P0171 on a Mazda: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

Drivable for a short time, but a lean mixture can cause rough idling and misfires, so get it checked soon.

What P0171 means on a Mazda

On a Mazda, P0171 means bank 1 is running lean, so the engine is getting too much air or not enough fuel. The Mazda engine computer has already added as much fuel as it can and still sees a lean mixture, so it turns on the check engine light.

Is P0171 common on Mazdas?

P0171 shows up on Mazdas with higher mileage, especially the older 2.0L and 2.3L MZR engines in the Mazda3, Mazda6, and MX-5. Cracked intake hoses and vacuum lines are common culprits, along with a dirty MAF sensor. Skyactiv models can see it too when the MAF gets contaminated or a PCV hose cracks.

Commonly reported on: Mazda3, Mazda6, CX-5, MX-5.

Symptoms

Check engine light on
Rough idle
Hesitation or loss of power under acceleration
Poor fuel economy

Common causes

most common: Cracked intake air hose or vacuum line letting in unmetered air
common: Dirty or failing mass air flow (MAF) sensor
common: Clogged PCV valve or hose
less common: Weak fuel pump or clogged fuel filter
less common: Leaking intake manifold gasket

How to fix it

Fix	DIY?	Typical cost
Inspect and replace cracked vacuum or intake hoses	Yes	$10–100
Clean the MAF sensor with MAF cleaner spray	Yes	$10–20
Replace the PCV valve	Yes	$15–50
Replace a weak fuel pump or clogged fuel filter	Mechanic	$300–800