Reasons Why ABS Light in Your Car is On
What is Anti Lock Braking System (ABS)
Abs warning light indicates there is a problem with vehicle Anti Lock Braking system.
Anti Lock Brakes (ABS) is a safety feature which prevents brakes from locking up to avoid vehicle sliding uncontrolled when braking. ABS system was first introduced on cars in early 1970s and has become standard safety equipment on modern cars.
Anti Lock Brake system does not stop your car faster nor shorten braking distance. Actually, in most situations ABS will lengthen braking distance of a car. Anti Lock Braking primary function is to keep a car centered when brakes are applied forcibly. ABS is helpful on ice, lose ground or gravel, snow and other slippery surfaces.
ABS system will automatically “pump brakes” allowing driver to keep control of vehicle and be able to steer around obstacles.
ABS utilizes brake fluid to operate, sharing fluid and lines with braking system. A car can still be driven normally with ABS light on or with ABS system not functional. However, ABS is a safety system and should be repaired as soon as possible.
In Ontario for example ABS system is part of Vehicle Safety Certification. More on Safety Certification Ontario.
Why Your ABS Light Is On?
1- ABS Wheel Sensor
Each wheel has an abs sensor mounted on wheel hub. Abs sensors are magnetic sensors designed to monitor rotational speed of wheels and send that information ECM (computer in your car).
Based on ABS sensor information ECM will make decisions on when and which wheel to apply brakes keeping your car stable during braking, on slippery surfaces and around corners. Abs wheel sensors are the most common cause of ABS warning light.
When an ABS sensors fail, Abs system will not receive information from one or more vehicle wheels and will stop working. Warning light will be triggered and trouble codes stored.
Symptoms of Abs Sensor Failure
1. Abs light on with OBD2 codes indicating Abs sensor failure.
2. Traction control and stability control warning light triggered indication system is malfunctioning and is not available.
3. Frequent and erratic Abs activation. Abs activates when is not suppose to, even on dry pavement and very low speeds. Check OBD2 codes for more information if you feel your ABS system behave abnormally.
2- Control (ABS) Module Failure
ABS control module is an electronic module bolted into ABS hydraulic pump. ABS hydraulic pump is controlled electronically by ABS electronic control module.
Anti Lock Brake module will process information from wheel sensors and use hydraulic pump to apply or reduce brake pressure to each wheel prevention brake lock-up and skidding.
If ABS control module malfunction, ABS system will not be operative. ABS warning light will be triggered. Control module unit is usually an expensive repair.
Abs modules are generally expensive to repair with prices ranging from few hundred to few thousand dollars depending on vehicle brand and model. European made vehicles are the most expensive on parts and labor when it comes to ABS control modules replacement or repairs.
Symptoms of ABS Module Failure
1. Abs light is triggered and Obd2 codes are stored related to Abs module malfunction. Pulling OBD2 codes will pinpoint the problem on your Abs system.
2. Hard brake pedal. More power is needed to operate brakes and pedal become heavier overtime.
3. Brake Lock up. There will be no ABS activation and wheels will lock during hard braking. This can also be caused by a failed abs wheel sensor.
4. Speedometer malfunction. On certain vehicles (BMW is one of them) Abs control module control speedometer using information from one of Abs wheel sensors. If Abs control module (or sensor) fails speedometer in your car will stop working.
3- Blown fuse
A blown fuse or a relay failure will affect ABS system and will trigger a ABS warning light. Check Abs fuses is Abs system in your car is malfunctioning. Owners manual will have information on location and which fuses are related to ABS system.
4- Low brake fluid
ABS shares brake fluid with braking system. Therefore, if brake fluid leaks (from brake lines for example) pressure in breaking system will fall and trigger an ABS warning light. Leaking brake fluid can lead to brake failure and loss of braking power. Diagnose and repair brake fluid leaks as soon as possible.
While a car is still considered safe to drive with inoperative ABS system, it should be checked and repaired immediately. Safety of basic braking system is inferior to ABS equipped one and if you have brake fluid leak, it can become hazardous really fast.
More details on Antilock Braking and ESP System by Bosch.
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