8 Kompressor, the supercharger oil seal failures fouls the cat. On M276 V6, lambda sensor drift is more common. Typical UK cost £180–£1400.
- P0401 — EGR flow insufficient on Mercedes OM651/OM642/OM646 diesels — typically a stuck EGR valve or cooler clogging on city-driven C/E/Sprinter. Typical UK cost £260–£1100.
- P0203 — Injector circuit Cylinder 3 on Mercedes — OM651/OM642 piezo injectors and OM611/OM646 Delphi units both fail with mileage; cyl 3 often singled out by harness routing. Typical UK cost £380–£1300.
- P0106 — MAP sensor performance on Mercedes — OM651 diesel boost sensor and M271/M274 petrol intake sensors both fail with mileage. Typical UK cost £140–£480.
- P0562 — System voltage low on Mercedes — alternator failure and dual-battery system issues on S/E/GL with second battery. Typical UK cost £180–£720.
- P0100 — MAF circuit malfunction on Mercedes — OM651 diesel MAF and M271/M272/M276 petrol MAF all fail with mileage and EGR contamination. Typical UK cost £160–£520.
- P0304 — Cylinder 4 misfire on Mercedes — M271 Kompressor and M274 turbo petrol coil failure, OM651 diesel injector or glow plug. Typical UK cost £160–£720.
- P0171 — System too lean on Mercedes — M271 1.8 Kompressor and M274 2.0 turbo both have a signature intake manifold runner / PCV issue. Typical UK cost £160–£620.
- P0301 — Cylinder 1 misfire on Mercedes — M271/M272/M274 coil packs, injectors and timing chain wear are the headline causes. Typical UK cost £100–£1800.
- P0410 — Secondary air injection malfunction on Mercedes — M271 Kompressor SAI pump is the textbook UK failure. Typical UK cost £250–£1400.
- P0193 — Fuel rail pressure sensor high on Mercedes — OM651/OM642 CDI rail sensor failures, sometimes CP4 related. Typical UK cost £180–£1200.
- 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 cost £300–£3200.
- P0087 — Fuel rail pressure too low on Mercedes OM651/OM642 diesel — HP pump shaft wear (Bosch CP4) and fuel contamination. Typical UK cost £600–£6000.
- P0011 — VVT 'A' over-advanced Bank 1 on Mercedes — M271 magnet adjuster failure and M276 chain stretch. Typical UK cost £140–£2400.
- P0016 — Crank/cam correlation Bank 1 on Mercedes — M271 chain stretch (single-cam) and M276 stretched chain. Typical UK cost £600–£2600.
- P0089 — Fuel pressure regulator on Mercedes — OM651/OM642 DRV and CP4 pump regulator failure. Typical UK cost £250–£6000.
- P0234 — Turbo overboost on Mercedes — OM651 BiTurbo low-pressure actuator and M274 wastegate stick. Typical UK cost £240–£1600.
- P0507 — Idle speed higher than expected on Mercedes — M271/M274/M276 PCV diaphragm and vacuum hose. Typical UK cost £180–£580.
- P2463 — DPF soot accumulation on Mercedes — OM651 / OM642 DPF over-soot from failed regens. Typical UK cost £180–£2400.
- P0341 — Camshaft position sensor performance on Mercedes — M271/M272/M274 sensor failure with intermittent stall. Typical UK cost £140–£420.
Codes are generic across manufacturers, but the fix is not. The same code on a Mercedes-Benz usually points at a different component than it would on another make, which is why a make-specific diagnosis saves money before any parts are bought.