An OBD2 reader doesn't work for proprietary diagnosis, only regulated/standardized emissions related issues. The example I supplied (Service Now mileage indica

An OBD2 reader doesn't work for proprietary diagnosis, only regulated/standardized emissions related issues. The example I supplied (Service Now mileage indicator, not Check Engine Light) was a very specific one with Porsche in mind. Most post-2004 Porsches have no procedure to reset that indicator without using an official PIWIS ($13000 + subscription, if you can even get one) or reversed Durametric ($250 + illegal if automakers claim their software can't be reversed). Another example of anti-competitive dealer software is "coding." Replacing the headlight control module in a BMW, for example, requires it be "coded" to the car's control systems. Many DIYers and independent shops use straight-up pirated BMW diagnostic tools, because again, the "blessed" way to do so costs thousands of dollars.