Not wanting to assume...
When you say "not locking", do you mean with remote, with interior switch or both?
I think you can get in there with Tech 2 and see what is up at the lock solenoid. When I was playing around, I saw all kinds of useful information like current state (active/inactive), voltage and the ability to issue lock/unlock command. That would help quickly find whether the solenoid itself is actually working. If you can command it to lock/unlock from the tool, then the issue might be with the switch.
Also... Watching the state being active/inactive, you can push the button on the switch and the remote to see the switch/remote is sending lock/unlock commands to the solenoid.
Just being able to see the inputs, outputs, changes in state can go a long way to diagnose what works and what does not.