P0442 and P0455 Fixes Cost $15 to $650. Start at the Gas Cap

Two drivers pull the same P0442. One finds a cracked seal, buys a $15 to $40 gas cap and is done. The other has a good cap, so a shop runs a smoke test for $100 to $180 and finds a stuck valve or a split hose.

I'm Anthony, lead technician at Supercanic, the shop in San Jacinto and Hemet that runs MechanicRank, where we list 48,054 shops and mechanics. Start with the cap, because it's free to check. Just don't let anyone sell you a canister before they've shown you the leak.

What P0442 and P0455 Mean

Gas gives off fumes. Your car stores them in a charcoal canister, then a purge valve lets the engine pull them in and burn them. A vent valve seals the system so the computer can test it. Our EVAP repair guide covers each part.

California's OBD II rule tells the computer to flag leaks equal to a 0.040 inch hole, and then a 0.020 inch hole. The federal rule names P0456 as an example code for that 0.020 inch leak. P0442 is the small leak code above it.

The names can fool you. Kelley Blue Book calls P0455 a gross leak, then warns it may look really small. And one of our own scan tools labels P0442 a medium leak, not a small one.

From GM bulletin 21-NA-124, Kelley Blue Book and our EVAP repair guide. Carmakers set their own test limits, so read your code next to your car's service information.

What Each EVAP Fix Costs

These come from our own repair cost guides. Each repair adds the part price to the book labor time at $95 to $140 an hour, for a typical car at an independent shop.

• New gas cap, you fit it$15 to $40
• Purge valve, parts and labor$95 to $405
• Smoke test alone$100 to $180
• Smoke test plus a common fix$115 to $650

MechanicRank repair cost guides as of October 2026, national labor rate of $95 to $140 an hour, quality aftermarket parts, before sales tax. Not a quote for your car.

In California, at the $120 to $175 an hour our guides use, the purge valve runs $110 to $460 and the full EVAP repair runs $140 to $740.

That top number has limits. Our guide warns that a rusted filler neck or a tank seal can cost more, because the labor to reach them is the bill. Hybrids and many European cars also cost more, since they can use sealed tanks or leak detection pumps.

RepairPal's code page has no prices at all. You get a list of causes and no idea which one to budget for, so use this chart instead.

Check the Gas Cap First

RepairPal and KBB both put the cap first. Our EVAP guide does too, and a Nissan bulletin says a cap left loose for several trips will store these codes and turn on the light.

• Look at the seal. Take the cap off. The rubber should be soft, round and free of cracks.
• Tighten it until it clicks. Do this with the engine off, since KBB says fueling with it running can set P0455.
• Read the dash. Many cars have a loose cap message. Nissan says to stop safely and reseat the cap if you see it.
• Buy the right cap. Our guide warns that cheap caps often don't seal well. KBB suggests trying a known good cap when nothing looks wrong.
• Give it time. Drive normally for several days. The computer has to run its test and pass, and that can take a week or more.

California's rule even allows for this. Where the computer can tell the leak came from a loose cap, it may turn the light off once the cap is secure. That depends on the car, so don't count on it.

One job of ours shows why the cap stays on the list. A 2013 GMC Yukon had a smoke test on our ticket in August 2026. It came back in October with the same kind of light, a recurring code. Our tech billed a $125 diagnostic, and the note on the job says the gas cap needed replacing with a factory one. I can't tell you the first test was wrong. I can tell you a good cap check is worth doing twice.

Match the Clue to the Part

A code alone won't tell you which part failed. What the car does around the code often will.

Clues from our EVAP and purge valve guides and GM bulletin 09-06-04-028D. National labor rates. A strong smell of raw fuel can be a liquid leak, so get that looked at soon.

What a Smoke Test Should Include

A machine fills the sealed system with harmless smoke, and the smoke comes out where the leak is. Our guide puts the test at $100 to $180. On our own tickets, one estimate listed an EVAP smoke test at $125 on a 2015 Nissan Altima. A smoke test on a 2005 Mercedes E55 billed at $150, though that one hunted an intake leak.

The test only proves something if it's done right. GM's bulletin 21-NA-124, which covers its gas engines from 2000 to 2021, says some leaks show up only under pressure and some only under vacuum. It recommends checking both ways. It also gives a set order, and I like it because the cheap checks come first.

• Lines first. Confirm every EVAP line is installed and fully seated.
• Damage next. Look for cracks and wear, then confirm with smoke.
• Vent valve. Check whether it's stuck open.
• Purge valve last. Check it once the lines and vent valve pass. A scan tool that cycles both valves can show one sticking.

Nissan's bulletin NTB13-097J goes a step further. It has the tech close the vent valve with the scan tool, pressurize the system and watch a gauge for 10 minutes. It also says a test drive for these codes will only waste time. If a part replaced under warranty turns out to work, Nissan charges the dealer back for it. Guessing costs even the dealer money.

So ask for proof. A shop that found the leak can show you a photo or video of the smoke. Ask whether the test fee counts toward the repair, because some shops credit part of it. Mobile mechanics can do many of these jobs too, so ask whether they carry a smoke machine. Without one, they're guessing.

Four Bulletins Worth Reading

Carmakers file these with NHTSA, and few owners ever see them. These are examples, not a full list. A bulletin covers only the cars it names, so call a dealer with your VIN to see if one fits.

Read from the carmaker bulletins linked in each row, on NHTSA's server. Bulletins are written for trained technicians.

Samarins reports a Toyota bulletin too, EG051-06, on corrosion at the cap sealing surface of the filler pipe on some 2003 to 2005 Corollas and Matrixes. That's a good reminder. A new cap can't seal against a rusted neck.

Can You Drive With It

Usually yes. Our guide says an EVAP leak won't hurt the engine or leave you stranded. RepairPal rates P0442 as moderate and says to diagnose it within a reasonable time. KBB says P0455 doesn't affect performance.

I'd still fix it, for three reasons. The light stays on, so you won't see the next fault when it shows up. Fumes are escaping, and a fuel smell means you should go sooner. And if your area tests emissions, you'll have to deal with it anyway.

California's Bureau of Automotive Repair says a car won't pass Smog Check with the light on. BAR's reference guide also says inspections are OBD focused for most 2000 and newer cars, and lists a fuel cap test and a low pressure evaporative test among its functional tests where they apply. See our smog check guide for what the test itself costs.

Check Your Warranty and California Help

EVAP parts don't get the long federal term that catalytic converters get. CARB's warranty fact sheet lists 8 years or 80,000 miles for converters, the emissions control unit and the OBD computer. The federal basic term is 2 years or 24,000 miles, for any part that causes an emissions failure.

California cars get more. The same sheet lists 3 years or 50,000 miles on all emissions related parts, and 7 years or 70,000 miles on high cost parts listed in your owner's manual. Read that list before you pay for a part.

If your car failed its biennial Smog Check, California's Consumer Assistance Program may help with repairs. It pays up to $1,450 on a 1996 or newer car, if your household income is at or below 225% of the federal poverty level. Wait for your eligibility letter before any repair starts.

What Our Own Jobs Show

We don't have enough EVAP tickets to call it a study, so read these as examples. They're Supercanic tickets. The diagnostic line comes from our public study of 953 paid jobs, August 2025 to October 2026, on our mobile mechanic prices page.

Supercanic job tickets and paid job study, before sales tax. Each row is one job unless it says otherwise. Your car will differ.

Both purge jobs landed inside our $95 to $405 range, in the lower half. Shops that post a diagnostic price on their own websites post a median of $100, with the middle half between $80 and $150, per our check engine light diagnostic guide. An EVAP hunt can take longer than a basic scan, so ask what the fee includes.

Old Advice That Stuck

Clear the code and see. Clearing it takes the light off and proves nothing. The computer still has to run its leak test and pass. BAR suggests a week or two of driving after a battery change so monitors can reset, and I'd plan the same before a retest.

P0455 means a big hole. GM's bulletin says it can come from a stuck closed purge valve. So a shop that hunts only for a gaping hole can miss it.

Replace the canister. Our guide lists the canister near the end of the usual suspects. Ask to see smoke coming from it first.

Keep topping off the tank. Stop when the pump clicks off. Our guide warns that topping off pushes liquid fuel into the canister, and that can ruin the canister and the valves around it.

Find a Shop for the Job

MechanicRank lists 48,054 repair shops and mechanics in 6,649 cities. Every listing shows the shop's phone, reviews and hours, and the phone rings the shop direct. Search your ZIP code and ask for a smoke test that checks both pressure and vacuum before anyone quotes a part.

At Supercanic, our own shop, labor is $150 an hour, with a 90 day or 5,000 mile labor warranty.

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