P0442 fault code: Evaporative Emission System Leak Detected (small leak)

Last updated 19 August 2026 · OBDCode UK editorial

Can I drive with P0442? — Drive with care

A small evaporative leak does not usually change how the engine runs, but it is not a clean bill of health. Stop if you smell strong petrol or see wet fuel. Book a check before MOT — the engine management light itself is a fail.

P0442 means “Evaporative Emission System Leak Detected (small leak)” — an auxiliary emission controls fault in the powertrain. Drive with care. The petrol-vapour control system has found a small leak. Tank fumes are not sealed as tightly as the self-test expects. This is not an exhaust-catalyst or ignition fault.

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 We do not publish DIY repair or strip-down steps for this code on this page.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.

Caution — conditions applyDIY boundary

ToolsBasic tools only — for example a household socket set, tyre gauge, or a consumer OBD reader.

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.

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Fault code: P0442 — Evaporative Emission System Leak Detected (small leak).
Can I drive: Drive with care. A small evaporative leak does not usually change how the engine runs, but it is not a clean bill of health. Stop if you smell strong petrol or see wet fuel. Book a check before MOT — the engine management light itself is a fail.
Question: What does this code mean for a UK car, is it safe to drive, what are the most likely causes, and what should I ask a garage to check before replacing parts?

For your garage

REPAIR BRIEF — prepared by the owner with obdcode.co.uk
Fault code: P0442 — Evaporative Emission System Leak Detected (small leak).
Drive guidance from obdcode.co.uk: Drive with care. A small evaporative leak does not usually change how the engine runs, but it is not a clean bill of health. Stop if you smell strong petrol or see wet fuel. Book a check before MOT — the engine management light itself is a fail.
Owner’s request: please diagnose before replacing parts, itemise diagnosis time separately, and quote before any work beyond diagnosis.

Carbon monoxide

Never idle in a closed garage to read codes — an open door is not enough. CO is odourless and can kill. Run diagnostics in open air. Headache or nausea with exhaust smell: get fresh air and stop.

P04xxAuxiliary emission controls

MOT fail riskif the warning light stays on

What does P0442 mean?

P0442 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 (small leak)”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

How to diagnose P0442 yourself

Confirm P0442 and other EVAP codes: Scan with the engine off or idling outdoors. Note whether P0442 is current or pending, and whether large-leak, purge, or vent-valve codes are stored with it. Stop if: You smell strong petrol in the cabin, see wet fuel, or the light is flashing (that is not an EVAP-only picture).

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 is seated: With the engine off, open the filler flap. Confirm the cap is present, the seal is not torn, and it clicks on the last turn when refitted. Do not use a smoke machine or pressurise the tank. Stop if: The cap will not seal, you see fuel wetness, or you would need to raise the car to follow vapour lines.

Will P0442 fail an MOT?

An illuminated engine management light is a Major defect at MOT (automatic fail) until the evaporative leak is repaired and the lamp stays off. A small vapour leak does not by itself replace the statutory emissions test, but the lamp will still fail the car.

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.

P0400Exhaust Gas Recirculation Flow P0401Exhaust Gas Recirculation Flow Insufficient Detected P0402Exhaust Gas Recirculation Flow Excessive Detected P0403Exhaust Gas Recirculation Control Circuit P0404Exhaust Gas Recirculation Control Circuit Range/Performance P0405Exhaust Gas Recirculation Sensor 'A' Circuit Low P0406Exhaust Gas Recirculation Sensor 'A' Circuit High P0407Exhaust Gas Recirculation Sensor 'B' Circuit Low

P0442 — quick answers

Is it safe to drive with P0442?

Drive with care. A small evaporative leak does not usually change how the engine runs, but it is not a clean bill of health. Stop if you smell strong petrol or see wet fuel. Book a check before MOT — the engine management light itself is a fail.

Can I fix P0442 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 P0442 fail my MOT?

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.