Here's a guide on how to test an ABS (Anti-lock Braking System) sensor:

Locate the ABS sensor

Usually found near the wheel hub or brake rotor
Typically one sensor per wheel in modern vehicles

Visual inspection

Check for physical damage, corrosion, or contamination
Ensure the sensor is properly mounted and aligned

Resistance test

Disconnect the sensor from the vehicle's wiring harness
Use a multimeter set to ohms
Measure resistance between the sensor's terminals
Compare the reading to the manufacturer's specifications

Output voltage test

Reconnect the sensor
Set the multimeter to AC voltage (usually mV range)
Raise the wheel off the ground
Spin the wheel by hand
Check for a fluctuating voltage reading (typically 50-700 mV)

Scan tool method

Connect an OBD-II scan tool to the vehicle
Access the ABS system data
Check for any stored fault codes
Use the live data function to monitor sensor output while driving

Oscilloscope test (advanced)

Connect an oscilloscope to the sensor wires
Spin the wheel
Observe the waveform pattern
A good sensor should produce a clean sine wave

Magnetic field test

For passive sensors, use a small magnet
Move the magnet past the sensor tip
This should produce a voltage reading on a multimeter

Tone ring inspection

Check the tone ring for damage or missing teeth
A damaged ring can cause erratic sensor readings

Wiring harness check

Inspect the wiring between the sensor and the ABS control module
Look for cuts, frays, or pinched areas

Replacement test

If all else fails, try replacing the sensor with a known good one
This can help determine if the issue is with the sensor or elsewhere in the system

Want to get more detailed information about that, you can visit this blog: How to Test ABS Sensor?