What does code P0442 mean?
Short answer
P0442 means the evaporative emissions (EVAP) system, which holds gasoline vapor from the tank, found a small leak. Rick's Free Auto Repair Advice calls a loose or faulty gas cap by far the most common cause, followed by cracked EVAP hoses and a purge or vent valve that doesn't seal fully.
Safety first. Edmunds says the car is safe to drive with P0442, but get it fixed soon because the leak can grow and it will fail an emissions test in states that require one. If you smell strong fuel, don't wait.
On this page
Step by step
- 1
Check and tighten the gas cap
Tighten it until it clicks, and look at the rubber seal for cracks or flattening. A cap that's old or doesn't seal is a cheap first fix.
- 2
Let the system retest
The light won't go off the moment you tighten the cap. The car has to rerun its leak test, which happens on its own schedule over the next few drives, and pass it.
- 3
Inspect hoses and the filler neck
Look at the EVAP hoses you can reach and the fuel filler neck for dry rot, cracks or rust. Small leaks hide well, so not finding one doesn't mean there isn't one.
- 4
Smoke test it
A smoke test is the most effective way to find small leaks. Smoke goes into the EVAP system through its service port and shows up wherever it escapes. Shops do this; some parts stores rent smoke machines.
- 5
Check the purge and vent valves
A valve that doesn't close all the way leaks vacuum just like a hole. A shop can command each valve with a scan tool and check that it seals.
How the car finds a small leak
The EVAP system keeps gasoline vapor sealed in, stores it in a charcoal canister, and later burns it in the engine. To make sure the system is sealed, the engine computer tests it. Rick’s Free Auto Repair Advice explains that many cars pull a vacuum on the whole fuel system and watch how fast it fades: if it can’t hold vacuum, even through a pinhole, P0442 sets. Some Chrysler vehicles use a different method that watches natural pressure changes as the fuel warms and cools.
Common causes
| Part | What goes wrong |
|---|---|
| Gas cap | Loose, or the rubber seal is worn or cracked. The most frequent cause. |
| EVAP hoses | Dry-rotted or cracked |
| Purge or vent valve | Doesn’t seal all the way |
| Filler neck | Rusted, corroded or leaking |
| Charcoal canister | Cracked |
| Fuel tank pressure sensor | Faulty or reading wrong (less common) |
What you’ll notice
Usually nothing but the check engine light. Edmunds and O’Reilly both mention a possible fuel smell.
When to see a pro
Tightening or replacing the gas cap is DIY. If the code returns, the leak is small and hard to find by eye, so a smoke test at a shop is usually the fastest route to the real cause.
Common follow-up questions
What's the difference between P0442 and P0455?
Both come from the same EVAP leak test. P0442 is a small leak and P0455 is a large one; Edmunds defines the P0455 threshold as equal to a hole about 0.04 inch across or larger. P0456 is a very small leak. The likely causes overlap a lot, and the gas cap is the first check for all three.
Can I drive with a P0442 code?
Yes. Edmunds says the car is safe to drive, and O'Reilly says you probably won't notice any performance problems. Fix it soon anyway, since emissions go up, the leak can get worse, and you'll fail a required emissions test.
Will a new gas cap fix P0442?
Often, but not always. A loose or worn cap is the most frequent cause, so it's the cheap first try. If the code comes back after the system has rerun its test, the leak is somewhere else and a smoke test is the next step.
Why did P0442 show up right after I got gas?
The most likely reason is the cap wasn't tightened fully. Rick's Free Auto Repair Advice also notes many systems start a leak test after they see the fuel level rise from a fill-up, so a refuel is exactly when a leak gets caught.
Does P0442 affect gas mileage?
Slightly, if at all. Edmunds lists a small drop in fuel economy and a fuel smell as possible symptoms, but most cars show nothing but the check engine light.
Sources
- 1.Edmunds: What does the P0442 error code mean?
- 2.Rick's Free Auto Repair Advice: P0442 code causes and fixes
- 3.O'Reilly Auto Parts: Check engine light code P0442, small EVAP leak
General information only, not a diagnosis. Your owner’s manual comes first. How we write these