P0455 Code: Meaning, Causes and Repair Cost

The system that traps gasoline vapor from the fuel tank has a large leak, or it can't build up any vacuum at all. The most likely reason is simple: the gas cap is missing, loose or not clicked in. A disconnected or cracked hose or a stuck valve can also cause it.

How the engine computer detects it

The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. P0455 means a large leak or that no vacuum builds up. Ford pulls the closed system down with engine vacuum and expects about −2 kPa (−0.3 psi) within 30 s; after refuelling it sets P0457 instead. GM sets the code if 20 liters have been purged without reaching 2740 Pa tank vacuum (once per cold start, MIL after two trips). Saab's ME9 uses a pressure drop below 525 Pa. The code also covers blocked purging, for example a purge valve stuck closed.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

Check engine light on (possibly a check fuel cap message)
Possibly fuel smell
EVAP readiness or emission inspection not passed

Common causes

Fuel cap missing, not clicked in or seal faulty (or capless flap) Most likely
Hose off or cracked (canister, filler neck, purge line) Most likely
Vent valve stuck open or purge valve stuck closed Possible
Canister or filler neck cracked or corroded Possible

How to diagnose P0455

Make sure the gas cap is there, clicked in and has an intact seal. On a capless filler, check that the flap closes fully. A cap left off after refueling is a classic cause.
After fixing the cap, clear the code or wait. The car has to rerun the leak test over several drives before the light goes off.
Look under the car near the fuel tank and charcoal canister for a hose that has come off or cracked, and check the filler neck for rust.
This code also sets if the system can't pull vacuum, for example with a purge valve stuck closed or a vent valve stuck open. A shop can operate both valves with a scanner.
If nothing obvious turns up, a smoke test of the EVAP system will find the leak.

Vehicles that report P0455 most

Vehicle	Years	Reports	Median miles
GMC Envoy	2003–2004	4	110k
Ford Fusion	2010–2011	4	77k
Kia Soul	2015–2018	4	—
Chevrolet Trailblazer	2004	3	128k
Jeep Grand Cherokee	1997–2004	3	87k
Ford Escape	2005–2011	3	—

Counts of owner complaints to the NHTSA that mention P0455 (73 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.

Reading the code

P: Powertrain
0: Generic (SAE) code
4: Auxiliary emission controls
55: Specific fault

Questions drivers ask

Can I drive with code P0455?

Yes, it doesn't change how the car drives. Fix it soon, though: it will likely fail inspection in states that scan the OBD system. If you smell raw gasoline or see fuel dripping, don't drive; have it checked for a fuel leak.

Will my car pass an emissions inspection with P0455?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Will P0455 clear by itself?

The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.

Can I fix P0455 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: easy. Start with the cheapest checks before replacing expensive parts.

Often reported together

Codes that owners mention in the same NHTSA complaints as P0455. They can point to a shared cause, so it's worth checking them together.

P0455 EVAP System Leak Detected - Large Leak

What P0455 means