My problem: I try to read data’s from Heavy trucks(40Tonns) via OBD2. This is needed for a research project. I have already read many articles about OBD2 and interfaces for OBD2 like about the ELM interface. Also the Arduino can-bus shield (what I also have and use for monitoring). I know the difference of the voltage (Car:12V Heavy Truck:24V). I use the ICP-Con I7450 for sending and receiving via OBD and Arduino with can-bus-shield for double-check and monitor. I know that I send correct messages because I get answer from a VW caddy where I can test the messages. It is clear that OBD is standardised. So theoretical if I can read from a car I could read from a truck too but I didn’t. These are the messages I tried so far: t7DF80100ffffffffffff #of course wrong because after the length 8 there must be a 02 for the count of bytes in this message that are relevant
t7DF80201000000000000 #correct. The caddy answers by 500kb/s
I know that 7DF means that it asks EVERYONE that can answer.
Explanation as I know:
t7DF | 8 | 2 | 1 | 0 | ff | ff | ff | ff | ff
address | Length of the message | byte length | SID | PID | Filler Filler Filler Filler Filler
but this are the short Identifiers. (11bit). There are also the extended identifiers (29bit).
Also the same message but the identifier is the generic ID in extended form.
But neither on 11 or 29 bit I get an answer from a truck (MAN, Mercedes and Volvo has been tested).
I handle the requests like in ISO 15031 described. The OBD connector of the truck has JUST the pinout for Can (can-High and can-Low),Electric( Ground and +24V), and k-line(k-line and l-line). In some trucks just can. No K-line. i focused on Can to read
I´ve tried every request with 250kb/s 500kb/s and 1000kb/s.
So the precise question is: What is the difference between Car Can and Havy Truck Can? Is there a different protocol?