On the can bus, a typical message looks like this (but in binary) In my case, with no cluster, I just connected to the orange/black and orange/brown twisted pair coming off T121. By being a "bus", CAN networks aren't point to point but can be tapped in the middle. So the gateway will filter messages coming to and from your transciever. Mk4s with the EDC15 had a gateway in the instrument cluster for the OBD port.
I used the SeeedStudio CANshield and an Arduino Uno.Īlso remember that the CAN bus at the OBD port doesn't offer the same features as the CAN bus between the ECM and Instrument cluster. This is how the RPM signal gets from the ECM to the Instrument cluster in a factory ALH.Ĭonnecting to the CAN bus you need a CAN transciever to read the messages from the bus and a microprocessor to get the message off the transciever and do something useful with them. I don't know the structure of these messages, but the speed over here is similar to logging with a VCDS.įastest, 500kbps.
You have to ask for each piece of data using a standard set of OBD II codes. There's three ways to get data out of the ECM: Tach, water temp, boost, etc, it's all there as a digital value in the cluster. So there's the ECM, full of all sorts of data that we'd love to have looking up at us from the instrument cluster. Here's my example: a 2000 Jeep TJ instrument cluster displaying RPM from the ALH ECM. This thread contains all the Arduino code and other resources I used to make it happen. There's probably a million ways to do this but this is probably one of the easiest if you're like me and not a software programmer.
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