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P0455 Evaporative Emission System Leak Detected (Gross Leak)

A large leak in the fuel vapour system — start with the gas cap, because it genuinely is the answer surprisingly often.

Emissions

The evaporative emission system traps fuel vapour from the tank and feeds it into the engine to be burned instead of vented. The ECU tests it by sealing the system and watching whether it holds pressure or vacuum. P0455 means it lost it fast — a gross leak, roughly the size of a missing gas cap or larger. It never affects how the engine runs, which is why the check-engine light is the only clue you get.

Diagnose P0455 on your specific vehicle Add your year, make and model for ranked causes, repair videos and the exact parts you need

Can I keep driving?

Driveable

Yes, entirely. Just don't expect it to pass an inspection.

How serious

Low. Nothing mechanical is at risk. It fails emissions testing, and you're venting raw fuel vapour to the atmosphere and losing a little fuel to evaporation.

Symptoms you'll notice

What causes P0455

Ordered by what to check first — how likely each cause is, weighed against what it costs to rule out. Working down the list in order is what stops you replacing an expensive part to fix a cheap problem.

01

Loose, damaged or missing gas cap

Check this first, always. A cap not clicked tight after a fill-up is the single most common cause of P0455, and the fix is free. The seal also hardens and cracks with age, so an old cap that looks fine can still leak. Tighten it, drive a few cycles and see whether the light clears before spending anything.

02

Cracked or disconnected EVAP hose

The system runs plastic and rubber lines the length of the car, and they go brittle with heat and age. A gross leak usually means a line has split or popped off a fitting rather than a pinhole.

03

Failed purge valve stuck open

The purge valve should hold the system sealed until the ECU commands it open. One stuck open can't hold vacuum at all, so it reads as a large leak.

04

Failed vent valve

A vent valve stuck open leaves the system permanently open to atmosphere.

05

Damaged charcoal canister

The canister lives underneath the car and takes road debris and corrosion. A cracked one is a straightforward gross leak.

06

Corroded or damaged filler neck

Rust around the filler neck stops the cap sealing no matter how good the cap is. Common on older cars in salted regions.

How to diagnose it

  1. Remove the gas cap, check the rubber seal for cracks and hardening, refit it until it clicks, and drive several trips before doing anything else.
  2. Inspect all visible EVAP hoses along the tank and toward the engine for splits, and check that each is properly seated on its fitting.
  3. Look at the charcoal canister and its lines underneath the car for cracks and corrosion damage.
  4. Check that the purge valve holds vacuum when unpowered — a valve that passes air with no command is stuck open.
  5. A smoke test of the EVAP system is the definitive way to find the leak, and for a gross leak it usually shows up immediately.
  6. Inspect the filler neck for rust that would stop the cap sealing.

Parts you might need

Tools for the job

Related trouble codes

Get the parts list for your vehicle Ranked causes, tutorials and live part prices for your exact year, make and model

Fitment matters. Causes and parts above are the common cases for P0455 across vehicles. The specific part numbers, procedures and torque specs vary by year, make, model and engine — always confirm against service data for your vehicle before buying parts or starting work.