OBD-Python unable to get VIN number

Question

I am using the library OBD-Python and when I tried to get a VIN number from my vehicle even following the Custom Commands documentation, I received this message:

[obd.obd] 'b'0902': VIN NUMBER' is not supported Date: 2018-07-09 14:48:30.428588 -- VIN NUMBER: None.

def vin(messages):
""" decoder for RPM messages """
d = messages[0].data # only operate on a single message
d = d[2:] # chop off mode and PID bytes
v = bytes_to_int(d) / 4.0  # helper function for converting byte arrays to ints
return v * Unit.VIN # construct a Pint Quantity
c = OBDCommand("VIN",           # name
           "VIN NUMBER",    # description
           b"0902",         # command
           17,              # number of return bytes to expect
           vin,             # decoding function
           ECU.ENGINE,      # (optional) ECU filter
           True)            # (optional) allow a "01" to be added for speed
o = obd.OBD()
o.supported_commands.add(c)
o.query(c)
print('Data: ' + str(datetime.datetime.now()) + ' -- VIN NUMBER: '+str(connection.query(c)))

What I am doing wrong?

Answer 1

Some vehicle manufactures respond with all 0xFF in the bytes. They do this, maybe, to thwart the 3rd party OBD2 scan tools providers that only offer a limited number of vehicles that the tool can be used on, noting that to increase that number requires the purchase of more licenses. By filling the VIN with all 0xFF means that this trick no longer works. In doing this their service centers can use 3rd party OBD2 scan tools without having to keep buying additional VIN licenses as their fleet of vehicle they service increases. Just my thoughts.

Answer 2

You're not doing anything wrong. Almost all commands as defined by SAE J1979 are optional – vendors can chose to implement them or not. In the case of your vehicle, it looks like the vendor decided against it.