Evaporative Emission Control System Leak Detected (Very Small Leak)
The P0456 code means the vehicle's onboard diagnostic system has detected: Evaporative Emission Control System Leak Detected (Very Small Leak). This is a minor severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- easy
- Estimated cost
- $8-$30 for gas cap; $150-$250 for a smoke-test diagnosis; $250-$600 for an EVAP hose, vent/purge valve, or charcoal canister replacement; a leaking fuel tank or filler neck can run $450-$3,000
A cracked or loose gas cap causes 60%+ of EVAP codes. This $8 replacement clears P0442, P0455, and P0457 more often than any other repair.
If a new gas cap does not clear it, the leak is somewhere in the EVAP plumbing. A smoke machine finds the exact leak -- a cracked hose, bad seal, or stuck vent valve -- in minutes instead of guessing at parts.
Clear the code after the repair. If the light stays off after 50 miles, you just saved $200+ in shop fees.
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Common Symptoms
- Check Engine Light on
- No drivability symptoms
- Very faint fuel smell in rare cases
Probable Causes (Ranked by Likelihood)
- Loose or worn gas cap seal Very High
- Micro-crack in EVAP hose Moderate
- Small crack in charcoal canister body Low
- Leaking fuel tank pressure sensor O-ring Low
Common Fixes by Vehicle
What techs usually find when diagnosing P0456 on specific vehicles — tap your vehicle for the fix and the exact part:
2007-2018 Jeep Wrangler/Cherokee 3.6L easy (cap) DIY
Small EVAP leak is extremely common on Jeeps. The gas cap seal degrades from dust and UV exposure. Replace with an OE-quality Mopar unit gas cap first. If code returns, check the EVAP purge valve on the intake manifold and the fuel tank filler neck O-ring. Your dealer can confirm whether an open service bulletin or warranty extension applies to your VIN. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 5 min (cap), 1 hour (smoke test + repair)2010-2020 Hyundai Sonata/Kia Optima 2.4L easy DIY
The EVAP purge control solenoid valve (Hyundai) sticks partially open, causing a small evaporative leak. Located on the intake manifold. Test by applying vacuum with a hand pump -- it should hold vacuum when not powered. Also check the fuel tank pressure sensor and the gas cap O-ring for cracks. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 20 min2005-2017 Toyota Camry/Corolla easy (cap), moderate (smoke test) DIY
A small EVAP leak requires a smoke test to find. Common leak points on Toyota are the gas cap seal, the charcoal canister vent valve, and the EVAP hose quick-connect fittings. Replace the gas cap first (Stant) and drive for 2 cycles. If the code returns, a professional smoke test is needed to isolate the leak source. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 5 min (cap), 1-2 hours (smoke test)2009-2020 Subaru Outback/Forester 2.5L easy (cap) DIY
Subaru EVAP systems are very sensitive to small leaks. The most common leak source is the fuel tank pressure sensor seal and the gas cap. Replace the gas cap and check the filler neck for corrosion. If code persists, the EVAP purge valve (Subaru) or the charcoal canister vent valve is the next most likely cause. A smoke test is essential for diagnosis. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 5 min (cap), 1 hour (further diagnosis)Frequently Asked Questions
Is P0456 different from P0442?
Yes. P0456 is a very small leak (around the 0.020 in threshold), P0442 is a small leak (roughly 0.020 in to 0.040 in), and P0455 is a large/gross leak (around 0.080 in or larger). P0456 is the hardest to locate and often requires a professional smoke test.
Mechanics Guide Step-by-step diagnosis, and what most sources get wrong
Step-by-Step Diagnostic Procedure
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Inspect and replace the gas cap as the first step. The seal degrades over time.
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Perform a smoke test with a low-pressure smoke machine. Very small leaks (0.020 in) require patience to locate.
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Inspect all EVAP system connections and O-rings.
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Allow the smoke test to run for a minimum of 3-5 minutes before looking for smoke.
Common Misconceptions / Fact Check
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Commonly claimed"Very small leak" gets read as "not worth chasing," or as the same test P0442 runs.
VerifiedIt is a genuinely tighter test, not a milder version of the same one. The regulation specifies two leak thresholds against precision orifices of stated diameter: a 0.040 inch equivalent and a 0.020 inch equivalent. P0456 is the 0.020 inch test, so a system that comfortably passes the coarser check can still fail this one. That is why P0456 so often appears alone, and why a cap that "looks fine" and seals well enough for the 0.040 test can still be the cause.
Sources 3
This page is built from documented references. Verify against your own service info before repair work.
- California Air Resources Board, Title 13 CCR 1968.2 (2006 final regulation order)§(e)(4.2.2) treats purge flow and leak detection as separate malfunction conditions, §(e)(4.2.1) defines the 0.040 and 0.020 inch orifice thresholds, and §(e)(4.1) excludes purge-valve-to-intake tubing from leak monitoring
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
P0456 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
Commonly Affected Vehicles
- Chrysler, Dodge, Jeep vehicles (Fiat Chrysler products: common gas cap issue)
- Toyota Camry and Corolla
- Ford F-150
- Chevrolet Silverado
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