Major leak in evap system — usually fuel cap left off.
P0455 — also written PO455, P 0455, 0455 — is the OBD-II code for evap large leak detected. Same code, same fix: this page covers every spelling of it.
EVAP System Large Leak Detected — nine times out of ten it's a fuel cap that wasn't clicked shut at the last fill-up, or the rubber O-ring on the cap has perished. On UK cars 8+ years old the second-biggest cause is a cracked charcoal canister vent hose under the rear arch, usually rotted from road salt. Almost never a genuine fuel tank fault — do NOT let a garage quote you for a new tank without a proper smoke test.
P0455 is a emissions fault code, typically costing £0–£250 to put right in a UK garage.
What P0455 actually feels like to drive
- Engine warning light appears within a mile of filling up — sometimes the cap wasn't clicked shut
- Strong smell of petrol vapour around the car after parking on a hot day
- MPG barely affected — you'll only notice on the fuel receipts over a month
- MOT emissions test passes but the MIL means an MOT visual fail on any car registered 2018+
- Paired codes: P0440 (generic EVAP), P0441 (purge flow), P0446 (vent circuit), P0455 keeps returning
- On Toyota hybrids: MIL flashes then goes steady — hybrid pressurised system is very sensitive
What causes P0455?
- Missing or loose fuel cap
- Disconnected hose
- Damaged tank
UK vehicles that throw P0455 most often
- Ford Fiesta / Focus / Kuga / Transit Connect 1.0 & 1.6 EcoBoost — fuel cap O-ring shrinks
- Vauxhall Corsa D/E / Astra J / Insignia 1.2 / 1.4 / 1.6 petrol — canister purge valve stuck open
- VW Golf / Polo / Audi A3 1.2 / 1.4 / 1.6 TSI & FSI — leaking N80 purge solenoid
- BMW 1 / 3 Series F20/F30 — fuel filler neck seal rots from underneath
- Nissan Qashqai / Juke / Micra 1.2 & 1.6 petrol — split rollover valve on tank
- Toyota Yaris / Auris / Corolla / Prius — hybrid pressurised EVAP triggers P0455 with any tiny leak
- Mini Cooper / Cooper S (R56/F56) 1.6 — well-known charcoal canister cracks
- Kia / Hyundai i10 / i20 / Picanto — fuel cap not sealing after DIY fuel fill-up in wet weather
How P0455 is fixed
- Refit fuel cap
- Inspect hoses
The P0455 misdiagnosis that wastes money
P0455 is where main dealers love to quote £600+ for a new fuel tank or charcoal canister when the actual fault is a £15 fuel cap. Bob's rule: don't authorise ANY EVAP part before a proper smoke test with the tank cap OFF and the smoke machine feeding through the service port. We've seen VW Golfs with three replaced canisters where the real fault was a hairline crack in the plastic filler neck you can only see with the arch liner dropped, and Ford Fiestas where a garage fitted a £280 purge valve when the owner's fuel cap simply wasn't clicking — the ratchet mechanism inside the cap had worn and it felt tight without actually sealing. The other classic miss is on Toyota hybrids: the pressurised EVAP self-test can throw P0455 from a cap seal that would pass on any petrol-only car, so hybrid diagnostics need Toyota Techstream-level coverage not a £30 generic scanner.
What a UK garage should charge for P0455
UK independent garage: EVAP smoke test £45–£80 (this is the ONLY test that finds the leak — insist on it). Genuine or Stant fuel cap £15–£45 fitted. Purge valve / N80 solenoid £70–£160 fitted. Charcoal canister £180–£380 fitted (Mini R56/F56 typically £320+). Filler neck replacement £220–£450 depending on tank drop labour. Leak detection pump (LDP) on VAG cars £140–£240 fitted. Main dealer: budget 50–90% more for the same parts. Never accept a fuel tank quote (£800–£1,600) without written smoke-test evidence — a genuine tank failure on a UK car under 12 years old is rare.
P0455 repair cost in the UK
Most P0455 repairs land between £0–£250 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Bob's tip on P0455
First thing Bob would do — before booking a diagnostic — is drive to a quiet petrol station, remove the cap, wipe the sealing rim clean with a lint-free cloth, refit the cap until it clicks THREE times (twice isn't enough on most cars), and drive 40–60 miles including two cold starts. Around a third of P0455 codes clear themselves this way. If it returns, buy a genuine cap from a factor for £20–£30, never a £6 eBay universal. If it STILL returns after a new cap and 60 miles, book a smoke test — not a generic 'diagnostic'. Ask the garage to write on the invoice which specific component was leaking (fuel cap seal, filler neck, purge valve, canister, LDP, rollover valve) — that paperwork protects you if the code returns, and it stops the classic 'we replaced parts until it went away' £600 bill. Never disconnect the battery to 'reset' P0455 without fixing the cause — modern ECUs re-run the EVAP self-test on the next cold-start drive cycle and the code returns within 20 miles.
Can you drive with P0455?
Drivable.
Urgency: low.