📖 What It Does
Stops gasoline vapors from escaping at the gas cap, fuel tank, or fuel lines. Reduces smog-forming emissions and recovers fuel that would otherwise be wasted.
⚙ How It Works
Vapors from the gas tank vent into a charcoal canister where the carbon adsorbs hydrocarbons. When the engine is warm and at cruise, the purge valve opens, engine vacuum pulls the stored vapors into the intake manifold, and they are burned with the air/fuel mix. A vent valve opens to allow fresh air to flow through the canister during purge.
⚠ Symptoms When It Fails
Most common symptoms: check engine light with P0440-series codes, gas smell near the rear of the car, fuel cap warning, or rough idle when the purge valve sticks open. Loose gas caps and cracked purge valves are the top causes. See full symptom guide.
💰 Replacement Cost
Common repairs: $0–$600. Tightening a gas cap is free. A new purge valve runs $150–$300. Replacing the charcoal canister is $300–$600 at most shops. See canister cost.