What P0442 means
The system that captures gasoline vapor from the fuel tank has a small leak. On most cars that's larger than the tiniest leaks (P0456) but far smaller than a missing gas cap (P0455). A worn or loose gas cap is the most common cause, followed by cracked hoses or a valve that doesn't seal.
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. P0442 reports a small leak; what size that means depends on the maker. Ford detects 0.040 in (1 mm) with the engine running: the vent valve closes, engine vacuum pulls the tank down, the purge valve closes and a pressure rise above 2.5 inH2O in 15 s sets the code (0.020 in is P0456). GM uses the natural pressure change after switch-off for 0.020 in and averages several tests. Pump systems at VW and Audi compare against a reference leak. A worn or loose fuel cap is the most common cause.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Check engine light on
- Possibly slight fuel smell
- Readiness or emission inspection not passed
- No change in driving
Common causes
- Fuel cap seal worn, wrong or not clicked in Most likely
- Cracked or porous EVAP hoses or leaking connections Most likely
- Purge or vent valve does not seal Possible
- Leak detection pump itself leaking (VW/Audi) Possible
- Filler neck corroded, tank or sender seal leaking Less likely
How to diagnose P0442
- Check that the gas cap is the correct one for your car, its seal isn't cracked or hardened, and it clicks when tightened. Aftermarket caps don't always seal well.
- Clear the code and drive normally for several days. Some cars only run the leak test after sitting for hours with the engine off, or with the fuel level in a certain range.
- Look at the EVAP hoses you can see near the charcoal canister and fuel tank for cracks or loose fittings.
- If the code returns, have a shop do a smoke test. Small leaks are hard to find by eye.
- Common leak points are the purge and vent valves, the canister, the filler neck seal and, on some cars, the leak detection pump itself.
Vehicles that report P0442 most
| Vehicle | Years | Reports | Share | Median miles |
|---|---|---|---|---|
| Chevrolet Trailblazer | 2003–2004 | 5 | 67k | |
| GMC Envoy | 2003–2004 | 3 | 97k | |
| Chevrolet Corvette | 2009–2013 | 3 | — |
Counts of owner complaints to the NHTSA that mention P0442 (54 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
- 42
- Specific fault
Questions drivers ask
Can I drive with code P0442?
Yes. It doesn't affect how the car runs or its safety. It will likely fail inspection in states that scan the OBD system until it's fixed, and if you smell fuel, have it checked sooner.
Will my car pass an emissions inspection with P0442?
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 P0442 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 P0442 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.
Often reported together
Codes that owners mention in the same NHTSA complaints as P0442. They can point to a shared cause, so it's worth checking them together.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.