Long story short I am looking to build my own CAN bus interface to connect features of an after market stereo and retain parking sensors - there are a few after market products but I have tried a couple and frankly they leave a lot to be desired so I am going to build and program my own!

I'm only at the start of this project so first thing is to interface and analyse the CAN bus.. I have successfully connected and can pull data through the OBDII connector under the drivers side, but if I connect to the CAN bus wires at the stereo harness I get nothing..

Following the wiring diagram I believe the CAN High and CAN Low at the diagnostic port should be connected to the same wires that present at the stereo harness connector, they are one and the same wire, connected through-out the car, the terminators are at the central junction box and instrument cluster, so if I put a multi-meter on the diagnostic socket wire and the same stereo harness wire I would expect a close circuit, no resistance, same wire.. For each respectively on CAN H and CAN L.

However I am getting about 6.7kOhm on both, this is with the car idle, I haven't and don't really want to put an ohm meter across the bus when things are running.

The thing is, with the factory stereo connected the parking aid noises etc all work OK, and the only thing feeding the factory stereo on that harness is +ve BATT, GND, speakers, ANT power, SWC GND and OP, and the CAN bus - it HAS to be the CAN bus that makes the parking noises work.

So I don't know why I'm getting this weird resistance, and the CAN bus wires with a simple transceiver and control module at the diagnostic port give data, at the stereo harness give nothing.

Any pointers would be really appreciated.. The electronics I am good with, the CAN bus is a completely new beast that I have only been playing with a few days now so really out of familiar territory.

#UPDATE..

Feel like such a newbie..

There is a HS CAN bus (high speed, engine management, important stuff)..

AND..

MS CAN bus (medium speed..?, less important/non-critical stuff)..

Using exactly the same transceiver but initialising the bus at the lower speed.. data! beautiful amounts of HEX data!

Happy days!

From my findings, looooong time ago, you will find parking sensor information on ID 0x188.
Byte 0 - 0x03 - means parking off, 0x73 - when parking sensor are on
Bytes 1 to 7 - sensors information.

Thank you so much.. That is great information.

Would love to take a sneak peek at a full LR tech table of all codes.. Alas, time for some spreadsheet workouts and figure it out myself