What did you buy and how cheap was it? Never had a N/A display, but my reader will display "error" if the ignition isn't full on. If there are no codes stored it will display "no codes". It's an old Actron Pocket Scan Model CP9125 unit from the early 2000s and I paid $80 for it. Oddly enough, it's still available on the market today.
I spent 17 bucks on Autel Maxiscan ms300. I know, you pay for what you get!
On my sons truck it worked fine but I cannot retrieve a code from my CTD. I can clear it but instead of a code I get n/a. I have made sure the ignition is all the way on but the result was the same.
I have an I phone so I'm thinking about trying the Engine Link app paired with a WIFI Wireless OBD2 Auto Scanner Adapter Scan Tool for iPhone :
Anyone have any experience with that setup?