Powertrain, generic · Auxiliary emission controls

P04DF EVAP System Purge Control Valve A Performance/Stuck Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Purge valve A is the main EVAP purge valve between charcoal canister and intake manifold (on turbo engines the low-load path); its electrical circuit faults are P0443, P0458 and P0459. No manufacturer document available to us uses this code; the description follows GM's comparable check P0496, Subaru's valve B counterpart P04AE and CARB's purge flow requirement. P04DF means valve A does not react as commanded or lets vapour through when closed: with the system sealed and the valve not driven, vacuum must not reach the tank. Intake vacuum then draws vapour all the time – rich mixture and hard starting after refuelling are typical.

Likely causes

Purge valve A leaking or stuck open (charcoal dust or dirt on the seat)
Canister broken down, charcoal dust in the valve
Tank pressure sensor giving a wrong signal
Hoses swapped or wrongly routed

Symptoms

  • Check engine light on
  • Hard starting or stumbling idle right after refuelling
  • Rough idle, rich fuel trim

Repair estimate

DifficultyEasyDIY possible
Parts and labour€40–250
Time0.3–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

evap purge valvecharcoal canisterfuel tank pressure sensorengine control module

Related codes

P04E0P0496P0441P0443P04AEP0458

References: saabwisonline.com, static.nhtsa.gov, law.cornell.edu.