App note from Vector on three commonly encountered high speed CAN physical layer problems – bus termination, signal levels, and ground. Link here (PDF)
Determining the exact cause of a CAN problem is not at all simple.
Is the problem in hardware or software? Is the problem on the circuit board or on the CAN network wiring?
Sometimes the problem may not be at the module level – perhaps the cause is up at the system level.
This application note discusses methods used to investigate serveral of the more common CAN Physical Layer problems typically encountered when debugging high-speed CAN.