no reading from test port? can I test - test port?

Ok, so I took my car to autozone the other day to get the codes for my CEL, as it's been on for some time now.

the machine could not communicate with the computer-
tried another autozone, and got the same results.. I pulled the diagnostic port out to check the pins, and they all look OK, and in place.. I don't have VAG COM right now, and was wondering if there is a way to check the test port? is there a way to pull the codes manually?

the car is a 96 TDi passat wagon..

Cheers,

Percy.

It is only possible to get the codes using a scanner.

question for ya: do you have an aftermarket stereo, or is it the original one?

Reason for asking: Aftermarket stereo which is not installed properly (VW-specific issue) can interfere with the "K-line" which is the communication wire, which will prevent any scanner from working.