I’m getting a lower voltage on one speed sensor than the other 3.

The 4 amigos are tripped by this corner.

What generally causes the low voltage?

I’m going to swap the front two sensors to see if the problem follows.

But could this be an ECU issue? Is this voltage low enough to be the issue (I assume it clearly is).

 

The voltage the nanocom reads is the average voltage from a square waveform, so it pulsing from lets say 4.4 volts to zero volts. It will be good to swap it left to right, but I suspect you have a piece of trash on the magnetic sensor face reducing the voltage. Remove the sensor and clean the face, see if it correct the problem. I usually do this with the cdl unlocked, both front wheels off the ground on jackstands or lift, put vehicle in drive and allow axle to turn very slowly. In this way you can test voltage without putting entire brake assembly back on and if you need to you can swap in new sensor or swap left to right and test before reassembly.