Most diagnostic functions do not require internet access, without a connection you will be able to:
Read and Clear Codes
Retrieve Freeze Frame Data
Run Smog Checks
Review Mode 6 Tests
Check MIL Status
Monitor Live Data
The following features will require an internet connection (either WiFi or mobile data)
Repair Reports*
VIN Decoding
Maintenance Schedules
Recalls
Service Bulletins
Sharing Reports
Downloading Firmware Updates
*Note on Repair Reports:
If you read a code and do not have an internet connection, a report can be generated later when wifi/data is available by reviewing the scan report under 'Saved Reports' and then tapping on the code