Powertrain, generic · Auxiliary emission controls

P04B3 Refueling Vapor Control Valve Performance/Stuck Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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. Plug-in hybrids and range extenders with a sealed, pressurised tank have an electric valve in the vapour line between tank and canister. It is normally closed and opens before refuelling, so that the tank is depressurised – the filler flap is only released then – and refuelling vapour reaches the canister (Ford patent). P04B3 is the function check: with the valve commanded closed, tank and canister must not equalise their pressure; if the tank pressure follows the canister, for example during purging or the leak test, the valve is stuck open. Ford checks its comparable tank isolation valve under P2450 via the pressure ratio between tank and canister. Daily evaporation then loads the canister, which hybrids with little engine running time cannot purge enough. No manufacturer document available to us uses this code – Ford reports its tank isolation valve as P2418/P2450 – so the description follows CARB and the component patent.

Likely causes

Valve leaking or stuck open (dirt, wear)
Tank pressure sensor reading wrong
Line at the valve swapped or damaged
Control module software

Symptoms

  • Check engine light on
  • Fuel smell
  • EVAP readiness not set

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–500
Time0.5–2.5 h

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

Parts involved

refueling vapor control valvesealed fuel tankvalve wiringengine control module

Related codes

P04B0P04B1P04B2P2450P0496

References: law.cornell.edu, patents.google.com, fordservicecontent.com.