P04DF: EVAP System Purge Control Valve A Performance/Stuck Open

What does P04DF mean?

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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

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

Common causes

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

Likelihood is a general estimate across vehicles; your make and model may differ.