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.
Natural Vacuum Leak Detection (NVLD): Notes
Natural Vacuum Leak Detection (NVLD) is a passive diagnosis system for the fuel evaporation system.
The NVLD requires a longer engine cutout time in order to identify a leakage. Therefore a short leakage test is not possible. Depending on the ambient conditions, the diagnosis normally requires that the engine is off for between 6 and 12 hours.
The California Air Resources Board (CARB) has issued a regulation. This regulation states that an overall leakage in the fuel evaporation system exceeding 0.51 mm (0.02 inches) must be identified.
The fuel evaporation system must therefore meet the following requirements:
- Sealed against the environment
- Identify and display a leak
The leak diagnosis on the fuel tank for petrol engines is a legal requirement in these countries.
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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.