Mercedes-Benz P0171

System too lean on Mercedes — M271 1.8 Kompressor and M274 2.0 turbo both have a signature intake manifold runner / PCV issue.

Mercedes-Benz 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 independent garage cost: £160–£620.

What actually causes P0171 on a Mercedes-Benz

On the M271 1.8 Kompressor the inlet manifold tumble flaps fail and the engine pulls unmetered air, throwing P0171 alongside flap codes (P2004 series). On the M274 2.0 turbo the camshaft adjuster magnets and the cam cover PCV system are common lean-code causes. M276 V6 is typically a split or perished crankcase breather hose at the back of the engine.

Mercedes-Benz engines that log P0171

• M271 1.8 Kompressor (C180/C200, E200)
• M274 2.0 turbo (C200/C250, E200/E250, GLC200)
• M276 V6 3.0/3.5 (E350, GLE350)
• OM651 2.1 diesel (intake-related)

How we diagnose P0171 on a Mercedes-Benz

1. XENTRY / generic scan — read trims, manifold pressure deviation, and any P2004 series flap codes
2. Smoke-test intake — focus on the rear of the engine on M276 V6 (hidden breather)
3. Inspect intake manifold runner motor (M271) — listen for failed motor on key-on test
4. Check PCV / oil separator on cam cover for cracks (M274)
5. On OM651 diesel, output-test intake flap actuator before condemning manifold

The common misdiagnosis to avoid

Mercedes specialists in the UK routinely quote full intake manifold replacement (£900+) on M271 when the actuator alone is the failed item. Get a second opinion — actuator-only repair is £180–£280 at an indie.

Mercedes-Benz P0171 repair cost in the UK

Expect £160–£620 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.

Bob's workshop tip

On the M271 Kompressor, if you've got P0171 with the manifold flap codes, replace the actuator alone first — the manifold itself almost never fails. Saves £700+ over the dealer route.

Codes usually seen alongside P0171 on Mercedes-Benz

• P0174
• P2004
• P2006

Symptoms drivers report with P0171

• Hesitation or 'flat spot' pulling away from junctions and roundabouts when engine is warm
• Rough or lumpy idle, worse when air-con clicks in (extra load exposes the lean condition)
• Occasional cough or backfire through the intake when accelerating hard from low RPM
• MPG dropping 3–8 mpg over the last month with no change in driving style
• Faint hissing under the bonnet at idle (vacuum leak from cracked manifold or split hose)
• Paired codes: P0174 (bank 2 lean, V6/V8 only), P0507 (idle too high), P2187 (idle lean), P0300-series misfires

Repairs that clear P0171

• Smoke-test for vacuum leaks
• Clean MAF sensor with proper cleaner
• Test fuel pressure
• Replace fuel filter
• Replace failed sensor

For the generic, all-makes explanation of this code — meaning, every known cause and UK cost bands — see our P0171 guide.