P0442 EVAP system small leak detected

EVAP small leak

Monitor

EVAP faults let fuel vapour escape but rarely change how the car drives, and the main risk is a failed emissions test, so it is safe to drive while you arrange a fix.

It gets more serious if:

  • Inspect soon: You keep smelling raw fuel around the car, not just right after filling up
  • Stop: You see liquid fuel dripping or pooling under the car, or near the filler, tank or canister

Source: how we rate severity

P0442 in short

P0442 means the computer found a small leak in the fuel vapour (EVAP) system. The usual first suspect is the fuel cap or its seal, then cracked hoses, the vent valve or the canister. It is generally safe to drive, but get a strong or lasting fuel smell checked soon.

The EVAP system traps fuel vapour from the tank in a charcoal canister and feeds it to the engine to burn. Every so often the computer seals the system and checks it holds vacuum or pressure.

Regulations require it to catch leaks about 0.040 inch across, and P0442 is the small-leak code. P0455 is the larger leak and P0456 the smaller one.

Small leaks often come from the cap seal, ageing hoses or a valve that does not seal fully. Several makers have bulletins for specific P0442 causes, from canister welds to dust-fouled vent valves.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Loose, damaged or non-factory fuel cap

    Common general cause
    Why it ranks here
    Cap and cap-seal problems are the most common driver-side cause, and EPA and makers say to check them first.
    What would change this
    Falls if the cap is factory, clicks and has a sound seal.
    How to test the fuel (gas) cap

  2. Canister vent valve that does not seal, or is fouled by dust

    Possible — needs testing
    Why it ranks here
    GM bulletins name the vent solenoid for P0442 twice: one leaks under vacuum when cold, and on trucks dust can foul it.
    What would change this
    Rises if P0446 or P0449 is also stored, or the valve leaks under a vacuum check.
    How to test the evap canister vent valve

  3. Split, cracked or disconnected EVAP hose

    Common general cause
    Why it ranks here
    Cracked or loose hoses are a common small-leak source in general guidance.
    What would change this
    Rises if smoke escapes at a hose.
    How to test the vacuum hoses and intake leaks

  4. Leaking or contaminated charcoal canister

    Possible — needs testing
    Why it ranks here
    GM has a bulletin for a canister weld that leaks and sets P0442.
    What would change this
    Rises if smoke escapes at the canister body.
    How to test the evap charcoal canister

  5. Filler neck or cap seat not sealing

    Possible — needs testing
    Why it ranks here
    GM has a bulletin where a rolled rubber insulator at the filler neck stops the cap sealing.
    What would change this
    Rises if the rubber around the filler neck is rolled over.
    How to test the fuel (gas) cap

  6. Purge valve leaking or not opening when commanded

    Possible — needs testing
    Why it ranks here
    VW lists P0442 among the codes that can involve the purge valve.
    What would change this
    Rises if the purge valve passes vacuum when commanded closed.
    How to test the evap canister purge valve

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Remove and refit the fuel cap. Check it is a factory or OEM-equivalent cap, that it clicks when tightened, and that its seal is not cut, cracked or rolled.

    Low risk

    • IfThe cap was loose, missing, non-factory or has a damaged seal

      It meansThe cap is the most likely leak. Tighten or replace it and let the system re-check over the next few days.

      Points to: Loose, damaged or non-factory fuel cap

    • IfThe cap is factory, clicks and the seal looks good

      It meansLook further along the system.

      Go to step 2

  2. Read all stored and pending codes with a scan tool and note which other EVAP codes are present.

    Low riskTool: OBD-II scan tool

  3. With the engine off and cool, look over the EVAP hoses and connectors you can reach at the purge valve, the canister and the filler neck.

    Use cautionTool: flashlight

    Warning:Fuel vapour is flammable. Work outdoors with the engine off and cool, and keep sparks, cigarettes and open flames away.

  4. Have a shop smoke test the EVAP system with the vent side sealed and look for smoke escaping.

    Best left to a shopTool: EVAP smoke machine

    Warning:Shop test. The setup has to match how the system is tested (pressure or vacuum), and fuel vapour is flammable.

  5. Have the shop command the vent and purge valves with a scan tool and check each one holds vacuum with a hand vacuum pump.

    Best left to a shopTool: scan tool with output controls, hand vacuum pump

    Warning:Shop test on the fuel vapour system.

Symptoms

  • Check engine light on, usually with no change in how the car drives
  • Fails an emissions or smog test because of the light or an incomplete EVAP monitor
  • Persistent raw fuel smell around the car Gets more serious: stop and have it checked.
  • Liquid fuel dripping under the car Gets more serious: stop and have it checked.

Compare with: Check engine light came on after getting gas

How to fix

  1. Check the fuel cap is a factory or OEM-equivalent part, then tighten it until it clicks.

    Warning:Engine off, no smoking or flames near the filler.

  2. Look at the cap seal for cuts, cracks or a rolled o-ring and replace the cap if it is damaged.

  3. Stop filling once the pump clicks off the first time. Topping off can flood the canister.

  4. After a repair, drive normally for several days so the monitor can re-run. Clearing codes or disconnecting the battery resets readiness, so do it shortly before an inspection only if you then complete a drive cycle.

Parts and cost context

  • Fuel (gas) cap:A factory or OEM-equivalent cap is the cheapest first step. Toyota, for example, says to use only a genuine cap.
  • EVAP charcoal canister:Replace the canister only after a smoke test confirms it is leaking. Labour varies, so get a quote.
  • EVAP canister vent valve:Often mounted near the canister or tank. Labour varies, so get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Chevrolet

  • 2019–2025 · Silverado 1500

    Supported by vehicle data

    GM bulletin 23-NA-073 links P0442, P0446, P0449 and P0455 on these trucks to dust plugging the canister and vent solenoid in very dusty use. Silverado 2500 HD and 3500 HD (2020–2025) are also covered. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • 2021–2022 · Trax · LE2

    Supported by vehicle data

    GM bulletin 22-NA-217 links P0442 to a weld leak in the purge canister. Smoke test the canister first. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • 2011–2013 · Cruze

    Supported by vehicle data

    GM bulletin PI0979 says the vent solenoid can leak under vacuum but pass a pressure test, so a normal smoke test can miss it. Malibu, Orlando and some Buick models are also listed. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • 23-NA-073Status unverified

    P0442, P0446, P0455 or P0449 from dust plugging the EVAP canister and vent solenoid

    2019–2025silverado-1500, silverado-2500-hd, silverado-3500-hd · issued · NHTSA MC-11016945

    In very dusty use, dust can get into the canister and vent solenoid and set leak or vent codes. GM prescribes adding an inline filter between the canister and its fresh-air inlet, paid by the customer, and treats the filter as a maintenance item. The same bulletin covers GMC Sierra 1500 (2019–2025) and Sierra 2500 HD/3500 HD (2020–2025); cab-and-chassis (ZW9) trucks are excluded.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 22-NA-217Status unverified

    P0442 from a weld leak in the purge canister

    2021–2022trax · LE2 · issued · NHTSA MC-10231485

    A plastic weld fault in the canister can cause a small leak. Smoke test the canister and replace it if it leaks. The bulletin also covers the 2021–2022 Buick Encore with the LE2 engine.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • PI0979Status unverified

    P0442 from a vent solenoid that leaks under vacuum

    2011–2013cruze, malibu, orlando · issued

    The vent solenoid can leak under vacuum yet seal under low pressure, so a pressure-only smoke test can miss it, and the fault may show only when cold. The bulletin also lists 2012–2013 Buick LaCrosse, Regal and Verano and the 2013 Cadillac ATS.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

GMC

  • 2019–2025 · Sierra 1500

    Supported by vehicle data

    The same GM bulletin (23-NA-073) covers the Sierra 1500 and the 2020–2025 Sierra 2500 HD/3500 HD for P0442, P0446, P0449 and P0455 caused by dust in the canister and vent solenoid. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • 23-NA-073Status unverified

    P0442, P0446, P0455 or P0449 from dust plugging the EVAP canister and vent solenoid

    2019–2025silverado-1500, silverado-2500-hd, silverado-3500-hd · issued · NHTSA MC-11016945

    In very dusty use, dust can get into the canister and vent solenoid and set leak or vent codes. GM prescribes adding an inline filter between the canister and its fresh-air inlet, paid by the customer, and treats the filter as a maintenance item. The same bulletin covers GMC Sierra 1500 (2019–2025) and Sierra 2500 HD/3500 HD (2020–2025); cab-and-chassis (ZW9) trucks are excluded.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Buick

  • 2021–2022 · Encore · LE2

    Supported by vehicle data

    Covered by the same GM canister-weld bulletin (22-NA-217) as the Trax. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • 22-NA-217Status unverified

    P0442 from a weld leak in the purge canister

    2021–2022trax · LE2 · issued · NHTSA MC-10231485

    A plastic weld fault in the canister can cause a small leak. Smoke test the canister and replace it if it leaks. The bulletin also covers the 2021–2022 Buick Encore with the LE2 engine.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Cadillac

  • 2013–2015 · ATS

    Supported by vehicle data

    GM bulletin PIC6030 says that on cars built before 9 Aug 2014, the filler pocket insulator can roll over the filler neck and set P0442. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

    Where it is:Fuel filler pocket

  • PIC6030Status unverified

    P0442 from the filler pocket insulator rolled over the filler neck

    2013–2015ats · issued · NHTSA MC-10112256

    On cars built before 9 August 2014, the rubber insulator in the fuel filler pocket can roll over the filler neck and stop the cap sealing. Reposition the insulator and check the cap seal.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • P0455EVAP system large leak detected

    Same system Common general cause

    Same leak test, larger leak. A loose cap can set either, depending on how badly it leaks.

  • P0456EVAP system very small leak detected

    Same system Common general cause

    P0456 is the next leak size down from the same monitor.

  • P0446EVAP vent control performance problem

    Shares causes Supported by vehicle data

    GM links P0442 and the vent code P0446 to the same dust-fouled vent solenoid on some trucks.

  • P0449EVAP vent valve circuit fault

    Shares causes Supported by vehicle data

    GM links P0442 and the vent circuit code P0449 to the same dust-fouled vent solenoid on some trucks.

All EVAP (evaporative emissions) codes

P0442 questions

Can a loose gas cap really cause this code?

Yes. OBD systems can detect the vapour leak from a cap that is not tightened. After you tighten or replace it, the light should go out by itself once the system re-checks and passes on later drives, which can take several trips.

How long after fixing it will the light go off?

The light only goes off after the leak test runs and passes on several drives in a row, and the EVAP test only runs under certain conditions. It can take days or more of normal driving.

Is it safe to keep driving?

Usually yes, as long as there is no strong fuel smell and no fuel dripping. Most makers advise getting it fixed when it is convenient. A strong fuel smell means get it checked soon, and dripping fuel means stop and do not drive.

Will this code fail an emissions inspection?

In states that test OBD-II, a check engine light that stays on with the engine running fails the test. Clearing the code does not help straight away, because the EVAP monitor then reads not ready until the car completes a drive cycle.

Sources and review

  1. Frequently Asked Questions on On-Board Diagnostics (EPA 420-F-97-003) — US EPA ,
  2. On-Board Diagnostic II (OBD II) Systems Fact Sheet — California Air Resources Board ,
  3. EVAP: The Phantom Emissions Menace (Nissan TechNews, May 2018) — Nissan North America (hosted by AutomotiveTechInfo) ,
  4. OBD Test Reference (rev 8.6) — California Bureau of Automotive Repair ,
  5. What do you mean my car is not ready? — New York State DMV
  6. Recall acknowledgement 17V-088: BMW i3 REx fuel tank vent line may chafe — BMW of North America / NHTSA
  7. Part 573 Safety Recall Report 15V-621 (Mazda 8615J): liquid fuel can enter the EVAP canister — Mazda North American Operations / NHTSA
  8. What To Do With the Check Engine Light (EPA420-F-00-041) — US EPA ,
  9. Toyota Camry Owner's Manual (OM06291U, 2.5L A25A-FKS / 3.5L 2GR-FKS) — Toyota
  10. GM PI0979: P0442 from a vent solenoid that leaks under vacuum — General Motors / NHTSA ,
  11. GM 23-NA-073: P0442, P0446, P0455 or P0449 from dust intrusion into the canister and vent solenoid — General Motors / NHTSA ,
  12. FCA 25-002-15 REV. A: P0455 and/or P0456 from a split purge valve hose — FCA US / NHTSA ,
  13. GM 22-NA-217: P0442 from a purge canister weld leak — General Motors / NHTSA ,
  14. GM PIC6030: P0442 from fuel filler pocket insulator rolled over the filler neck — General Motors / NHTSA ,
  15. VW 20 17 02: EVAP purge valve (N80) diagnosis — Volkswagen of America / NHTSA ,
  16. Driveability Corner, August 2014 (Mark Warren) — MOTOR Magazine ,
  17. Cal. Code Regs. Tit. 13, § 1968.2 — Malfunction and Diagnostic System Requirements (OBD II) — California Air Resources Board (via Cornell LII)
Last reviewed
Written by
Saurabh K.
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