If it was on when you picked up the GX (but not when you dropped off) I'd take it back to the shop who did the work. They likely disconnected the battery when key was in ignition... Otherwise you'll have to see a dealer or other independent (w/ the proper equipment) to reset (or test) the system.
Yup, it's probably the drivers seatbelt harness. The buckle part that you plug the seatbelt into. Happened to me. Part is like $45 and it is held in by a bolt and it plugs into the harness under the seat. You just have to order the right color that matches your interior. The there is a bulletin on it. Also a common problem that affected 03-05
I was able to repair my seatbelt harness rather than replace it, the harness was badly worn in one section, and one of the wires had actually broken. Soldiered in a patch so the harness was longer, and it's been good ever since.
The models affected applies to vehicles PRODUCED BEFORE the production change effective VIN as mentioned below JTJBT20X*90173473.
But just to let you know there were few 2004 models also affected, but TSB was released to the 2005-2009 models as many were found that the harness was defective due to a production fault. You could do the replacement, but u still need the tool to clear the DTC faults from its ECM memory once done.
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