P0446 fault code: Evaporative Emission System Vent Control Circuit

P0446 means “Evaporative Emission System Vent Control Circuit” — an auxiliary emission controls fault in the powertrain.

Can I DIY?

Professional-only boundary. Read P0446 from the driver's seat; do not go under the car to find the vent valve.

This is the conservative boundary from the reviewed code record. This page has no frozen site-wide safety grade, so it does not publish a repair route.

What to tell the garage about P0446

Do not drive until checked. The computer has flagged the electrical circuit for the EVAP vent control, the valve that lets the charcoal canister breathe to atmosphere. This is a vent-circuit fault, often near the tank, not a purge-flow reading.

Take these reviewed, code-specific details with you. They help the garage confirm the fault without turning this page into a repair procedure.

  • Evaporative Emission System Vent Control Circuit: Registration number
  • Evaporative Emission System Vent Control Circuit: Exact code P0446 and any companion EVAP circuit codes
  • Evaporative Emission System Vent Control Circuit: Whether the engine management light is steady or flashing
  • Evaporative Emission System Vent Control Circuit: Condition of the fuel filler cap and flap from an outside view
  • Evaporative Emission System Vent Control Circuit: Do not ask the garage to 'just clear the light' without a vent-circuit test
P04xxAuxiliary emission controls
MOT fail riskif the warning light stays on

What does P0446 mean?

P0446 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 Vent Control Circuit”. The code itself tells you which circuit or system tripped the fault — not always the exact part that failed.

Will P0446 fail an MOT?

A warning lamp left on for a vent-control circuit fault is a Major MOT defect until the engine management light stays off after repair. Finding the vent valve is not part of the MOT test you can substitute at home.

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.

Related guides

Car diagnostic test cost: compare the scopeUK booking marketplaces currently publish diagnostic averages of about £52–£65. Engine management light on: steady or flashing?A steady engine management light means the computer has stored a fault. Drive with caution and get the code read. A flashing light is different — stop when it is safe.
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

P0446 — quick answers

Is it safe to drive with P0446?

Do not drive until checked. We have no verified driving guidance for P0446. Treat as do not drive until checked. Do not raise the car to hunt for a vent valve by the tank.

Will P0446 fail my MOT?

A warning lamp left on for a vent-control circuit fault is a Major MOT defect until the engine management light stays off after repair. Finding the vent valve is not part of the MOT test you can substitute at home.

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.