according to the DTC code sheet there are 4 faults with this number. All of them related to the canbus circuit.
DTC 2000-12 - CANbus Comm Error VSM
DTC 2000-12 - CANbus Errors (Mazda ECU)
DTC 2000-12 - CAN Tx Failure
DTC 2000-12 - CAN Rx Failure

those yellow and green wires go to all the nodes in the system and all usually return to the vsm so you'll need to check the connections and wiring for corrosion or damage. If no damage is found in the wiring then it is possible that the component is bad, in this case it gives indication of the ecu or vsm.
The possible causes listed are:
A. TERMINATION RESISTOR(S) OPEN CIRCUIT
B. OPEN/INTERMITTENT CIRCUIT ON CAN HI, CAN LO
C. CAN HI AND CAN LO SHORTED TOGETHER
D. OPEN CIRCUIT ON POWER/GROUND TO CAN CONNECTED DEVICES
E. STG ON CAN HI
F. STS/STB ON CAN LO
G. CAN CONNECTED DEVICE FAILURE