Powertrain, generic · Auxiliary emission controls

P04B1 Refueling Vapor Control Valve Circuit Low

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). P04B1 means the control wire is shorted to ground, so the valve is permanently energised. With a normally closed valve the tank is then always connected to the canister: daily evaporation loads the canister and the tank cannot be sealed for the leak test. 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

Control wire chafed against ground (underbody, tank area)
Valve coil shorted internally
Moisture in the connector
Driver in the control module

Symptoms

  • Check engine light on
  • Possibly fuel smell
  • EVAP readiness not set

Repair estimate

DifficultyMediumDIY possible
Parts and labour€50–400
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

P04B0P04B2P04B3P2418

References: law.cornell.edu, patents.google.com, gsi.ext.gm.com.