P0451 on a Mazda: Causes, Fixes & Repair Cost

🟢 Low severity · drivable

You can keep driving a Mazda with P0451 — it's an emissions fault, not an engine problem — but fix it before your next emissions test.

What P0451 means on a Mazda

On a Mazda, P0451 means the fuel tank pressure sensor in the EVAP system is reporting a reading outside the expected range. The sensor monitors fuel vapor pressure in the tank so the computer can run its evaporative emissions test. A bad reading turns on the check engine light but doesn't change how the car drives.

Is P0451 common on Mazdas?

P0451 appears on Mazdas as the fuel tank pressure sensor ages, most often on higher-mileage Mazda3, Mazda6, and CX-5 models. Wiring damage and a sticking vent valve are also common causes. It is an emissions fault, not a drivability fault.

Commonly reported on: Mazda3, Mazda6, CX-5, CX-9.

Symptoms

Check engine light on
Possible faint fuel smell
No change in how the car drives

Common causes

most common: Faulty fuel tank pressure sensor
common: Damaged wiring or loose connector
common: Stuck or faulty EVAP vent valve
less common: Cracked EVAP hose

How to fix it

Fix	DIY?	Typical cost
Inspect the sensor wiring and connector	Yes	$10–50
Replace the fuel tank pressure sensor	Yes	$100–250
Have the EVAP system smoke tested if the code returns	Mechanic	$50–150