Sealey vse953 catalytic converter back pressure test kit sealey vse953 p this test kit from sealey is used to establish the working condition of the catalytic converter and silencer by measuring the relative back pressure of the system simply connect into the exhaust system using either of the two oxygen sensor dummy adaptors supplied in the kit p p gauge features a colour coded scale for easy diagnosis and reads both pressure and vacuum so can be used on other areas of the vehicle allo