P0442 Code in 2026: $0 to $1,500, Why a Small EVAP Leak Hides, and How Technicians Find It

P0442 is the hardest leak to find that still turns the light on: a sealed system, a hole smaller than a pinhead, and no drip or hiss.

GM put that in writing. Its small-leak bulletin, PIT4943D, opens by admitting that on some vehicles "a system leak cannot be verified through the system testing instructions," and that the difficulty "results in improper repairs and customers potentially returning for service with the same issue."

By the end you will know when your car runs its leak test, what a smoke machine can miss, which of five routes your P0442 belongs to, and what each costs, from a free look at a seal to a pipe that takes 12 hours to reach. Every 🟢 points to a document we read, listed at the end; every ⚪ is an estimate or owner report.

I built Pulscar, an AI tool that identifies car problems from a 30-second recording, after losing $6,000 to wrong diagnoses. The first lesson was a $380 bill for a noise three people called serious, which turned out to be a $5 heat shield.

How to use this guide

Routes are sorted by what has already been tried and what the test showed; with a small leak, failed fixes are the best clue.

One rule overrides everything: a P0442 is diagnosed with a leak test that can find a small leak, not with parts. A shop that cannot say how it tested has not found your leak.

First: is it really P0442? The EVAP codes compared

Codes stored beside P0442 change the route. The table matches our P0455 guide row for row.

Names differ, the test is the same. Mercedes-Benz calls P0442 a "Fine leak," Porsche a "Tank system fine leak," Audi and Volkswagen a "(Small Leak)."

Hole sizes are thresholds, not labels. 13 CCR 1968.2 requires detection of leaks that "cumulatively are greater than or equal to" a 0.040-inch orifice, and separately a 0.020-inch one, without assigning code numbers. Popular repair pages print inch ranges per code; no manufacturer document we read does.

Some P0442s are software. Volkswagen's 01-23-03 covers a 2022 Atlas calibration that stores P0442 in place of another code. Route 5.

Why a small leak is harder to find than a large one

A large leak is usually something open. A small one is a crack under a heat sleeve, a seal on the tank or a valve that almost closes, and four documented things hide it.

The test pressure is tiny. PIT4943D caps EVAP test pressure at 13 inches of water, "0.5 PSI," too little to push liquid out of a crack or make a sound ⚪.

Temperature moves the reading. GM says a large temperature difference between car, shop and tester "will seriously affect the accuracy of the tests." Mercedes-Benz found cars with M276 and M278 engines logging false fine leaks after winter fuel above 20 °C (68 °F), because the software was "too sensitive."

Some leaks exist only one way. GM's last resort is a vacuum test for a leak that "only exists under a vacuum condition." Smoke pushes; many cars' own tests pull.

The tester can be wrong. Audi found its leak detection pump "is causing a false leak detection" (Route 4); salt inside a Hyundai hybrid's leak sensor set leak codes too.

So "just change the cap" helps less often here: the cap is one joint among many, and the complaint file below shows how often owners bought one and kept the code.

When the car actually runs the leak test

Three quiet days after clearing P0442 prove little: the test may not have run. California's OBD rule sets the boundaries.

A full tank can skip the test. Section (e)(4.3.3): manufacturers "may disable or abort an evaporative system monitor when the fuel tank level is over 85 percent of nominal tank capacity or during a refueling event." 🟢

Cold starts matter. Section (e)(4.3.4) lets a manufacturer, with approval, run the EVAP test only on driving cycles it defines as cold starts. 🟢

Only some trips count. Toward the rule's required run rate, a trip counts only with a cold start, coolant between 40 and 95 °F and within 12 °F of the air, then 600 seconds or more in air of 40 to 95 °F. 🟢 A heatwave or a freezing week can pass with no counted trip.

Why the light waits. Under section (d)(2.2), the first failed test stores a pending code; the light comes on only if the next trip that runs the test fails too. 🟢

Manufacturers add their own conditions. Kia's manual test, PS469, requires the tank "at least half full before the test or it will not complete properly." Mazda's 01-002/18 says its workshop test ends early on a nearly full tank and must be rerun.

The practical window. A tank between half and three quarters, an overnight park, a mild morning and 10 minutes or more of driving give the test its best chance ⚪.

The 15-minute driveway protocol

1. Read all codes, including pending ones, and photograph them. A $20 to $40 reader that shows pending codes and monitors is enough.
2. Check for liquid fuel first. Under the rear, at the filler, in the cabin. A wet patch is not a vapor problem: the gas smell guide.
3. Remove the cap and look at the rubber seal, not the plastic. Cracks, a flattened ring, grit.
4. Look at the filler neck lip and the rubber around it. Cadillac found rubber rolled over the neck on some ATS sedans.
5. Check the readiness monitors. EVAP "not complete" after a recent clear means no verdict yet, not a cure.
6. Write down the history. Parts replaced, tests done, where the smoke was connected.
7. Look up the VIN on NHTSA and on the brand's owner portal. Emission recalls and campaigns sit there too.

Our diagnostic cost guide covers what the paid half should cost.

Eight ways a P0442 shows up

"The light came on and nothing else changed." → Route 1, then Route 2 if the cap is clean.

"I already bought a new cap and the code came back." → Route 2 or Route 3. Not a second cap.

"The shop smoke-tested it and found nothing." → Route 2.

"I smell fuel near a rear wheel, or after filling the tank to the top." → Route 3, after ruling out liquid fuel.

"It came back right after other work near the fuel tank." → Route 3, and ask the shop that did the work.

"I drive a work truck on dirt roads, or live on a salty coast." → Route 4.

"It is a newer Audi, Volkswagen or Mercedes-Benz and nothing leaks." → Routes 4 and 5.

"Inspection rejected the car for P0442." → Read the clearing section first, then pick a route.

What moves the price

The test. One proper test beats three quick ones; one Sonata owner reported seven.

Where the leak sits. A connector is minutes; GM allowed 12.1 hours for one Volt pipe.

Whether the tester is suspect. Bulletins replace a leak detection pump only after ruling out a real leak.

Your VIN. Recalls, campaigns and software updates are listed by build range.

The warranty clock. Usually 2 years or 24,000 miles for EVAP parts; Audi's pump bulletin runs to 48 months or 50,000 miles.

Where you drive. Dust and marine air appear as causes; GM bills its dust filter to the owner.

The price ladder, bottom up

Start at the last line and climb. With P0442, the gap between the top rungs and the free last line is usually one test done properly and one VIN lookup.

Your number by vehicle: the P0442 bulletins

Which route is yours? Five questions

1. Has nothing been replaced yet, and does the car drive normally? → Route 1. The cap seal and the filler.

2. Has a cap been replaced, or a smoke test found nothing, and the code came back? → Route 2. A valve that leaks while closed.

3. Is the car older, from a salt state, recently worked on near the tank, or does it smell of fuel when full? → Route 3. Cracks, chafe and joints.

4. Is it a dusty-duty truck, a coastal hybrid, or a newer Audi with a leak detection pump? → Route 4. The testing hardware.

5. Is your VIN on a recall, campaign, software update or open warranty? → Route 5. Do this lookup before any of the others.

The five routes, cheapest proof first

Route 1 · Nothing replaced yet — the cap seal and the filler

The tell. P0442 alone, a normal-driving car, no smell, nothing replaced.

What it actually is. The filler is opened by hand every week, so it earns the first look. Hyundai's bulletin 17-01-002, January 2017, is the cleanest example: on certain 2017 Santa Fe Sports "the fuel filler cap seal may not provide proper sealing," setting P0442 or P0456, and service campaign T1Q replaces the cap in 0.3 hours. Porsche's 150/22, September 2022, blames a cap defect for P044200 on 2021-2022 Carrera, Panamera, Macan and Cayenne models, and notes "There is no fuel leak at any time via the cap of the fuel tank" in that fault.

The filler, not only the cap. Cadillac's PIC6030 for 2013-2015 ATS sedans built before 9 August 2014 found the fuel filler pocket rubber "rolled over the fuel pipe neck," 0.2 hours to roll it back. GM's PIP6038, January 2025, names the cause on 2025 Trax and Envista models flatly: "Faulty fuel filler pipe."

Checking a cap without touching it. Mazda's 01-002/18 runs the EVAP test while the technician scans the cap with an ultrasonic leak detector, before anyone refits it. Nissan's NTB13-097J also starts at the cap; our P0455 guide covers it.

The cheap cause people walk past. The lip of the filler neck. A nick, grit or rust on the metal the seal presses against leaks exactly like a bad seal, and a new cap does nothing for it ⚪.

Fix it yourself — inspect, do not shop. Wipe the rubber ring and the filler lip, look for cracks, flat spots, a twisted ring or corrosion, and refit until it clicks; on a capless filler, check the flap for dirt. A damaged ring justifies one cap, ordered by the manufacturer's part number. The honest limit: if the seal looked fine, a new cap is a guess; after one cap, the next money goes to a test.

Where this does not apply. A code back after a new cap, a fuel smell or rough running after refueling: Routes 2 and 3.

At the shop — say this: "P0442, nothing replaced yet. Please check the cap and filler neck before disturbing the cap, run a leak test, and show me where it leaks before fitting parts."

Route 2 · New cap or a clean smoke test, and the code came back — a valve that leaks while closed

The tell. A new cap or a clean smoke test, and the code back within weeks. Sometimes P0441 or P0496 too, or a stumble after refueling.

What it actually is. During the leak test the purge valve, between canister and intake, and the vent valve, where the canister breathes, should both be shut. GM's 21-NA-124: "The leak can occur from a stuck open purge valve or stuck open canister vent valve." A valve that almost closes bleeds the test slowly, and smoke can escape into the intake where nobody sees it ⚪.

How GM tests it. PIT4943D, for 2016 and earlier GM cars and trucks, is the most detailed small-leak procedure we found. Command the system closed and watch tank pressure with the engine running for about two minutes. If vacuum appears, the purge solenoid is passing: pressurise its tank side with smoke, and "If smoke is allowed to pass through the purge solenoid, replace the purge solenoid." If not, stabilise the system for 5 minutes, add smoke, and check the cap, the vent solenoid filter and every quick connector.

Three more ways, same idea. Kia's PS469, "for hard to find/small leaks" on 2011 and newer Kias except the Sorento (XM) and Sedona (VQ), shuts the vent valve, unplugs the purge valve and watches tank pressure: if it "drops and continues to drop, the PCSV is likely to be leaking." Mazda's 01-002/18 holds vacuum on the purge valve at 60 kPa and again at only 10 kPa. Nissan's NTB13-097J adds a separate purge valve check on 2018 and newer models without a service port, and Audi's 2055592/1 checks the A3 e-tron purge valve hose for cracks.

What that looks like on paper. A 2015 Impala owner pasted dealer notes into a complaint (ODI 11222645): the technician "plugged the EVAP purge solenoid port and found EVAP pressure loss not present," and replaced the solenoid, twice in three months. A 2009 Corvette owner (ODI 11564943) replaced the cap first; a smoke test then "found that the evap vent solenoid was leaking."

The cheap cause people walk past. The test itself. PIT4943D warns that aftermarket testers "may not have the same pressure regulation," and a quick smoke test on a car straight off the road is weak evidence ⚪.

Where this does not apply. Do not assume the valve. GM's PIP5862 for 2021-2022 Encore and Trax says returned purge solenoids and purge pumps "have been tested with no problems found," and Ford reported the same, as the P0455 guide describes. A fuel smell or visible cracking points to Route 3.

At the shop — say this: "P0442 is back after a new cap and a clean smoke test. Please test the purge and vent valves for leakage while closed, and tell me which result condemned a part before replacing it."

Can you hear a P0442? Usually not. A crack in a vapor hose at half a PSI makes no sound you could record. What you can hear is the one P0442 cause that changes how the engine runs: a purge valve stuck open. A 2020 Impala owner (ODI 11744373) described stumbling and failure to start immediately after refueling, with rough idling, and P0496 or P0442 stored. A 2019 Trax owner (ODI 11710113) said a new purge valve under GM special coverage "fixed post-refuel roughness." That unsteady idle in the minutes after a fill-up is a sound. Record 30 seconds of idle straight after your next fill-up and Pulscar's AI compares it with catalogued failure patterns, then returns the likely cause, whether the car is safe to drive, and a fair 2026 price range. Free, no card, no subscription; the report arrives by email in about ten minutes.

Route 3 · Older car, salt, recent work near the tank, or a smell when full — cracks, chafe and joints

The tell. An older or salt-belt car, a fuel smell after parking or a full fill, or a code soon after work near the tank.

What it actually is. Lines rub and crack, clips stay unseated, tank seals age, and none of it drips. The Volt is the documented extreme: GM's service update 17197, June 2017, for about 30,220 2016-2017 cars, found an EVAP pipe rubbing an air conditioning hose, where "such contact may wear a hole into the pipe." Emission recall N192273600, March 2020, widened it to about 72,921 2016-2019 Volts: a bumper and tie straps in 0.8 hours, and for the 1% of VINs that need a new pipe, 12.1 hours more.

Rubbing and loose joints elsewhere. Buick's PIC5861, 2010-2012 LaCrosse V6: check the pipe "for contact with the throttle body." Volkswagen's tip TT 26-16-02, 2015-2016 Passat: secure all canister connections "regardless of test plan results." A 2019 Equinox owner at 957 miles (ODI 11234911) said the dealer "found purge tube not seated fully," and later a failed canister O-ring.

Seals on top of the tank. Kia's PITSTOP PS567, November 2020, for 2017-2018 Cadenza and certain 2017 Optima Hybrids: when lines, cap and circuits test good, inspect the fuel pump seal and replace it if "torn or split." A 2009 Mazdaspeed3 owner (ODI 11439442) said a smoke test traced the leak to the fuel pump lock ring.

After someone else's repair. Two Land Rover LR4 owners (ODI 11534663 and 11746689) reported P0442 soon after fuel tank flange work under recall 21V-635, which covers 111,746 2010-2013 Range Rover Sport and 2010-2016 LR4 vehicles. That recall is about liquid fuel, not EVAP; the lesson is that disturbed seals near the tank are prime suspects.

The cheap cause people walk past. Soapy water. Volvo's Technical Journal TJ 33198 says that if smoke is not clearly visible, "spray all visible connections and/or openings with soapy water to locate the leak," then rerun the quick test to confirm.

Fix it yourself — trace the lines you can reach. Engine cold, level ground, a good torch. Follow the thin vapor lines from the intake back along the firewall, tug each quick connector gently, and look for shiny rub marks where a line touches metal. Under the rear, check the canister hoses for cracks or a line hanging free; a 2009 Forester owner (ODI 11535637) found "one of the evap hoses was just hanging next to the fuel tank." The honest limit: never work under a car on a jack alone or open fuel lines; tank-top seals are shop work.

Where this does not apply. Visible liquid fuel is no longer a small EVAP leak; have it inspected before driving far. A stumble after refueling is Route 2.

At the shop — say this: "P0442 on an older car. Please smoke test it at shop temperature, use soapy water if the smoke is faint, and send me a photo before lowering the tank."

Which P0442 repairs does the carmaker pay for, and which land on you? The answer sits in paperwork tied to your VIN. A 2016-2019 Chevrolet Volt listed under emission recall N192273600 gets its purge pipe protected, and replaced if worn, at no charge, and GM set a March 31, 2021 deadline for reimbursing owners who had already paid. Certain 2017 Santa Fe Sports get a new cap under Hyundai's campaign T1Q, and 2011-2015 Sonata Hybrids get an air filter and, with a leak code stored, a new leak sensor under campaign T6H. Audi's pump bulletin is written for claims up to 48 months or 50,000 miles. Everything else usually falls under the federal emissions warranty of 2 years or 24,000 miles, and GM's dust filter for pickups is customer-paid by design. Pulscar checks whether an unsteady post-refuel idle sounds like a valve fault before anyone quotes you.

Route 4 · Dust, salt, or the tester itself — when the part running the test is the problem

The tell. A truck on gravel roads, a hybrid near the ocean, or a recent Audi where nobody can find a leak.

Dust makes a blockage look like a leak. On GM pickups driven "in extremely dusty environments" (2019-2025 Silverado and Sierra 1500, 2020-2025 HD), bulletin 23-NA-073 of March 2025 says dust "can plug the canister and canister vent solenoid" and set P0442, P0446, P0455 or P0449. The fix is an inline filter, "a customer pay alteration," checked periodically afterwards. Our large-leak guide covers the dust story; for P0442 the point is that a small-leak code on a dusty truck can be a blocked vent, not a hole.

Salt in the sensor. Hyundai's campaign 21-01-035H, June 2021, for 2011-2015 Sonata Hybrids: the conditions "primarily occur in the California coastal areas that are subject to marine layer cloud cover," where salt forms inside the natural vacuum leak detection sensor and triggers P0442, P0455 or P0456. Campaign T6H fits an updated air filter in 0.5 hours, plus a new sensor, 0.7 hours in total, when a leak code is stored; bulletin 21-FL-002H describes the same salt.

A pump that reports leaks that are not there. Audi's 2065287/4, September 2022, covers 2017-2021 A3, Q7 and TT and 2019-2021 A6, A7, A8, Q3 and Q8, among others: "The EVAP leak detection pump (GX36) internal defect is causing a false leak detection." The order matters: first "Confirm that there is no leak present in the system caused by other components," then replace the pump. An earlier bulletin, 2060032/1, covered 2019 and early 2020 Q5s.

The cheap cause people walk past. The fresh-air inlet filter, where the canister breathes, often reachable without lifting the car ⚪.

Where this does not apply. A garaged car with no bulletin is unlikely to be here: Routes 2 and 3. On 2021-2022 Encore and Trax, PIP5862 replaces the canister only after the leak test finds nothing.

At the shop — say this: "P0442 on a car used in dust or near the coast. Before replacing a canister or leak detection pump, please rule out a real leak, check the vent filter, and look for a bulletin on this VIN."

What does a P0442 actually cost to fix in 2026? It depends on where the leak hides. At the bottom: a cap seal inspection for nothing, a replacement cap at $10 to $25 as a part if the seal is damaged, and a code reader for $0 to $40. In the middle: a smoke test at $50 to $150, a diagnostic fee of $80 to $150 at an independent shop or $120 to $200 at a dealer, an unseated connector or split hose at $15 to $150, a purge valve at $150 to $300 installed and a vent valve at $150 to $350. Higher: a leak detection pump at $400 to $900 on most cars, a filler neck at $200 to $500, a canister at $200 to $650, and seals on top of the tank or a buried pipe at $400 to $1,500. Recalls and campaigns take some of those to zero. Pulscar prices your recording against these ranges before a shop prices it for you.

Route 5 · A document covers your VIN — software, campaigns and warranty

The tell. A recent model with no findable leak, a letter from the manufacturer, or a dealer that mentions an update.

When the code is the software. Volkswagen's 01-23-03, March 2023, for 2022 Atlas and Atlas Cross Sport 2.0T: "Current engine software may incorrectly store a P0442 DTC instead of a P2450 DTC," and "DO NOT diagnose or replace components due to the above faults before performing the update." Mercedes-Benz's LI47.40-P-053871, May 2014, on the false fine leaks described above, rules: "If there is no identifiable leak in the fuel system, no components may be replaced." New software was the fix.

When the maker wants to see it first. Audi's repair authorization 2069166/1, January 2023, for 2022-2023 Q5 and SQ5 2.0L with P044200: "Various parts have been replaced under warranty for the condition noted above, but no issues were identified with these parts." Dealers must call Audi before replacing parts; ask whether yours did.

The recall with a deadline. GM's Volt emission recall N192273600 warns that a car "may fail a state or local emission inspection if this recall is not accomplished." One 2018 Volt owner told NHTSA (ODI 11716611) the dealer quoted $5,093, then $2,384, for the same code at the same spot after the recall bumper was fitted.

The cheap cause people walk past. The warranty clock. The federal statute, 42 U.S.C. 7541(i), gives most emission parts 2 years or 24,000 miles; the longer 8-year, 80,000-mile term is limited to the catalytic converter, the emissions computer and the onboard diagnostic device. Our P0455 guide covers California's longer terms and Kia's canister extension.

Where this does not apply. A bulletin is not a recall: your warranty decides who pays. A VIN outside the range can have the same fault; it just is not free.

At the shop — say this: "Please check this VIN for recalls, emission campaigns and software updates for P0442, and tell me the in-service date before quoting any EVAP part."

What a small leak sounds like, and what it does not

Silence is normal. A vapor leak at a fraction of a PSI makes no sound.

The stumble after refueling is not silent. A purge valve stuck open floods the engine with vapor when the tank is fresh; that uneven idle is the one P0442-related symptom you can record.

A light ticking from a purge valve is often normal. Many purge valves click rapidly at idle while purging, and that sound alone is not a fault ⚪.

A pop from the back. The Equinox owner (ODI 11234911) also heard a "loud pop coming from rear of car." One report proves nothing ⚪.

Fuel smell at a full tank. A 2013 Corvette owner (ODI 11222826) noticed a strong odour after filling to the top and "no gas odor when filling tank only one-half full." That points at joints high on the tank or the filler ⚪.

Our study of noises without a warning light shows how often trouble is heard first.

What the 30 federal complaints naming P0442 found

Our sample: 777,040 unique complaints added to NHTSA's files from 1 January 2015 to 8 September 2026, searched for the exact code. 30 name P0442, against 47 for P0455 and 133 for P0456. No model has more than 3, so we rank nothing; Chevrolet has 12, and the 13 stated mileages have a median of 56,000.

The cap. Seven owners replaced the gas cap and still had the code, some more than once. One, a 2002 Camry owner keeping a service log (ODI 10735783), recorded a faulty cap as the fix. Complaints come from people whose problem was not solved, so this is not a success rate.

Where leaks were found. A purge valve or solenoid in 3 reports, one found by plugging its port during a pressure test; a vent valve or solenoid in 2; an unseated or loose hose or tube in 2; a filler neck or filler tube in 2; seals or fittings at the top of the tank in 3, including a fuel pump lock ring; and new codes after fuel tank recall work in 2. Some reports name more than one finding. Four owners never got an answer, including a 2009 Sonata owner (ODI 11170436) who wrote "we also did 7 smoke tests and still can not find the issue."

The warning inside the numbers. Four of the 30 describe liquid gasoline, not just a code: at the filler, in the rear seat area, on the ground or pouring from the tank. Seven mention a fuel smell. P0442 does not rule out a fuel leak.

What we checked. Recall 21V-635, cited in one complaint, is a Land Rover fuel tank flange recall, not an EVAP one.

P0442 before an inspection: why clearing it backfires

A lit light fails. The federal OBD inspection rule, 40 CFR 85.2222, says a car with the light commanded on "shall fail the OBD inspection."

A cleared code is not a pass. Clearing resets the readiness monitors, and the same rule turns away 2001 and newer vehicles with more than one unset.

The code is more stubborn than it looks. Under 13 CCR 1968.2, a confirmed code is also stored as a permanent fault code that a scan tool cannot erase; it clears only after the monitor runs and passes. Repair, drive a week, confirm the monitor, then book the test. The inspection cost guide covers re-test fees.

At the shop, checkpoint by checkpoint

Checkpoint 1 — the paperwork. "Does this VIN have any recall, campaign, software update or open technical case for P0442?"

Checkpoint 2 — the full picture. "Which EVAP codes are stored, pending or permanent, and what is the monitor status?"

Checkpoint 3 — the method. "Where was the smoke connected, was the cap left undisturbed, was the car at shop temperature, and was it tested under vacuum as well as pressure?"

Checkpoint 4 — the valves. "Were the purge and vent valves tested for leakage while closed, and what did they show?"

Checkpoint 5 — evidence and a spending limit. "Can I see a photo of the leak or the failed test reading, and will you call before anything over this amount?" The overcharging guide explains how estimates grow.

Three ways a P0442 diagnosis goes wrong

Trap 1: the second and third cap. The situation: P0442, a new cap, the light back in a week. What the shop says: "Aftermarket caps don't seal. Buy the dealer one." What is really happening: GM's small-leak bulletin lists the cap as one of several checkpoints, and seven complaint-file owners kept the code after a new cap. Price versus bill: a $50 to $150 test, against $10 to $25 caps and weeks lost. Your protective question: "Did a test show the cap leaking, or is this a guess?"

Trap 2: the clean smoke test that ends the search. The situation: a quick smoke test on a car straight off the road finds nothing. What the shop says: "No leak. We cleared it. Come back if it returns." What is really happening: GM warns that temperature distorts small-leak tests and some leaks exist only under vacuum. Price versus bill: one proper test, against the same quick test at the next shop. Your protective question: "Was it tested under vacuum too, and where was the smoke connected?"

Trap 3: the leak detection pump or canister replaced first. The situation: a newer car with P0442 and no visible leak. What the shop says: "That pump always fails on these. New canister while we're in there." What is really happening: Audi replaces its pump only after ruling out other leaks, and GM saves the Encore and Trax canister for last. Price versus bill: a test and a VIN check, against a $400 to $900 pump plus a $200 to $650 canister that may not be the fault. Your protective question: "What test ruled out every other leak first?"

Three quotes, decoded

These are composite scenarios, not individual customers: numbers and outcomes drawn from the documents and complaints above, combined so the arithmetic is visible.

Scenario 1 — the Impala that needed a plug, not a canister. A 2015 Impala, P0442, a new cap already fitted. First quote: $520 for a canister and cap. A second shop follows GM's method, plugs the purge solenoid port, and the pressure loss stops: a purge valve at $220 installed, plus a $120 test. Lesson: the test that isolates one part is the cheapest part of the job.

Scenario 2 — the Volt that was on a list. A 2018 Volt, P0442 again after earlier work. The quote is over $2,000 for a pipe replacement. The VIN shows the emission recall, and the dealer handles it under the recall. Lesson: when a document names your code and your model, the VIN check comes before the estimate.

Scenario 3 — the Atlas with nothing to fix. A 2022 Atlas 2.0T, P0442, no leak found by smoke. A quote of $450 for a leak detection pump. The dealer checks bulletin 01-23-03, updates the software, and the code does not return after a week. Lesson: on a new car, ask about software before hardware.

Your situation right now: four playbooks

"The light just came on." Photograph the codes, check the cap seal and filler lip, and give the car a week of normal driving before paying anyone.

"New cap, and it is back." Stop buying caps. Ask for a leak test that includes the purge and vent valves.

"A shop found nothing." Ask where the smoke went in, whether vacuum was tested, and whether the car had cooled to shop temperature.

"It failed inspection." Repair, drive a week, confirm the EVAP monitor with a reader, then re-test. The check engine light guide covers anything else stored.

After the fix: verify, then prevent

A finished monitor is the proof. Give it a week of cold starts on a part-full tank; your reader should then report EVAP complete with nothing pending.

Stop at the first click. Topping off after the pump shuts off is widely blamed for pushing fuel into places built for vapor ⚪; the Corvette owner above smelled fuel only on a full tank.

Keep the breathing side clean. Dusty-duty trucks need the GM vent filter inspected on schedule. A 30-second clip of your healthy post-refuel idle makes a useful baseline; the recording guide shows how.

Your action plan: 10 minutes, today, this week

Next 10 minutes — free:

1. Save all codes and the monitor status. Do not clear anything.
2. Check for liquid fuel and a fuel smell in the cabin.
3. Inspect the cap seal and the filler lip.

Today:

4. Run the VIN through NHTSA and the brand's owner site for recalls, campaigns and updates.
5. After the next fill-up, record the idle and send it for the free check.

This week:

6. If the code stays, get a leak test that covers both valves, pressure and vacuum.
7. Approve only the part a test proved bad, and watch the EVAP monitor finish.

Sources and documents

Primary documents, opened and read in September 2026; years, populations and quotes come from the documents.

1. GM PIT4943D, December 2015. PDF
2. GM 21-NA-124, December 2022. PDF
3. Cadillac PIC6030, September 2014. PDF
4. Buick PIC5861, July 2013. PDF
5. GM PIP5862, 28 July 2022. PDF
6. GM PIP6038, 22 January 2025. PDF
7. GM PIP5461, January 2017; service update 17197, June 2017; emission recall N192273600, revision 01, March 2020. PIP5461 · 17197 · N192273600
8. GM 23-NA-073, March 2025. PDF
9. Nissan NTB13-097J, 7 February 2022. PDF
10. Kia PITSTOP PS469, January 2017. PDF
11. Kia PITSTOP PS567, revision 2, 20 November 2020. PDF
12. Mazda 01-002/18, 30 January 2018. PDF
13. Hyundai 17-01-002 (campaign T1Q), January 2017. PDF
14. Hyundai 21-01-035H (campaign T6H) and 21-FL-002H, both June 2021. 21-01-035H · 21-FL-002H
15. Audi 2065287/4, 14 September 2022; 2060032/1, 15 July 2020; 2069166/1, 17 January 2023; 2055592/1, 15 July 2019. 2065287/4 · 2060032/1 · 2069166/1 · 2055592/1
16. Volkswagen 01-23-03 (2069659/1), 7 March 2023, and tech tip TT 26-16-02, 18 March 2016. 01-23-03 · TT 26-16-02
17. Mercedes-Benz LI47.40-P-053871, version 8, May 2014. PDF
18. Porsche Technical Information 150/22, 15 September 2022. PDF
19. Volvo Technical Journal TJ 33198, November 2017. PDF
20. NHTSA recall 21V-635 (Land Rover N623). Recall record
21. Law and rules 13 CCR 1968.2 · 40 CFR 85.2222 · 42 U.S.C. 7541
22. Our complaint sample Field definitions · ODI 10735783 · ODI 11170436 · ODI 11222645 · ODI 11222826 · ODI 11234911 · ODI 11439442 · ODI 11534663 · ODI 11535637 · ODI 11564943 · ODI 11710113 · ODI 11716611 · ODI 11744373 · ODI 11746689
23. Leak detection pump price range PartCatalog cost guide

Not found. NHTSA's index lists GM 15-NA-019, Jaguar JTB00436 and Land Rover SSM71658 and SSM72183 for P0442, but their PDFs were not on NHTSA's server, so we make no claim from them. We found no Toyota bulletin naming P0442.

Related: P0455 large leak, gas smell, most expensive codes, P0171, P0420, diagnostic costs, our story.

Methodology. Documents were downloaded from NHTSA's server and read as text; the regulation text comes from Cornell's Legal Information Institute. Complaint counts come from NHTSA's complaint flat files, de-duplicated by report number; they are owner reports, not audited repairs, and quoted phrases were checked against NHTSA's complaint records. Prices were checked in September 2026 against published estimator summaries and kept consistent with our P0455 guide; all are estimates marked ⚪. Coverage depends on your VIN.

Prices verified: September 2026 · Technical documents verified: September 2026 · Reviewed quarterly

Found a hidden P0442 leak, or paid for parts that did not fix it? Write to [email protected] with the model year, engine, mileage and the test result that finally located it; we use owner reports to tighten these ranges.