Hi Jamie

Depending on what scan tool you have, live data should show the CAN status in ABS. Also, a global scan will confirm if the other modules agree that there is a CAN issue

Next, with the help of a wiring diagram you need to check the CAN network to see you have a short/open circuit.

Maybe you need to get a little history of any other work done. I had an earlier E36 that had an engine change with a different loom fitted that did not carry the CAN wiring to the ABS.

I hope this helps

Simon