A driver reports that ABS activates just before the vehicle stops, but there is no warning light most of the time. Graph all four wheel speeds during a slow stop. Three sensors decrease smoothly to zero while one briefly falls to zero early and then returns. That pattern explains the false ABS event.
Before replacing the sensor, inspect the encoder. Rust under a passive sensor can increase air gap. A cracked tone ring can alter tooth spacing. A magnetic encoder in a wheel bearing can be damaged by incorrect installation or contamination. Bearing play can move the target away from the sensor under load.
The electrical signal can be checked at low speed because that is where the fault occurs. An oscilloscope may show reduced amplitude or a missing section. On an active sensor, verify supply and signal according to the circuit design rather than relying on resistance.
This example shows why testing in the failure condition matters. A parked resistance check might look completely normal.
Figure: Case Study: One Wheel-Speed Sensor Drops Out at Low Speed