EngineLightCodes
Powertrain code

P0447 EVAP System Vent Control Circuit Open

Severity
Fix soon
Typical repair cost
$30–$280
Do it yourself
Possible, easy
Shop time
0.3–1.5 hours

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.

How the engine computer detects it

P0447 belongs to the older scheme for the vent valve circuit (P0446 circuit, P0447 open, P0448 shorted), used by Subaru (also in the Saab 9-2X), VW and Nissan; GM reports an open vent circuit as P0449, Ford as P0446. On Subaru the valve is fed from the main relay and switched to ground by the module; if the voltage at the module output is missing or the coil is high-resistance (nominal 10–100 Ω), the code sets after two consecutive drives. The valve stays in its rest position and the leak test cannot run.

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

Symptoms

  • Check engine light on
  • EVAP leak test does not run, readiness not set
  • Usually no change in driving

Common causes

  1. Vent valve connector corroded or off (underbody, splash water) Most likely
  2. Vent valve coil open (resistance outside 10–100 Ω) Possible
  3. Wire to the module or supply from the main relay open Possible
  4. Engine module or its connector Less likely

How to diagnose P0447

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: evap vent valve, vent valve wiring, engine control module.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Reading the code

P
Powertrain
0
Generic (SAE) code
4
Auxiliary emission controls
47
Specific fault

Questions drivers ask

Can I drive with code P0447?

Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.

Will my car pass an emissions inspection with P0447?

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 P0447 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 P0447 myself?

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

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.