Fuel Cap Pressure Relief Valve Test

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Set pressure regulator on Tester (16 1 171) fully in "-" direction. Connect tester via compressed air line to workshop/garage compressed air system with a pressure of 116-145 psi. Connect pressure sensor of BMW Diagnosis and Information System (DIS) with a measuring range of 0-50 psi (0-3.5 bar). Select Adapter (16 1 172 or 16 1 173) matching vehicle's filler cap and attach to quick-release coupling of tester. See Fig 1 and Fig 2 .

Fig 1: Identifying Fuel Cap Pressure Relief Valve Tools (1 Of 2)
Courtesy of BMW OF NORTH AMERICA, INC.

Fig 2: Identifying Fuel Cap Pressure Relief Valve Tools (2 Of 2)
Courtesy of BMW OF NORTH AMERICA, INC.
Install filler cap on appropriate adapter. Only the absolute pressure is indicated in the display of the DIS. The current ambient air pressure is already displayed without additional pressurization.
Ensure testing equipment is okay by checking testing equipment for leaks. Select MEASUREMENT function on DIS. Increase pressure by 2.9 psi (.2 bar) with pressure regulator on tester. Using Hose Clip (13 3 010), disconnect delivery line from tester to fuel filler neck. Wait 60 seconds. Read off final pressure value and compare with starting pressure value. If pressure drop is greater than.174 psi (.012 bar) testing equipment is leaking. Check connection joints for leaks.
Check filler cap pressure relief valve by following same test procedure for checking testing equipment for leaks in step 3. Increase pressure by 4.3 psi (.3 bar) with pressure regulator on adapter. If pressure drop is greater than.174 psi (.012 bar), filler cap pressure relief valve is faulty. Replace filler cap.