I built a simple Android app that reads in basic car parameters via OBD-II like VIN number and battery voltage. It work nice but I have problems retrieving VIN number from non-German/non-American cars. So for instance in case of Citroen or Fiat one cannot get the VIN number and the returned value is either NULL or UNKNOWN.
Any idea how to solve it? I use the command 09 02 (elm327).
On
0902 is for J1979. This is typical in the US for fetching VIN, as its required by law to be available. As such, European manufacturers don't always implement 'standard' OBD services.
ISO27145 (WWHOBD) is meant to standardize OBD worldwide, and uses a subset of service 22 to get OBD information. Instead of service 01 and 09, there are 22F4 and 22F8.
ISO14229 also has a VIN reference, 22F190, which is separate from the two mentioned above. I've been able to pull VIN for Fiats using this standard.
Not all cars support the 0902 command (mode 9 PID 2) to get the VIN. It is optionally supported. If you send 0900 first, that provides a "bit map" of the supported PIDs for mode 9 on that ECU.