I truly adore VCDS for all the diagnostic options it has, but I am having some problems when it comes to testing the injection pressure in common rail. When it's really cold and the engine doesn't start, VCDS won't show any fault codes and parameters it shows aren't that accurate. Are you using any other, more precise tools ? I consider getting the http://auto-testers....on-analyzer.htm  Personally, I haven't got anything from them and I'm still hesitating. Have you heard anything of their equipment?  http://auto-testers.com/ ?  How do you deal with these problems, is VCDS enough for you or you are using some other devices as well? Looking forward to your opinions guys .

VCDS reads the values/parameters that the ECU has. No diagnostic tool (including dealer diagnostics) that connects via the diagnostic socket will show anything different.

If diagnostics don't give you what you need, you need to revert to specialist direct measuring tools.