P0456 Evaporative Emission System Leak Detected (Very Small Leak)
P0456 is a generic OBD2 powertrain code. It means “Evaporative Emission System Leak Detected (Very Small Leak)” — the same on every make and model, because the definition comes from the SAE J2012 standard rather than from the carmaker.
Ask the AI about P0456 on your car- System
- Powertrain (P)
- Code type
- Generic (SAE)
- Range
- P04xx
- Urgency
- Low
What P0456 means
The computer sealed the EVAP system and watched its pressure, and found a small leak (P0442 — about the size of a 1 mm, 0.040″ hole) or a very small one (P0456 — about 0.5 mm, 0.020″).
Symptoms
- Usually nothing but the lamp
- A failed emissions inspection
Most likely causes
- A gas cap with a worn or hardened seal
- A cracked hose or loose clamp in the EVAP lines
- A purge or vent valve that doesn’t fully seal
- A hairline crack in the canister or a rusted filler neck
What to check first
- Start with the cap: inspect the seal and replace the cap if it’s cracked or hard
- Check the hoses around the canister and the filler neck
- Leaks this small are hard to see — a smoke test is the reliable way to find one
Can I keep driving with P0456?
Safe to drive — fix it when convenient
Yes. Nothing about how the car drives is affected; fix it before the next emissions test.
How P0456 breaks down
Powertrain. Engine, transmission, fuel and emissions — the codes behind the check engine lamp.
Generic code: defined by SAE, the same on every make.
Auxiliary emission controls.
The specific fault within this range.
Where to look: Auxiliary emission controls
The systems that clean up exhaust and fuel vapor: exhaust gas recirculation (EGR), secondary air injection, catalytic converter monitoring, the evaporative emissions (EVAP) system with its purge and vent valves — plus exhaust temperature sensors, the particulate filter and some cooling-fan circuits.
All P04xx codes →Ask the AI about P0456 on your car
Pick your car and ask — the assistant takes your make, model and engine into account. Ten questions a day, free, no sign-up.
The assistant is answering…
That's 10 for today
The free web limit resets tomorrow. In the Brimly app the assistant knows your specific car — its real mileage, fuel log, and service history.
Requires iOS 18.1 or later. Free to download, with optional in-app purchases.
The conversation is stored only in your browser — we don't keep it on our servers.
Read and clear P0456 on your iPhone
Brimly reads stored, pending and permanent codes through a Bluetooth LE or Wi-Fi OBD2 adapter, explains each one offline from the same 2,693-code dictionary as this page, and clears them once the fault is fixed — each clear goes into the car’s service history with the codes it removed. OBD diagnostics are part of Brimly Forever, a one-time purchase; the PRO assistant explains a code for your exact car.
Requires iOS 18.1 or later. Free to download, with optional in-app purchases.
Frequently asked
What does P0456 mean?
P0456 is a generic OBD2 powertrain code. It means “Evaporative Emission System Leak Detected (Very Small Leak)” — the same on every make and model, because the definition comes from the SAE J2012 standard rather than from the carmaker. The computer sealed the EVAP system and watched its pressure, and found a small leak (P0442 — about the size of a 1 mm, 0.040″ hole) or a very small one (P0456 — about 0.5 mm, 0.020″).
Can I drive with P0456?
Yes. Nothing about how the car drives is affected; fix it before the next emissions test.
What causes P0456?
A gas cap with a worn or hardened seal; A cracked hose or loose clamp in the EVAP lines; A purge or vent valve that doesn’t fully seal; A hairline crack in the canister or a rusted filler neck.
How do I clear P0456?
Fix the cause first, then clear it with any OBD2 scanner or app. Once the fault is gone the car also clears it on its own: the check engine lamp goes off after the self-test passes on three drive cycles in a row, and the stored code ages out after about 40 warm-ups. Clearing without a repair only hides it for a while — and resets the readiness monitors an emissions inspection looks at.
Is P0456 the same on every car?
Yes. P0456 is a generic SAE J2012 code, so its definition is identical on every make and model. What differs is the cause behind it and the repair procedure, which depend on the engine — that’s why the assistant on this page asks for your car.
Guides
Definitions: the generic SAE J2012 codes from Brimly’s offline dictionary (data version 2026.09). Causes and advice are general guidance for all makes — the service information for your car has the last word.