Evaporative Emission (EVAP) Natural Vacuum Leak Detection (NVLD) Module: Notes

The NVLD module is located in the EVAP canister vent hose, under the vehicle. Battery voltage (VBAT) is supplied to the NVLD module to allow EVAP system diagnostics to run after the ignition is turned OFF. The NVLD module electrical connector also incorporates a communication (NVLD) circuit and a ground (GND) circuit between the NVLD module and the PCM.

Internal to the NVLD module is a normally open vacuum switch (closes with vacuum), a normally closed vacuum relief valve (opens with excessive vacuum), a normally closed pressure relief valve (opens during refueling), an internal ambient air temperature sensor and a timer. The NVLD module completes a series of checks to confirm the integrity of the enhanced EVAP system components in the engine running state and the ignition OFF state. When the ignition is turned ON and the engine is running the NVLD module sends the information stored during the ignition OFF tests to the PCM.