Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Evaporative Emissions System: Operation
When engine is stopped, fuel vapors flow from float bowl through open solenoid valve down into canister. Vapors from gas expanding in fuel tank pass through vapor separator, 2-way valve and into canister.
The purge line check valve is closed to prevent vapors from rising in the line and entering intake manifold. When ignition is turned on, solenoid valve closes, blocking off float bowl-to-canister passage. The thermal vacuum valve vents control vacuum to air cleaner until engine reaches temperature above 95°F (35°C).
Above the switching point, vacuum is applied to purge control valve. Manifold vacuum pulls fresh air into canister, through the purge line and into intake manifold. This fresh air purges fuel vapors from canister.
Note direction of flow.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.