OBD scanner will not connect after engine work.
 

Scanner worked before engine work, and works in other vehicles. 2004 Tahoe 5.3 engine, had new head gaskets and intake manifold gaskets installed. Have power to sensor, can see it in wifi and can connect, however will not connect to device. Wondering if something was not reconnected correctly?

Check the fuses...My guess you don't power to the OBD II port

When I plug in the wifi OBD module, I get a light showing it has power. When I connect to the IOS devise I can see the lights flashing as I connect, and when I try any of the OBD apps all the lights flash as the try to communicate, then I receive the timeout or cannot communicate error. Something has changed after the new head gaskets were installed, my guess is with the ECU. I just don't know what to test or check.

head gaskets replacement isn't the cause so we can move away from that. I would go to a auto parts store and see if their hand held scanner will operate on your car. If it does then I would suspect you wifi module has bit the dust. If you were in my neck of the woods I would see if my EFI Live V2 scanner would communicate. Hopefully you will be able to get it figured out.
On EDit: What device are you using to connect to the OBD II Port?

having same issue on a 2003 Suburban. OBD scanner works on all my other vehicles. just not this Suburban. Device shows it has power. not sure whats wrong

found my problem was Apple IOS software. After software update to 11.2.6 now works on tahoe.