ABS Sensor : Circuit, Working, Types, Testing, Advantages & Its Applications

The braking systems have changed much smarter and safer with the addition of some electronic controls than ever before. So an Anti-lock Braking System or ABS is found commonly in automobiles. This type of braking system uses an ABS sensor to measure the rotating speed of a car wheel & informs the engine control module of the car regarding the wheel speed. Generally, all the car wheels do not rotate at a similar speed; so the sensor helps in reporting all four car wheels speed to the engine control module to prevent the brakes from locking throughout a stop. This article provides brief information on an ABS sensor, it’s working, and its applications.

What is an ABS sensor?

An ABS sensor is an electronic device that is very significant in modern vehicles because it helps prevent the car wheels from locking up in hard braking and allows car drivers to control their vehicles. These sensors are also called wheel speed sensors. So, the data from this sensor is used by the ABS control module to determine whenever a wheel is about to lock up & apply the brakes to that wheel in a pulsing way. This module can also communicate with the engine control module of the vehicle to change the output of the engine & prevent the car wheels from dropping traction.

How Does ABS Sensor Work?

ABS sensor works simply by monitoring the vehicle’s wheel speed & also its rotation to optimize both brake & traction control through the ABS. These sensors are normally installed at the vehicle’s wheel and they include two main components; a reluctor wheel (or) tone ring and a magnetic (or) hall-effect sensor. Thus, the reluctor wheel is arranged on the axle and it revolves with the wheel whereas a magnetic (or) hall-effect sensor transmits the data to the ABS control module.

Here, the data on wheel speed is very helpful in determining whenever to trigger the ABS & how much force it must apply securely to stop the vehicle without locking up the vehicle brakes. So the information on wheel speed is also provided to engine, navigation, transmission & chassis control systems through data lines with the ABS control unit

ABS Sensor Circuit Diagram

The two 2 wire hall effect ABS sensor circuit is shown below. This sensor has a 12 V power supply wire although no ground directly. In the below circuit, the ground of the ABS sensor can also be the signal wire. This is current regulating, so the amount of flow of current ‘Is’ can be changed simply by the sensor whenever a tooth is passing the sensor. The presence of a tooth can cause either a low or high current & also a gap in between teeth is the opposite based on the design of the sensor.

2 Wire Hall Effect ABS Sensor Circuit
2 Wire Hall Effect ABS Sensor Circuit

The current supplied throughout the resistor in the ABS ECU will generate a voltage ‘Us’ related to the ground like the square wave signal of the three-wire hall effect ABS sensor. In this sensor, the levels of voltage are dissimilar & much lower as compared to the wire Hall Effect ABS sensor due to the low currents. The levels of voltage will be changed from one system to another based on the flow of current as well as the values of the resistor however a clear square wave pattern must be visible.

ABS Sensor Types

There are two types of ABS sensors; active sensor and passive sensor which are discussed below.

Active ABS Sensor

The active ABS sensor is only activated whenever voltage is supplied to this sensor & generates an o/p signal. So these sensors require an additional energy source for operating. These sensors are also known as magneto-resistive as they include a sensing element that is simply connected to a two-pole electric cable or magnetic element. This type of sensor is very efficient as compared to a passive sensor because digital signals are very accurate at slow speeds & detect the wheel direction.

Active ABS Sensor
Active ABS Sensor

Passive ABS Sensor

Passive ABS sensors are also known as variable-reluctance magnets or inductive sensors. These sensors don’t need any additional voltage supply. This sensor is arranged on the impulse wheel where this wheel is connected simply to the drive shaft. When the impulse wheel revolves then this sensor detects the wheel speed and results in a winding change from tooth to tooth that in turn produces a change within the magnetic flow. This sensor simply creates an AC signal through fluctuating frequencies based on the rotation speed of the wheel, after that, it is changed into a digital signal through the ABS control module.

Passive ABS
Passive ABS

How to Test an ABS Sensor with a Multimeter?

ABS sensor testing must be done whenever the ABS sensor light comes on which normally indicates a malfunctioning ABS. So, diagnosing this problem quickly is very important by using a millimeter. A technician uses a multimeter to test the sensor.

Required Tools

The required tools to test this sensor with a multimeter for properly analyzing mainly include the following.

  • A multimeter is required with an ohms setting for measuring the ABS sensor’s resistance & displays it within ohms (Ω).
  • A socket wrench is used to remove the wheel hub cover & access the sensor if required.
  • Safety goggles are used to protect your eyes whenever working below the car.
  • To keep the hands very clean, hand gloves are used while handling parts.
  • An adjustable torque wrench is used to make sure that all car bolts are properly tightened whenever reinstalling components.
  • When all of the above-required tools are collected, then it will be set to start testing your sensor. So it is very significant to keep security in mind whenever working below the car & need to follow the vehicle’s manual instructions for best results always.

Testing an ABS Sensor with a Multimeter

Testing this sensor using a multimeter is essential so that its safety & performance can be easily checked. The steps involved in testing this sensor with a multimeter are discussed below.

  • First need to disconnect the battery of the vehicle, and after that, remove the car wheel where you want to conduct the inspection.
  • Place the sensor on (or) very close to the assembly of the wheel hub.
  • A multimeter lead needs to connect to every sensor’s wire ends, after that multimeter dial needs to be set to ohm (or) resistance mode.
  • Rotate the wheels by hand & note down the readings on your multimeter; so it must read between 0.5 ohms & 4 ohms if everything is properly working. If you obtain meter readings outside of the mentioned range, then the ABS sensor needs to be replaced right away.
  • Reconnect the battery & test for proper working of ABS in a car before it is driving again.

Following the above steps will assist you in ensuring that your ABS Sensor is properly working, ensuring secure braking performance within any conditions. Ensure to verify your sensor frequently so that you can spot any problems quickly & avoid any possible accidents.

Thus, it is significant to keep in mind that the proper steps may change based on the car model, it is best always to check with user manual of your vehicle before testing the sensor using a multimeter. So, with the right maintenance & testing of this sensor, you will be able to ensure secure braking performance within all kinds of driving conditions.

Testing AC Voltage of ABS Sensor

  • Connect the multimeter’s positive lead to pin-13 & negative lead to chassis GND wire.
  • Switch on the ignition key to measure the AC voltage in between pin-13 & ground, so it must read approximately 4 to 5 volts.
  • If the voltage reading is below 4V, then there is an issue with your ABS sensor.
  • If it voltage reading is higher than 5V, then you have to correct the air gap between the sensor wheel assembly & tone ring for precise readings.

So, by following the above properly, testing an ABS sensor using a multimeter can be done easily & make sure of secure braking performance within all kinds of driving conditions. Frequent sensor maintenance & testing keeps your vehicle running safely & smoothly.

Diagnosing Sensor with an OBD Scanner Tool

To diagnose the ABS sensor, an OBD scan tool is used. This tool gives you the best solution to recognize issues that occur with your ABS sensor. So this device is connected simply to the computer of the vehicle to read any error codes that are connected to the ABS sensor. This tool can also read live information from the system to provide extra data regarding an issue. The technician must follow the instructions of the manufacturer while using an OBD scanner tool to test the sensor. So in several cases, a qualified mechanic uses both a multimeter as well an OBD scanner to ensure precise results while testing this sensor.

Why does the ABS sensor fail?

The reluctor wheel (or) tone ring easily becomes polluted (or) broken. Likewise, dust can gather on the ABS sensor which results in an erratic (or) even no signal at all. The most common causes of this sensor failure mainly include the following.

  • Internal short circuits.
  • Breaks within wiring or sensor winding because of extreme vibration
  • Improved wheel bearing clearance of the vehicle.
  • Damage in replacement of other braking components.
  • A faulty sensor impacts some significant braking functions & will show some clear warning signs like the following.
  • ABS light is the first sign normally when there is a problem through the ABS that can be caused by either a sensor (or) the control module.
  • Since the sensor provides data to the traction control system then issues could light up the traction control light too.
  • The vehicle takes a longer time to end or experiences traction loss & control whenever braking heavily.
  • The driver experiences reduced traction & wheel slippage whenever the driver drives the vehicle on wet (or) icy roads.

Advantages and Disadvantages

The advantages of the ABS sensor include the following.

  • These sensors avoid vehicle skidding by simply maintaining traction between the car wheels & the surface of the road.
  • It helps the driver maintain control of the vehicle during unexpected braking by preventing the car wheels from locking up so that the driver can steer the vehicle in any direction.
  • These sensors decrease the stopping distance of the vehicle by preventing the car wheels from locking up & allowing the driver of the vehicle to brake much harder without losing car control.
  • These sensors are very helpful in avoiding accident risks.
  • These sensors decrease wear and tear on car wheels & brakes by preventing the car wheels from locking up & decreasing the risk of skidding.
  • These sensors decrease the friction of car wheels on roads, so improve up to 30% tire efficiency.
  • Its response is much faster because of the complete electronic and also computer controller.

The disadvantages of the ABS sensor include the following.

  • The increased price of vehicles, its installation & maintenance is very expensive.
  • Longer braking distances on stable or dry surfaces can cause the vehicle brakes to vibrate or pulsate, decrease the friction between the road & wheels & increase the required distance to stop.
  • Possible failures or malfunctions of ABS can result in an erratic brake or unexpected behavior.


The applications of ABS sensors include the following.

  • These sensors are connected to all four wheels of the vehicle to prevent the vehicle wheels from locking at the braking time & develop steering control.
  • This sensor simply monitors the wheel’s speed & transmits signals to the ABS controller.
  • This sensor keeps the car braking power in check.
  • These sensors are very popular within automotive applications because of their adaptability & accuracy.
  • These sensors help in reducing stopping distances & provide you more time to maintain steering control.
  • This sensor is used in the Anti-lock Braking System of the motor vehicle.

Thus, this is an overview of an ABS sensor, working, types, advantages, disadvantages, and its applications. An ABS sensor or a wheel speed sensor is a significant part of brake control systems of cars which helps in detecting the rotating wheel speed of cars with a non-contacting measurement principle. The ABS is mainly designed to kick in throughout emergency braking conditions to assist in preventing the wheels of the car from locking up. So that it helps you maintain control over your vehicle to avoid accidents. Here is a question for you, what is air breaking system?