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You'll need a differential comparator, something like what was suggested in [here.](https://forum.allaboutcircuits.com/threads/2-led-logic-probe-for-can-bus.119597/)
![Image_alt_text](https://electrical.codidact.com/uploads/ot0bum4akgg9chtybczrg4ik7u8j)
But I'd look for a proper Canbus Rx and extract that to convert to single ended one shot to pulse for activity.