OBD2 issues
 

i just purchased an obd2 scan tool and attempted to connect it to my '01 jetta GLI. all i'm getting is a message on the scanner screen: faliure to establish connection. i've tried cycling the ign and all but keep getting the same message. its not the scanner because i connected it to a nissan altima and it linked up with no issues. i went to the web site for the scanner and it did mention that vw has had problems with the scan tool not being able to connect if there has been an aftermarket radio or alarm installed. i do have a pioneer head unit so i'm thinking this may be where the issue lies, but i don't know where to go from here. is there something that needs to be reconnected, bypassed, jumped before the dlc connection will work?