I initially thought this info might just be for the Tech heads out there, yet it really has a far reaching audience i.e. More often than not we all need our brakes to work at their best!
Vehicle came ABS light on dash? (Anti-brake skidding). Diagnostic checks were made, sensor readings on test drive all proved normal.
Upon closer inspection, some very small debris was seen on the wheel speed? The sensor is magnetic and relies upon notches in the inner wheel hub to induce a frequency/voltage back the ABS module and then it can see individual wheel speed calculations. The module uses this to determine where to prioritise the brake fluid and apply and stop yr wheel skidding so you pull up significantly earlier.
Anyway this vehicle was flood damaged 5 years ago in storm water.. hence the very rusty brake rotors are now breaking down and iron deposits are falling onto the sensor and upsetting the ability to effectively brake the vehicle, especially when really required!