Tapping into a bus


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Ok, so not all of those busses you want to talk to are on the OBDII port. Maybe you have a VW that uses a 'CAN Gateway' which is almost like a firewall. Well no worries, you just tap the two CAN wires directly into the bus. We've done this on a VW right at the boot between the driver door and the body so you don't even need to disassemble anything.

Refer to your vehicles wiring diagrams to identify the location of the CAN network you want to connect to. Sometimes even a Google search will yield some great info. Usually the two CAN lines will be twisted together to equalize noise on the lines but this is not always the case.

CAN Basics

Let's talk about the CAN basics first. Here is a simple CAN network setup:

For more in depth CAN info see this great blog post from Cowfish Studios.

This network is terminated at each end with 120 ohm resistors. To join the network all you need to do is connect CAN HIGH and CAN LOW lines of the CANBus Triple to this existing network. Lets use Bus 1 for this example. We will assume the CBT is powered either by a 12vcd input from the vehicle, or via the USB cable from your computer.

Lets wire it up. Connect Pin 3 (CAN Low) of the CBT harness (Rainbow flat cable supplied) to the CAN High line of your vehicle. Then connect Pin 4 (CAN Low) to the CAN Low line of your vehicle.

You might need to connect a common ground line as well depending on your vehicle. Just run a line form Pin 1 of the CBT harness to the body of your vehicle or to Pin 5 on your OBDII port on your vehicle.

Settings on the CANBus Triple

Now you need to configure the bus speed. Fear not! The CBT will detect the bit rate of this network for you. Assure your car is on and the bus is active or the auto detection will not succeed.

See the quick start guide for auto rate detection and packet logging info.