Refueling Control Valve

Remove fuel filler cap.
Check air continuity between hose ends A and B.
Blow air into the hose end B. Air should flow freely into the fuel tank.
Blow air into hose end A and check there is no leakage.
Apply pressure to both hose ends A and B [20 kPa (150 mmHg, 5.91 inHg)] using a pressure pump and a suitable 3-way connector. Check that there is no leakage.

Fig 1: Identifying Refueling Control Valve, Recirculation Line And Signal Line
Courtesy of NISSAN MOTOR CO., U.S.A.