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.
Evaporation Control System
The evaporation control system (ECS) is used to prevent fuel vapors from entering the atmosphere after the engine is stopped. Vapors that are emitted from the engine and fuel tank when it is stopped are channeled to the canister. When the engine starts, they cannot be immediately purged (drawn into the engine) or the air/fuel mixture will become too rich. However, when the oxygen sensor is operating, it can compensate for the vapors.
The ECS system operates in conjunction with the air switching system. When air injection is shifted downstream, the vacuum signal which keeps the canister purge valve closed is shut off. Engine vacuum draws vapors out of the canister and into the engine, where they are burned. When the engine is stopped, vapors again flow from the engine and fuel tank to the canister. See Figure .
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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.