You need a scanner for that. Simple code readers only read codes in the Engine Computer and sometimes in the Transmission Computer. GM's scanner used to be the Tech 2, but I suspect they have moved on to something newer by 2005 models. Most independent shops go to the aftermarket scanners because they will work on almost all brands of cars. Snap-on is probably the most popular but they are very expensive, and even more expensive to update regularly. "Genysis" is another common brand but I did not use them very much so I am not familiar with everything they can do.
You might consider visiting some independent shops, and even some GM dealers, to see if they are considering upgrading or buying something new. Your offer to buy their old equipment might sway their purchasing decision. Typically shops are stuck with their old stuff, so they make the best of it as long as possible. Buying new equipment and updates for it every year is one of their most expensive business expenses.
Also, ask at any repair shop who visits them each week with their tool trucks. Those guys sell scanners made for their companies that are often very similar to the name-brand stuff. They take trade-ins too but those go fast. You might have to leave your name with them for when they get something in. Those guys have a very definite schedule and visit the same shops each time each week or every other week. Sometimes there is a line of mechanics waiting to buy tools so you might have to wait until the end of their hour when they are heading back to work. (Some shops only allow the tool trucks to show up during lunch hour). Most of the route salespeople are willing to let you come to their homes too in the evening.
The dealerships have gone to internet and computer-based diagnostic equipment now, and I have been told there are aftermarket programs available that do almost as much as the dealer's equipment. I do not know how well those programs work on previous years. You might check on eBay under "Automotive Scanners", but I cannot tell you what is good and what is junk.
Thursday, October 13th, 2016 AT 6:24 PM