EVAP Leak Questions, Answered From Sources

Your car stores gasoline vapor in a charcoal canister and later burns it in the engine. The computer must check that whole system for vapor leaks to the air. An EVAP leak means vapor can escape somewhere, like a loose cap, a cracked hose, or a bad valve.

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Several carmaker bulletins about EVAP leak codes say drivability is not affected. CARB says most makers advise service as soon as it is convenient, and a blinking check engine light needs fast service. A few recalls are different. A stuck purge valve could stall some Ford Focus engines, so check for open recalls on your car.

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None of our sources give a set number of miles or days. Bulletins say a small leak code does not change how the car drives, and CARB says to get service when it is convenient. If the light stays on, the car can fail smog or an emissions test in many states.

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Most EVAP codes are emissions problems, and bulletins say the car drives the same. Some related faults are safety recalls. A leaking purge valve cracked fuel tanks on some 2010 to 2011 Fusion and Milan cars, causing fuel leaks or fuel odor. Leaking fuel near a spark can start a fire. If you smell raw fuel or see a drip, get it checked right away.

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In California, yes. A car fails the OBD part of smog check if the check engine light is commanded on or any trouble code is stored. Many other states fail a car when the check engine light is on with a stored code. Check your state in our emissions table.

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In California, a 2000 or newer gas car may pass with only the EVAP monitor not ready, and 1996 to 1999 cars may have one monitor not ready. BAR adopted a rule in 2025 that all monitors must be set, but says the old allowances stay in use while it studies the data. Other states allow one or two not ready monitors by model year.

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Yes. Ford lists a cap that was not put on right as a cause of P0455, and has a separate P0457 code for cap off. Acura, Mazda and Honda bulletins also tie EVAP codes to caps that do not seal. Fueleconomy.gov names a loose gas cap as one possible reason for the light.

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It depends on the car. CARB lets the light go off once the system checks that the cap is tight. Otherwise the light goes off after three drive cycles in a row where the EVAP test runs and passes. Ford says the code and light clear as soon as normal purge vacuum passes a stored level. The EVAP test only runs under certain conditions, so it can take days.

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Some cars have a separate light for a loose or missing cap. On Fords it can come on with code P0457 after a fill up. CARB lets makers use this light in place of the check engine light for a cap problem.

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The rules use test holes. A small leak is about the size of a 0.040 inch hole (often P0442). A very small leak is about 0.020 inch (P0456). A large or gross leak (P0455) means the system could not even hold its test vacuum, which Ford says can come from a loose cap or a disconnected line.

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Common causes in carmaker documents include a loose or bad gas cap, filler neck parts, split or kinked vapor hoses, a purge valve stuck open or closed, a vent valve stuck open or blocked by dirt, water or spider nests, and a bad tank pressure sensor or leak check pump. Overfilling the tank can also soak parts with fuel.

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None of our sources rank leak spots by how often they happen. Carmaker bulletins point often at the gas cap and filler neck first, then hoses, the purge valve and the vent valve.

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It can. Ford said a leaking purge valve could crack the tank and cause a fuel leak or fuel odor on some 2010 to 2011 Fusion and Milan cars. VW said fuel that collects in the EVAP system can cause a fuel odor on some 2015 to 2020 models. A strong raw fuel smell should be checked soon.

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We found no primary source that puts a number on mileage lost to an EVAP leak. Fueleconomy.gov says the check engine light can mean something as minor as a loose gas cap, or a bigger problem that could lower fuel economy.

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It depends on the part. RepairPal lists about $138 to $150 for a gas cap, $210 to $251 for a purge valve, $356 to $457 for a tank pressure sensor and $558 to $643 for a canister, with parts and labor. CarMD's 2026 report lists an average of $172 for a purge valve. See our cost table for each source and date.

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Supercanic in San Jacinto, California billed an EVAP smoke test as 1.0 hour of labor at $150 on a 2005 Mercedes E55 in September 2026. RepairPal lists $61 to $90 labor for general emission system diagnosis.

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Shops run the carmaker's EVAP test with a scan tool, then use a smoke machine to find where the leak is. Mazda's bulletin uses a smoke tester. FCA says to leave the original gas cap on during the test, because a test adapter can hide a cap leak.

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Monitors reset when codes are cleared or the battery is disconnected. The EVAP test also only runs under set conditions. Makers may skip it when the tank is over 85 percent full, and Ford needs about 15 to 85 percent fuel, a cold soak and steady driving. Toyota's test runs after the car sits about five hours.

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Drive the car through a drive cycle, often two, with a cool down between them. Check your owner's manual for the maker's cycle. Keep the fuel level between about 15 and 85 percent, since makers may skip the test above 85 percent and Ford's test needs at least 15 percent. On many Toyotas, letting the car sit about five hours runs the leak check.

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Fix the cause first. The light then goes off on its own after three drive cycles in a row with a passing test, and the stored code is erased after 40 warm up cycles. Clearing codes with a scan tool resets the monitors to not ready, which can fail an inspection until you drive enough to set them.

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P0455 means the computer found a large or gross EVAP leak. Ford lists a cap not put on right, a large hole, loose or kinked vapor lines, a vent valve stuck open, or a purge valve stuck closed as causes.

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P0456 means a very small leak, about the size of a 0.020 inch hole. Causes in bulletins include a cap that does not seal, filler neck parts, split hoses and leak check sensor problems.

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P0442 means a small EVAP leak. On Ford's test it is a 0.040 inch leak. GM, Mazda and Audi bulletins tie it to a stuck purge valve, a loose cap, vent valve corrosion, or leaks in the system.

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The purge valve opens to let the running engine pull stored fuel vapor out of the charcoal canister and burn it. During the leak test, the computer also uses it to pull vacuum on the sealed system.

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Signs in carmaker documents include EVAP codes such as P0455, P0442, P0496 or Ford's P1450. Recalls also list engine stalls, a wrong fuel gauge from a deformed tank, and in some cases a cracked tank with fuel odor.

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No. GM says to stop after the pump nozzle clicks off. More than three extra clicks is too much and can push liquid fuel into the EVAP system and set a code.

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A blocked vent path is one cause. GM found dirt or water at the canister vent valve could make some SUVs hard to fill. FCA says to check for a kinked clean air hose, a plugged EVAP air filter or a pinched vapor hose before replacing the canister.

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Labor times in our sources run from 0.3 hour to replace an Acura gas cap and 0.8 hour for a Honda canister job, to the 1.0 hour Supercanic billed for a smoke test.

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