P0446: Evaporative emission system vent control circuit

How to read it

P0446 is one of the standard OBD-II trouble codes stored when the check engine light comes on. SAE J2012, the standard that defines the codes, names it “Evaporative Emission System Vent Control Circuit”; a generic list of OBD-II codes gives the same name.

Also searched as: code P0446, P0446 code.

What the evaporative system monitor checks

The federal rule requires the system to detect any fuel vapour leak at least as large as one caused by a hole 0.040 inch across, and an absence of purge air flow from the evaporative system.

What the manual says to do

Ford’s F-150 manual says that if the indicator stays on, the vehicle should be serviced at the first available opportunity, and that continued driving with it on can mean higher emissions, lower fuel economy, rougher running and more costly repairs.

How the light goes out

Under the federal rule, the check engine light may go out once the fault has not come back during three trips in a row in which its monitor runs without finding it. The system may erase the stored code if the same code has not been registered again in at least 40 engine warm-up cycles.