Check engine light on but scan tool will not scan.
 

My check engine light came on so I took my truck down to autozone to scan it. They hooked up the scan tool and had me turn the ignition switch to on. The scan tool would not show anything at all (blank screen). They got another new scan tool off the shelf and it did the same? We tried unplugging and plugging back in, checked electrical and all fuses we could find under the hood and at fuse panel. All looks ok. Any ideas?
Thanks in advance

Truck is 1999 F-250 Super Duty 5.4.

I do not have power to the data link connector. What powers it and is there a fuse inline?

hey just a guess but i'll bet your cig lighter doesn't work either... thats what happened to me anyway in my expedition. lucky for me my wife has an 2000exp and i have a 99 f150 everything is basically same so i was able to trial and error with the f150 or i never would have figured it out. the cig lighter and the diagnostic plug are on the same fuse so check that and take out the actual lighter out of the plug hopefully you'll get power. i did

It was 3rd fuse down from the left. Fuse was missing. Put a fuse in and both cig lighter and DLC have power now. Thanks for the help

glad that worked out for ya.... anything to help another ford fan=)