Small leak in fuel vapour system.
P0442 — also written PO442, P 0442, 0442 — is the OBD-II code for evap system small leak detected. Same code, same fix: this page covers every spelling of it.
EVAP System Small Leak Detected — the little brother of P0455. Same fuel vapour system, just a smaller pinhole. On UK cars it's usually a slightly-worn fuel cap O-ring, a cracked EVAP hose that only leaks when hot, or a purge valve that isn't sealing fully closed. Rarely urgent, never dangerous, but on any 2018+ MOT the illuminated engine light is an automatic fail — so it does need sorting.
P0442 is a emissions fault code, typically costing £15–£250 to put right in a UK garage.
What P0442 actually feels like to drive
- Engine light comes on intermittently, usually 20–60 miles after filling up
- Sometimes clears itself for 200+ miles then reappears — classic pinhole behaviour
- No performance change, no drivability issue, MPG unaffected
- Faint smell of unburnt petrol on a hot day after a long drive
- MOT visual fail on the illuminated MIL — the actual emissions test passes fine
- Paired codes: P0440, P0441, P0446, P0455 may cycle in and out
What causes P0442?
- Loose fuel cap
- Hairline crack in hose
- Failed seal
UK vehicles that throw P0442 most often
- Vauxhall Corsa D / Astra J / Insignia 1.4 & 1.6 petrol — perished EVAP hose behind engine
- Ford Focus / Fiesta / Mondeo 1.6 & 2.0 petrol — canister vent solenoid weep
- VW Golf / Polo / Passat 1.4 & 1.6 FSI — N80 purge valve carbon-clogged and slow to close
- Audi A3 / A4 1.8 & 2.0 TFSI — leak detection pump diaphragm cracks
- BMW 3 & 5 Series N43/N46 petrol — filler neck seal seep once car is 6+ years old
- Toyota Yaris / Auris hybrid — pressurised EVAP amplifies tiny leaks that petrol-only cars would ignore
- Nissan Qashqai / Note 1.6 petrol — rollover valve hairline crack
- Hyundai i10 / i20 / Kia Picanto — cheap aftermarket fuel cap fitted at previous MOT
How P0442 is fixed
- Fuel cap replacement
- Smoke test
The P0442 misdiagnosis that wastes money
P0442 gets misdiagnosed constantly because the leak is by definition tiny — smaller than 0.020" — and only a proper smoke machine set to 6–8 psi will find it. We've seen Ford Focuses where three garages threw a canister, then a purge valve, then a leak detection pump at it, and the real fault was a 5mm split in a rubber vent hose behind the inlet manifold that was only visible with the manifold off. On VAG 1.4 TSI, the N80 purge valve is the single most common cause — a light carbon skim on the valve seat means it doesn't quite close fully, and the tiny bleed reads as P0442. On any Toyota or Lexus hybrid, the pressurised EVAP system is fussy enough that a fuel cap that would pass on a Vauxhall triggers P0442 on a Prius — always check the cap seal condition first.
What a UK garage should charge for P0442
UK independent garage: smoke test with heated evaporative fluid £45–£85 (essential — no other test will find a 0.020" leak). Fuel cap £15–£40 fitted. N80/purge valve £70–£150 fitted (VAG cars). Charcoal canister £180–£380. Small hose replacement £30–£90 depending on access. Leak detection pump £140–£240. Main dealer routinely 40–70% more. On this code specifically, never authorise fuel tank work without written smoke-test evidence — a genuine small tank leak is one in a hundred.
P0442 repair cost in the UK
Most P0442 repairs land between £15–£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 P0442
Two Bob tips that clear P0442 more often than any part swap. One: fill up ONLY to the first click of the pump handle, never top-off. Overfilling floods the charcoal canister with liquid petrol, and the wet canister then throws small-leak codes for months while it dries out. Two: on VAG 1.4/1.6 TSI, ask the garage to CLEAN the N80 purge valve with carb cleaner rather than replace it — around 60% of the time a 10-minute clean and refit clears the code, saving you £100+ on a new valve. If you're getting P0442 on a hybrid, use only manufacturer-approved fuel cap replacements — the Toyota / Lexus cap has a two-stage vent that generic caps do not replicate. And never clear the code and 'see if it comes back' without a smoke test first — you're just delaying the eventual bill.
Can you drive with P0442?
Drivable.
Urgency: low.