The anti-lock brake (ABS) system uses sensors that send data to the ABS module which will activate it during wheel lock. These sensor mechanisms are installed at the wheel, and is usually made up of two components. There will be a reluctor wheel or tone ring seated on the axle which will spin with the wheel, and either a magnetic or hall effect sensor which works together to send data to the ABS control module. Over time, the reluctor wheel may become dirty or damaged to the point where it can no longer provide a consistent reading, or the magnetic/hall effect sensor may fail. When either of these components fail, the ABS system will not function properly and will require service.
Different cars will have different ABS sensor configurations. Older vehicles may have only one or two sensors on the entire vehicle, while most new ones will have one at each wheel. Individual sensors at each wheel allow for more precise readings and operation, however, it does leave the system prone to more problems. When an ABS sensor fails, there are usually a few warning signs that will warn you that there is a problem.
1. The ABS Light comes on
The most obvious sign of a problem with the ABS system is that the ABS Light will come on. The ABS Light is the equivalent of the Check Engine Light, except only for the ABS system. When the light is illuminated, this is usually the first sign that will be displayed indicating that there may be a problem with the ABS system, and perhaps an issue with one of the system’s sensors.
2. Brakes take longer to stop car
During heavy braking conditions the ABS system should automatically activate to aid in slowing down the vehicle, and traction loss and skidding should be minimal. While we should try to practice regular driving habits that avoid heavy braking situations, if you do notice that the vehicle is taking longer to stop under heavy braking situations, or is experiencing traction loss and skidding, then that may be an indicator of there being a problem with the system. The ABS system is typically made up of only a few components - the module and the sensors - so a problem in its operation will either be with the module or the sensors.
3. Less stability under icy or wet driving conditions
Over time, most drivers will become familiar with how their vehicle handles under certain conditions, including slippery conditions, such as driving on wet or icy roads. A properly functioning ABS system will minimize any sort of traction loss, especially under wet and icy conditions. If when driving under wet or icy roads you experience any sort of tire slipping or loss of traction for more than a brief moment when stopping or taking off, then the ABS system may not be functioning correctly. This is typically due to either a problem with the module, or more likely, a problem with the sensors.
If your ABS Light comes on, or you suspect you may be having a problem with one or more of the ABS sensors, have the vehicle inspected by a professional technician, such as one from YourMechanic, to determine the exact nature of the problem, and if any repairs need to be made. They will also be able to replace your ABS Sensors if needed.
This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing ABS Speed Sensor and was authored by Eduardo Ruelas.