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.