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.
System Description: EVAP: Operation
When fuel tank pressure increases because of heat and fuel vapor generation, evaporated fuel vapors are sent to the EVAP canister where they are stored. When the engine coolant is hot enough, the PCM opens the EVAP canister purge valve to draw the stored fuel vapor in the EVAP canister into the intake manifold to be burned. To regulate the amount of fuel vapor drawn into the engine, the PCM varies the EVAP canister purge valve opening using duty cycle control. When the outside air or other factor cools the fuel tank inside, the fuel tank pressure decreases. The EVAP canister vent shut valve is normally open and allows outside air to enter the fuel tank through the EVAP canister. If there is a system malfunction or blockage in the vent hose, a pressure valve in the fuel filler cap opens and allows outside air to enter preventing system damage. The PCM uses the FTP sensor and EVAP canister vent shut valve to check for leaks in the system. When the enabling conditions are met, the EVAP canister vent shut valve is closed, the PCM monitors for changes in the FTP sensor.
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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.