The vent control valve is associated with the evaporative emission control system. Your vehicle needs an EVAP system to make sure the vapors from the gasoline in the fuel tank don’t make their way outside. Within the EVAP system, there are charcoal canisters which absorb the fuel vapors. Think of these canisters as temporary storage for the vapors.
As vapors are stored, the engine control module activates the vent control valve to allow outside air into the charcoal canister. The fuel vapors within the canister are purged into the engine for combustion purposes. This helps create a more powerful air and fuel ignition. It also keeps the fuel vapors from going outside and polluting the air we breathe.
Most of the time, the engine control module keeps the vent control valve in an open position while the engine runs. The only time when the valve will close is during fuel vapor leak tests. The module conducts these tests to make sure the EVAP system functions well when the engine is shut off. However, if the vent control valve is unable to be activated again, then it means the circuitry to the valve properly has an electrical short. This is indicated by the diagnostic trouble code P0446.
The three main symptoms of this problem are a fuel odor, poor fuel economy, and the Check Engine warning light on the dashboard. Of course, these symptoms are the same as many other problems, but they should at least prompt you to run a diagnostic check. From there, code P0446 will indicate an EVAP system vent control circuit malfunction.
Any kind of problem with your EVAP system like this won’t be of immediate concern. You can still drive your vehicle just fine without any problems. But once you start experiencing the symptoms, you should take action to fix the problem before it gets worse.
- P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
- P0174: System Too Lean (Bank 2)
- P0456: Evaporative Emissions System – Small leak detected
There are several possible causes of a vent control circuit malfunction, such as a damaged fuel tank filler neck, bad EVAP canister vent control valve, loose fuel cap, bad carbon canister, damaged fuel tank, and open electrical connections. A certified auto technician can trace the problem to one of these areas and fix it accordingly.