Car & driving · Free
P0442: small leak in the fuel vapor system (EVAP)
P0442 means the fuel vapor system almost holds pressure, but not quite: the car found a small leak, about the size of a 1 mm hole. Start with the fuel cap seal, then the hoses and valves. The car drives normally.
- No account
- Runs on your device
- Phone & desktop
Check your car for P0442
Runs on your device
Connect your OBD2 adapter
- Plug the adapter into the OBD2 port – usually under the steering wheel, near the pedals.
- Switch the ignition on, or start the engine.
- Bluetooth adapter? Turn Bluetooth on. Nothing else to set up.
This browser cannot talk to OBD adapters. Use Chrome or Edge on Android, Windows or Mac – on iPhone, the free Bluefy browser works with Bluetooth LE adapters. The demo car works everywhere.
Classic Bluetooth adapter (PIN 1234)? Pair it in your system settings first, then choose USB or paired Bluetooth – on a computer or in Chrome 138+ on Android. Wi-Fi adapters cannot work in a browser.
Your car data stays on your device. The page talks to the adapter directly; codes, VIN and values are never uploaded.
Never use it while you drive. Set things up before you set off, or let a passenger handle the phone. Standard OBD2 reads engine and emissions data; ABS, airbag and coding need workshop equipment.
What P0442 means
The EVAP system keeps petrol vapor from the tank inside the car: it stores the vapor in a charcoal canister and lets the engine burn it later. To check the system, the car closes it, builds up a slight vacuum or pressure and watches how fast it disappears.
With P0442 the pressure faded faster than allowed, but not as fast as with a large leak (P0455). The usual reasons are small: a hardened cap seal, a hairline crack in a hose, a valve that does not close completely. They are real leaks of fuel vapor, though, and they rarely fix themselves.
Symptoms of P0442
- In most cases no symptoms besides the check engine light.
- A faint petrol smell near the rear of the car or the filler cap.
- An emissions test that fails because of the stored code or the EVAP self-test.
Causes of P0442, cheapest first
Work down the list in order: the first checks cost little or nothing, the last ones are jobs for a workshop.
A worn fuel cap seal
The rubber ring hardens and cracks over the years. Inspect it, clean the rim of the filler neck and replace the cap if the seal looks tired; it is the cheapest part in the system.
Cracked or loose vapor hoses
Small cracks appear where hoses bend or sit near heat. Check the lines from the tank to the canister and to the purge valve, including clips and quick connectors.
A purge valve that does not seal
The purge valve opens to let the engine draw in the vapor. If it no longer closes completely, the test sees a small leak. It can be tested with a hand vacuum pump.
A leaking vent valve or canister
The vent valve at the canister closes the system for the test. Dirt, spider webs and road salt can stop it from sealing, and the canister housing itself can crack.
Leaks at the tank
Seals at the fuel pump flange or the tank vent lines are the hardest to reach. A smoke test finds them reliably.
Can you drive with P0442?
Safe to drive. P0442 does not affect how the engine runs or how safe the car is. Plan the repair before the next emissions inspection. If you smell liquid fuel rather than a faint vapor, check for a real fuel leak right away.
Check P0442 with OBD Studio
Connect your adapter above, or try the demo car, then:
- Start with the cheap checks, then clear P0442 in Fault codes.
- Drive as usual for a few days: the leak test runs only when the car has stood for some hours and the fuel level is in the middle range.
- In Inspection, the Fuel vapour system (EVAP) monitor turns Complete when the test has passed. If P0442 comes back as a pending code, the leak is still there.
- On cars that report it, Fuel vapour pressure in Live data shows the system pressure while a workshop runs a pressure or smoke test.
More fault code guides
Each of these codes has its own page with causes ranked by cost and the checks that go with them.
- P0420Catalyst efficiency below threshold
- P0171System too lean
- P0300Random or multiple misfire
- P0455EVAP system large leak
- P0128Engine warms up too slowly
- P0172System too rich
- P0401EGR flow too low
- P0101Air flow sensor implausible
- P0135Front O2 sensor heater
- P0016Crankshaft and camshaft out of step
- P0011Intake camshaft timing over-advanced
- P0141Rear O2 sensor heater
- P0113Intake air temperature sensor high
- P0457Fuel cap loose or missing
- P0299Turbo underboost
- P0700Transmission control system fault
- P0087Fuel rail pressure too low
- P0562System voltage low
- U0100Lost communication with engine computer
More OBD Studio pages
Frequently asked questions
Can a fuel cap cause P0442?
Yes, it is one of the most common causes. A cap with a hardened or torn seal lets a little vapor escape, which is exactly what P0442 describes. Replace it if the seal looks worn, then clear the code and give the car a few days.
How do workshops find a small EVAP leak?
With a smoke test: a machine fills the system with harmless smoke at low pressure, and the smoke escapes where the leak is. Cracks you cannot see become visible this way.
Why did P0442 come back after I cleared it?
Clearing only erases the memory. When the car runs its leak test again and the leak is still there, the code returns, usually within a few days of normal driving.
Can I read P0442 without going to a workshop?
Yes. With any ELM327-compatible Bluetooth LE or USB adapter, OBD Studio on this page reads P0442 and every other stored code for free, shows the freeze frame and clears the code after the repair. Nothing to install, no account.
