Some standard OBD 2diagnostic tool is not able to work with VW vehicles but special diagnostictool for VW works.
If your VW is OBD certified, they should be compatible with universal OBD 2 diagnostic tool, but the communication protocol should be thecorrect one.
All VW, Audi, Skoda, SEAT vehicles, no matter it is OBD certifiedor not, they are compliant with VAG diagnostic tools, but the test data is not provided by OBD and the communication protocol is not OBD compliant. VAG group has their own protocol,said always KWP 1281.
So if you are not able to use a standard OBD ii diagnostic tool on VW vehicles, it is reasonable and not means that there is problem with the OBD diagnostic tool.