Powertrain, generic · Auxiliary emission controls

P04AC EVAP System Purge Control Valve B 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. Purge valve B is a second electric purge valve, usually for the high-load purge line of a turbo engine, which purges to the compressor inlet when there is boost in the manifold (Ford patent). Many makers solve this path with one purge valve and passive check valves instead – Ford tests it as P04F0 – and then have no valve B. CARB requires every purge path to be checked. P04AC means the control wire of purge valve B is shorted to ground: the valve stays energised and open, purging is uncontrolled and the mixture may run rich, especially at idle or after refuelling. No manufacturer document available to us uses this code; the description follows CARB and the comparable purge valve A checks (for GM P0443/P0458/P0459).

Likely causes

Control wire of purge valve B chafed against ground
Coil shorted internally
Moisture in the connector
Driver in the engine module

Symptoms

  • Check engine light on
  • Rough idle, rich mixture
  • Starting problems after refuelling

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 valve bhigh load purge linepurge valve wiringengine control module

Related codes

P04ABP04ADP04AEP0458P0443

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