J1850 VPW - How to begin

Hi there!

For the beginning: I have zero knowledge about car hacking.
I bought an android head unit for my cadillac srx 2005. The unit was supposed to retain all the communication going to the oe radio but it doesn’t. The producer than told me that they cant decode anything and simply give me a right canbox mounted behind the radio, because they couldn’t communicate with the modules. I guess it’s all because of the j1850 vpw bus.
My plan is to reverse engineer the warnings which come on the radio, HVAC commands i.e. and make an android app which receives/sends the messages via bluetooth to an interface like M2.
Can you guys please help me begin with it? I am not sure, if I should buy M2 or some other device has better approach for J1850. Maybe 2xM2 to simultaneously send and monitor effects?
Do you know if some sniffing / message filtering software would be helpful?

I hope that you guys can point me in the right direction.

I would start by at least skimming this thread:

I think everything you are looking to do can be done with M2 and the J1850 Arduino library.

You won’t find a step by step guide for this project but it sounds like you’re on the right track.

I’ve been doing it since a week.
Today I tried to connect with my car with my old elm327 USB scanner using a terminal. This worked fine. I found some data being transferred, so I guess that I have to just order a M2. I will keep decoding some simple things like buttons via terminal until it arrives in Poland.