When I plug my OBD 2 reader into the port, the reader will read all codes, if any, sometimes. Other times it has trouble linking with the ECU, I presume, and won't read anything. The reader says " linking error". What could cause that problem? Thank you in advance for your help.
Trying to properly troubleshoot an issue like this is next-to-impossible over the Internet. You could have a DLC connector problem, a hardware fault with your scan tool, a timing issue with the buss, etc.
While the XLR is OBD II compliant for reading power train codes, a Tech 2 is your best bet, and does a whole lot more.
Have you used your scan tool without any problems on another car?