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?

  • Also you "have a truck" or "heavy truck" in the title?
    – Solar Mike
    Commented Jan 12, 2018 at 11:39
  • sorry for beeing not precise enouth. i mean Heavy Truck.. Like a regular european Zugmaschiene.
    – Lanard
    Commented Jan 15, 2018 at 8:00

2 Answers 2


There are readers and readers - some readers will read many cars, some have to be tailored to specific makes (such as the one I had to get for my car).

The professional readers have "character" cards to give the reader the correct info for a particular manufacturer.

A reader such as for a VW caddy will not necessarily work on a Jaguar or a Toyota... Which probably explains your problem.

  • Thank you for the Answer. I know what u means. But I don´t think this is part of the problem. I don`t use such readers. I have a device that can read and Write basic Can. So I can write the messages by myself. This means I have to decode the values by myself like described. There are enough pages that describe OBD2 on Can so this is not such a bit of a problem. The only thing. And OBD2 is standard, this means that Car and Truck OBD2 should be the same. But they don´t. The car answers on this standard request but the Heavy Truck not.
    – Lanard
    Commented Jan 15, 2018 at 8:38
  • I think you will find that part of OBD2 is standard as you say, BUT each manufacturer can, and has, supplemented the standard codes with their own versions which give them more detail - for testing etc. This may mean that a standard code which works on a car for you may not be implemented on the truck as the manufacturer has not used that code but replaced it with a « private » code number with extra detail...
    – Solar Mike
    Commented Jan 15, 2018 at 8:47

EOBD (Heavy trucks in europe may not be EOBD compatible but have OBD2, yes. ) Meaning that for passenger caars, by law, they need to use same ports to be compliant but not for trucks over 8 people or 2500 kg

The EOBD (European On Board Diagnostics) regulations are the European equivalent of OBD-II, and apply to all passenger cars of category M1 (with no more than 8 passenger seats and a Gross Vehicle Weight rating of 2500 kg or less) first registered within EU member states since January 1, 2001 for petrol (gasoline) engined cars and since January 1, 2004 for diesel engined cars.[12]

For newly introduced models, the regulation dates applied a year earlier - January 1, 2000 for petrol and January 1, 2003 for diesel. For passenger cars with a Gross Vehicle Weight rating of greater than 2500 kg and for light commercial vehicles, the regulation dates applied from January 1, 2002 for petrol models, and January 1, 2007 for diesel models.

The technical implementation of EOBD is essentially the same as OBD-II, with the same SAE J1962 diagnostic link connector and signal protocols being used.

With Euro V and Euro VI emission standards, EOBD emission thresholds will be lower than previous Euro III and IV.

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