EngineLightCodes
Powertrain code

P0456 EVAP System Leak Detected (very small leak)

Severity
Not urgent
Typical repair cost
$20–$500
Do it yourself
Possible, medium
Shop time
0.2–3 hours

The car found a tiny leak in the system that traps gasoline vapor from the fuel tank. The most common cause is the gas cap. It doesn't affect how the car drives.

How the engine computer detects it

The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. P0456 reports a very small leak of 0.020 in (0.5 mm), as CARB requires. Ford uses the engine-off natural vacuum test: after switch-off the closed system must build at least about 190 Pa pressure or 125 Pa vacuum, judged statistically. Saab's Bosch ME9 also tests with the engine off for up to 45 minutes; VW and Audi use a leak detection pump. GM reports this leak size as P0442 instead. The code often appears only after many trips and depends on the weather.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

  • Check engine light on (possibly a check fuel cap message)
  • Possibly fuel smell
  • EVAP readiness or emission inspection not passed

Common causes

  1. Fuel cap seal worn or cap not clicked in Most likely
  2. Purge or vent valve not sealing Possible
  3. Porous hoses or O-rings, hairline crack in canister or filler neck Possible
  4. Leak detection pump itself leaking (VW/Audi) Less likely

How to diagnose P0456

  1. Remove the gas cap, check the rubber seal for cracks, and tighten it until it clicks. A new cap is inexpensive and worth trying first.
  2. Clear the code and drive for a few days. The system needs several drive cycles to retest.
  3. If it comes back, have a shop do a smoke test of the EVAP system. It finds leaks too small to see.
  4. Common leak points are the purge and vent valves, the charcoal canister and the filler neck.

Vehicles that report P0456 most

VehicleYearsReportsMedian miles
Ford Focus2012–20182962k
Jeep Grand Cherokee2004–20191040k
Ford Escape2010–20201083k
Ford Edge2011–20221075k
Ford Fusion2010–2020946k
Mercedes-Benz AMG E552004–2005490k
Ford Mustang2013–20164—
Toyota Corolla2004–2007345k
Mercedes-Benz E3502006–2007387k
Volkswagen Passat2006–2015367k

Counts of owner complaints to the NHTSA that mention P0456 (165 in total), not failure rates: popular models get more complaints simply because more of them are on the road. Models with fewer than 3 complaints are left out.

Reading the code

P
Powertrain
0
Generic (SAE) code
4
Auxiliary emission controls
56
Specific fault

Questions drivers ask

Can I drive with code P0456?

Yes. This code has no effect on driving or safety. In states that scan the OBD system, it will likely fail an emissions inspection until it's fixed.

Will my car pass an emissions inspection with P0456?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Will P0456 clear by itself?

The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.

Can I fix P0456 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.

Often reported together

Codes that owners mention in the same NHTSA complaints as P0456. They can point to a shared cause, so it's worth checking them together.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.