P0174 on a Mercedes-Benz: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

Drivable short-term, but a lean condition on bank 2 should be diagnosed soon to avoid drivability issues.

What P0174 means on a Mercedes-Benz

On a Mercedes-Benz, P0174 means the engine is running lean on bank 2 — the side opposite cylinder 1 — because too much air or too little fuel is getting in. The computer has added as much fuel as it can and still can't balance the mixture. It's the bank 2 version of P0171.

Is P0174 common on Mercedes-Benzs?

P0174 shows up on Mercedes V6 models like the C-Class, E-Class, and ML-Class with the M272 engine family. Intake manifold issues and vacuum leaks are known causes of lean codes on these engines. Cracked intake tubes and dirty MAF sensors are also frequent culprits on higher-mileage Mercedes.

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

Symptoms

Check engine light is on
Rough or surging idle
Hesitation or lack of power
Poor fuel economy

Common causes

most common: Vacuum leak (cracked hose or intake tube)
common: Intake manifold leak or failed runner flap
common: Dirty or failing mass air flow (MAF) sensor
less common: Faulty upstream oxygen sensor (bank 2)
less common: Weak fuel pump or clogged fuel filter

How to fix it

Fix	DIY?	Typical cost
Inspect and repair vacuum leaks (hoses, intake tubes)	Yes	$10–100
Clean the mass air flow sensor with MAF cleaner spray	Yes	$10–20
Have a smoke test performed to find the exact leak	Mechanic	$50–150
Replace a faulty intake manifold or bank 2 oxygen sensor	Mechanic	$200–600

Frequently asked questions

Why is P0174 common on Mercedes V6 engines?

The rubber intake tubes and vacuum hoses on Mercedes V6 engines crack with age and heat. These small air leaks let unmetered air in and set a lean code.

What does bank 2 mean on a Mercedes?

Bank 2 is the side of the engine that does not contain cylinder 1. Only V6 and V8 Mercedes models have a bank 2.

Can I keep driving my Mercedes with P0174?

Short trips are fine, but a lean condition can cause rough idle and hesitation over time. Have it diagnosed soon so a small leak doesn't turn into a bigger repair.