Scan-anything readers rarely perform a thorough job. We gets loads of people with these devices asking for help because its come back as "marque specific fault code" or similar.
I've done some tests with various scanners on my car with a known EGR, diesel heater sensor, and glow plug faults and only the dealer specific equipment picked up these fault codes and read the live data to show that the parts were indeed faulty.
That's because there is EOBD, a standard by which all vehicle manufacturers agreed to in the 1990s allowing cross communication with a standard 16 pin interface, and there is manufacturer specific. Prior to this different manufacturers used different hardware, software and communication cables, which meant it was very difficult if not impossible non-franchised repairers to interogate controller information. This meant they had a monopoly and led to the EOBD agreement.
EOBD compliance means all manufacturers must allow anyone with a compliant scantool to access data and standard fault codes relating to engine emissions. Manufacturers can offer as much as they like as long as they meet the minimum requirements, so some give more than others. This is a compromise, but better than the pre-EOBD days.
EOBD scantools serve a purpose but if you want to be able to access all information then manufacturer specific is the only way to go.
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