About 2 weeks ago my check engine light came on and i received the p0420, thinking it was the cat or O2 sensors. A few days later after a high octane fill up it went off and was off until 2 days ago, when it came back on. I wanted to get it scanned again to see if it is the same problem but Ive gone to 2 different places and they cant scan to see what the error code is. It seems there is no communication between the scanner and my car. Anyone ever have this?

 

It might depend on the scanners used. The dealer's scanners are more comprehensive than some of the other types of scanners, I have been told by frineds who are mechanics.

 

thanks, do dealers charge a diagnostics fee to get my CEL scanned?

 

Depends on the dealership, but generally yes. I was quoted a flat rate of $65 about 3yrs ago. I declined that and bought my own scan tool.
I heard chain stores like Autozone can lend you a scan tool for free.

 

Possibly the original scan tool connector damaged one of the pins in the vehicle's OBD2 connector.

Personally, I wouldn't trust a parts store "counterman" to touch my car. Often you get what you pay (or don't) for.