Sparkfun can shield TEC from 255(bus-off) to 0(error active) manual or automatic?

I am working on a project where i need to analyze the error dynamics of the CAN bus network. I have implemented bus off attack in the CAN bus prototype using Sparkfun CAN bus shield and Arduino uno.
The TEC of the CAN is becoming zero after bus-off. Can some one tell me if the transformation bus-off to error active state is done automatically or do we need to do manually ?
if automatic can anyone please tell how to change the transformation to manual( Arduino code/function)?
if manual can anyone please tell me why i am getting zero TEC after reaching bus-off?

Thanks in advance