P0442 Code

The gas in the tank is always releasing fumes. Instead of releasing them into the air, your car holds on to them and burns them in the engine later. The parts that catch and store these fumes form the EVAP system, which stands for evaporative emission system. Now and then the car's computer runs a leak test on these parts. If there is a small leak, the computer records code P0442 and lights the check engine light (the orange engine-shaped light on the dashboard).

Two parts cause nearly every small leak, and luckily the cheaper one is the usual cause:

• the gas cap, which closes the opening where you fill up
• EVAP purge valve, the small valve by the engine that lets stored fumes enter the engine for burning

According to Edmunds' P0442 page, you can keep driving while you find the cause.

The gas cap comes first. Checking costs nothing, and it's often the entire fix.

1. Take a look at the cap. The cap should sit straight, and the rubber seal should be clean and free of cracks.
2. Turn the cap until you hear it click, then keep driving normally. RepairPal recommends trying this before buying a new cap, since the code can come from nothing more than a loose cap. It may take a few days for the light to go off, since the car has to repeat its own leak test.
3. Check under the car by the gas tank if you hit something on the road recently, or if the hoses might have been chewed by animals. Carparts.com notes this damage is often easy to spot.
4. Get a new gas cap if the old one is damaged or the light returns.
5. When a replacement cap still doesn't solve it, pay a shop to find the problem (this is called a diagnosis). The shop's EVAP test shows exactly where the leak is, so you only pay for parts the car actually needs.
6. If testing shows the purge valve leaks, have the shop put in a new one.

After the cap is tight or replaced, a code reader can clear the saved code. This small tool connects to a socket under the dashboard and displays the car's codes. You can buy one at an auto parts store. You can also simply keep driving; the light will turn off on its own eventually.

These figures are published averages. Your local shop may charge more or less.

RepairPal provided the shop prices, and Kelley Blue Book provided the purge valve price. Compared with a purge valve, a diagnosis costs far less, and it keeps you from buying a part your car doesn't need.

Yes, wherever the test is done by reading the car's computer. Cars built in 1996 or later all have this computer, known as OBD (short for on-board diagnostics). The tester plugs a cable into the socket under the dashboard and reads what the computer has stored. A saved code plus a lit check engine light means the car fails.

During 2026, cars are tested in 27 states and Washington, D.C. Some states test statewide; others test only in certain areas. Every state without testing is on the list of states that don't test. Electric cars never need the test.

As you drive, the car's computer checks its own pollution parts; these checks are called readiness monitors. If you clear the code or disconnect the battery, the car starts these checks over. Until you have driven enough, the test station sees them as "not ready". The station reviews the light and these checks during the test.

You usually need about 200 miles of driving to finish them. Your car can still pass with one or two checks unfinished, depending on its age. That limit is a national rule from the EPA (the government's clean-air agency), and most states use it, says New York's motor vehicle department. Find the model year on your registration card (it may differ from the year you bought the car):

A 2012 car, for example, may pass with one unfinished check. When two are unfinished, add more miles before test day. A leak that was never fixed makes the code and the light return.