P0171 on a Mercedes-Benz: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

A Mercedes-Benz with P0171 is drivable short-term, but a lean mixture can cause misfires and should be fixed soon.

What P0171 means on a Mercedes-Benz

On a Mercedes-Benz, P0171 means bank 1 is running lean — too much air or not enough fuel — and the engine computer has reached its limit correcting it. The computer uses the MAF sensor and oxygen sensors to judge the mix, and a persistent lean reading sets P0171.

Is P0171 common on Mercedes-Benzs?

P0171 shows up on higher-mileage C-Class, E-Class, and S-Class models. Mercedes engines commonly develop vacuum leaks in crankcase ventilation hoses and intake boots, and a failing MAF sensor is also a known cause.

Commonly reported on: C-Class, E-Class, S-Class, GLE.

Symptoms

Check engine light on
Rough idle
Hesitation under acceleration
Worse fuel economy

Common causes

most common: Vacuum leak (crankcase ventilation, intake boot)
common: Dirty or failing MAF sensor
common: Faulty PCV valve
less common: Weak fuel pump or clogged fuel filter

How to fix it

Fix	DIY?	Typical cost
Inspect and replace cracked vacuum and crankcase hoses	Yes	$20–250
Clean the MAF sensor with MAF cleaner	Yes	$10–20
Replace the PCV valve	Mechanic	$100–450
Replace a weak fuel pump or clogged fuel filter	Mechanic	$400–1000