P0172 on a Mercedes-Benz: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

You can drive short-term, but the rich mixture wastes fuel and can damage the catalytic converter, so get it checked soon.

What P0172 means on a Mercedes-Benz

On a Mercedes-Benz, P0172 means bank 1 is running rich — too much fuel or not enough air in the mixture. The Mercedes computer has already cut fuel as far as it can and still sees a rich condition, so it stores the code.

Is P0172 common on Mercedes-Benzs?

P0172 is seen on Mercedes models with higher mileage, commonly the C-Class, E-Class, and ML. The MAF sensor is a known trouble spot on many Mercedes engines and can push the mixture rich when it reads high. Aging oxygen sensors and leaking fuel injectors are the other usual causes.

Commonly reported on: C-Class, E-Class, ML, GLK.

Symptoms

Check engine light on
Poor fuel economy
Strong fuel smell from the exhaust
Rough idle

Common causes

most common: Contaminated or failing MAF sensor
common: Aging or faulty oxygen sensor
common: Leaking fuel injector
less common: Faulty fuel pressure regulator holding pressure too high
less common: Restricted air filter or intake

How to fix it

Fix	DIY?	Typical cost
Clean or replace the MAF sensor	Yes	$10–300
Replace the faulty oxygen sensor	Yes	$60–200
Replace leaking fuel injectors or the pressure regulator	Mechanic	$200–600