P0174 on a BMW: 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 BMW

On a BMW, 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 BMWs?

P0174 is a very common code on BMW inline-6 engines in the 3 Series, 5 Series, X3, and X5. Crankcase ventilation (PCV) system failures and cracked intake boots are classic BMW lean-code causes. Vacuum leaks from aging hoses and a dirty MAF sensor also show up often as these cars pass 100,000 miles.

Commonly reported on: 3 Series, 5 Series, X3, X5.

Symptoms

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

Common causes

most common: Crankcase ventilation (PCV) system failure
common: Cracked or disconnected intake boot
common: Vacuum leak (cracked hose or gasket)
common: Dirty or failing mass air flow (MAF) sensor
less common: Faulty upstream oxygen sensor (bank 2)

How to fix it

Fix	DIY?	Typical cost
Inspect and replace the crankcase ventilation valve and hoses	Yes	$50–200
Replace a cracked intake boot	Yes	$30–100
Clean the mass air flow sensor with MAF cleaner spray	Yes	$10–20
Have a smoke test performed to find the exact vacuum leak	Mechanic	$50–150

Frequently asked questions

Why is P0174 so common on BMW inline-6 engines?

The crankcase ventilation system on BMW inline-6 engines fails with age, and the rubber intake boots crack. Both let unmetered air in and cause a lean condition.

What does bank 2 mean on a BMW?

Bank 2 is the side of the engine that does not contain cylinder 1. On BMW inline-6 engines, bank 2 is the rear of the engine, opposite cylinder 1 up front.

Can I keep driving my BMW 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.