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 Emission (EVAP) System
The EVAP system prevents fuel tank gasoline vapors from escaping into the atmosphere. Fuel tank gasoline vapors are routed through charcoal canister into intake manifold for combustion in the cylinders. See Fig 1. Some models use a Bimetallic Vacuum Switching (BVSV) mounted in the engine coolant passage. The BVSV controls the EVAP system in relation to engine coolant temperature.
Various model and engine types will have different evaporative emission system components and operating parameters. For specific EVAP system operating parameters and system and component testing, see FUEL EVAPORATION under EMISSION SYSTEMS & SUB-SYSTEMS in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.
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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.