I am trying to do a remote tachograph authentication by sending a RemoteCompanyCardReady cantp message to a VDO tachograph on connector C.
The reply message I get is a nack 7f 31 7f which seems to suggest there is no open session. I can't seem to find anywhere how to open the diagnostic session to the tachograph. Also the can id I am using for sending the messages is 18DAEEFB, is that correct? Can anyone give me the byte sequence on the can bus for that?
If you are receiving a response from the device (7F 31 7F in your case), then the CAN ID seems to be correct.
The service which you are trying to send (0x31) seems to be a Routine Control service. Those services usually work in the Diagnostic Session.
According to the ISO, Session Control service is 0x10. So, try to send the request (10 03) to the device. If you receive a positive response (50 01 XX..) then send your required service immediately (within 5 seconds of receiving 50 01).
