P0451 on a Mercedes-Benz: Causes, Fixes & Repair Cost

🟢 Low severity · drivable

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

What P0451 means on a Mercedes-Benz

On a Mercedes-Benz, P0451 means the fuel tank pressure sensor in the EVAP system is reporting a reading that's outside the expected range. The sensor lets the engine computer monitor fuel vapor pressure in the tank. A bad reading usually turns on the check engine light without affecting how the car drives.

Is P0451 common on Mercedes-Benzs?

P0451 appears on Mercedes-Benz models as the fuel tank pressure sensor ages, often on higher-mileage C-Class and E-Class cars. Access can be tight because the sensor may sit near the fuel tank or the fuel pump module. It is an emissions fault, not a drivability fault.

Commonly reported on: C-Class, E-Class, GLC, GLE.

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 EVAP vent valve
less common: Cracked EVAP line

How to fix it

Fix	DIY?	Typical cost
Inspect the sensor wiring and connector	Yes	$10–60
Replace the fuel tank pressure sensor	Mechanic	$150–400
Have the EVAP system smoke tested if the code returns	Mechanic	$50–150