Q: Emissions test failed with a new gas cap

Hey there. This may be related to other possible malfunctions in your EVAP system, such as a faulty vent valve solenoid. The EVAP system prevents fuel vapors from the fuel tank from escaping into the atmosphere. The EVAP system collects and temporarily stores the fuel vapors in the charcoal canister. The charcoal canister is filled with activated carbon pellets that can absorb the fuel vapors.

When the engine is running, the fuel vapors are purged from the canister and burned in the engine. The vent control valve (solenoid) controls the flow of outside air in and out of the charcoal canister. When this solenoid is not working properly, this may cause the tank to fail to expel the vapors as it is designed to causing the failed emissions test. If you would like to have the car scoped out, a certified professional from YourMechanic can conduct a comprehensive diagnostic on your car before you take it in for another emissions test.