J1939 CAN_H/CAN_L Common-Mode Voltage: Why Both Lines Moving Together Still Kills Communication

I almost missed it. That’s the part that still bothers me. Two winters ago, a haul truck at a mine site in northern Alberta rolled into the maintenance bay with a dead instrument cluster. The engine ran. The transmission shifted manually. But the dash was dark, and every ECU on the J1939 backbone was throwing Timeout errors like confetti. […]