P0174 on a Mazda: 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 Mazda

On a Mazda, 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 Mazdas?

P0174 shows up on Mazda V6 models like the CX-9, since only V6 Mazdas have a bank 2. Vacuum leaks from cracked hoses and intake gaskets are the usual causes on these engines. A dirty MAF sensor and a weak fuel pump are also frequent culprits on higher-mileage Mazdas.

Commonly reported on: CX-9, Mazda6, CX-7.

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 gasket)
common: Dirty or failing mass air flow (MAF) sensor
common: Intake air leak after the 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, gaskets)	Yes	$10–100
Clean the mass air flow sensor with MAF cleaner spray	Yes	$10–20
Replace the bank 2 upstream oxygen sensor if it's reading wrong	Yes	$60–200
Have a smoke test performed to find the exact leak	Mechanic	$50–150

Frequently asked questions

Why is P0174 common on Mazda V6 engines?

The rubber vacuum hoses and intake gaskets on Mazda V6 engines can leak air as they age. A small leak on bank 2 is enough to set the code.

What does bank 2 mean on a Mazda?

Bank 2 is the side of the engine that does not contain cylinder 1. Only V6 Mazdas like the CX-9 have a bank 2, so 4-cylinder models won't set P0174.

Can I keep driving my Mazda 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.