It varies how they handle the code readers. At AutoZone they said they were not allowed to clear codes but he handed me the reader and I did it while he looked the other way. They were using an off the shelf Actron unit you can buy in their store. At the local Advance they had a special unit also an Actron. He gave me the unit, proper adapter and I had to hook it up and follow the instructions so it could read the codes. It would not display them though. I had to take it back in the store and they hooked it up to a printer and gave me a print out of what the codes were. I then went back out and cleared the code and returned the unit.