P0456 fault code: Evaporative Emission System Leak Detected (very small leak)
Last updated · OBDCode UK editorial
Keep driving only if there is no wet fuel, no strong petrol smell in the cabin, and the engine runs normally. Wet fuel or a strong smell means stop.
Can I DIY?
Caution — conditions apply. We do not publish DIY repair or strip-down steps for this code on this page. Read codes and observe only; leave the repair to a qualified garage.
Some checks may be possible for a careful DIY driver with the right tools and a safe place to work. Stop if anything feels beyond your skill or kit.
What does P0456 mean?
P0456 is a generic (SAE standard) powertrain code reported by your car’s engine control unit. It sits in the P04xx block, which covers auxiliary emission controls. The stored description is “Evaporative Emission System Leak Detected (very small leak)”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.
How to diagnose P0456 yourself
- Confirm it is the very-small-leak code: Scan while parked. Record P0456 as current or pending, and whether P0442 (small leak) or P0455 (large leak) is also stored. Note freeze-frame only; do not clear codes to 'see if it comes back' before a garage visit. Stop if: You can see or smell liquid fuel, or the management light is flashing.
Park safely and switch off before locating the socket. Its position varies, so use the vehicle handbook and never force or dismantle trim. - Check the fuel filler cap click-seal: At the filler neck, remove the cap and refit it until it clicks and the seal sits evenly. Look for a cracked cap, a missing tether, or dirt on the seal. Do not force a damaged cap, and do not introduce soapy water into the neck. Stop if: The cap will not click, the neck is damaged, or fuel weeps from the filler.
- Look for wet fuel from standing height: On firm level ground, walk around the car and look from standing height at the filler area and the ground under the tank. Do not jack the car or crawl underneath. Do not run a smoke machine or unplug EVAP hoses. Stop if: You find wet fuel, a drip, or a strong petrol smell inside the cabin — do not keep driving to 'air it out'.
Will P0456 fail an MOT?
An illuminated engine management light is a Major defect at MOT until the lamp stays off. A missing or obviously defective fuel cap can fail in its own right. A very small vapour leak with the lamp off is not a named MOT item.
Before booking your test, check what usually fails on your car: see our MOT pass rates by make and model, built from 33.1 million DVSA tests.
What the MOT data says
No MOT certificate item corresponds to this code; MOT outcome data cannot be shown.
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P0456 — quick answers
Is it safe to drive with P0456?
Drive with care. Keep driving only if there is no wet fuel, no strong petrol smell in the cabin, and the engine runs normally. Wet fuel or a strong smell means stop.
Can I fix P0456 myself?
Caution — conditions apply. We do not publish DIY repair or strip-down steps for this code on this page. Read codes and observe only; leave the repair to a qualified garage. Basic tools only — for example a household socket set, tyre gauge, or a consumer OBD reader.
Will P0456 fail my MOT?
An illuminated engine management light is a Major defect at MOT until the lamp stays off. A missing or obviously defective fuel cap can fail in its own right. A very small vapour leak with the lamp off is not a named MOT item.
Fault-code identifiers are standard diagnostic facts. Their explanations and diagnostic guidance on this site are original editorial summaries, not reproduced SAE wording. MOT defect rules reflect the DVSA MOT inspection manual (2026). This page is general guidance for UK drivers, not a substitute for a professional diagnosis.