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Your Abs sensor worn out? » Read more about common malfunctions • Repair • Replacement manual
Permanent steering with the ABS sensor
The ABS sensor is a small, yet important part in the braking system of modern cars. It is part of the ABS system, ensuring that a car remains steerable in case of an emergency stop.
History of the ABS
Even though the ABS has a modern ring implying an exclusive accessory its origin goes back to the year 1902, when the first attempts in this area were made on steam trains. It became really important when airplanes had to be able to land at high speed. Planes often became unstable when braking on the tarmac, pulling to one side. The problem with blocking wheels is that a vehicle can no longer be steered. The ABS or anti-lock braking system was a great solution in this area. The first ABS installation in a car was in the British sports car JENSEN FF. The German car industry installed the first ABS in the 1978 Mercedes S-class, soon followed by the BMW 7-series. From there on, ABS quickly spread to the standard equipment of compact cars.
Construction and location of the ABS sensor
The ABS consists of an engine speed sensor, ABS ring and a control unit. In the technical sense an ABS sensor is quite simple: it is only a magnet sensor, emitting a signal when it approaches a magnetic field. The ABS ring causes this: this iron toothed (or perforated) ring permanently registers the magnetic field that successively appears and disappears from tooth to tooth or perforation to perforation during normal driving. This frequency is transmitted to the control unit. As long as the ring registers a permanent motion of the wheel, the ABS leaves the brake alone. When during braking the wheel blocks, the control unit unblocks the brake in impulses resulting in the so-called "stutter brake". This enables the driver to keep the car under control and avoid an obstacle when suddenly braking.
Defects and repair of the ABS sensor
When the ABS sensor is defective, it is immediately perceived. The control unit no longer receives signals and assumes that wheel is blocked. With every braking manoeuvre the control unit causes the stutter brake, making driving with a defective ABS very uncomfortable and unsafe. An ABS sensor can be damaged internally, the cables can have become detached or the contacts are corroded. The sensor sits close to the road and is therefore exposed to the weather and splashing water. A malfunctioning sensor causes a warning lamp to light on the dashboard. This function is sufficiently sensitive for the lamp to light up before the sensor function totally fails. Replacing the ABS sensor is very simple. The wheel is removed, the old sensor unscrewed and replaced by a new one. The distance between sensor and ABS ring must be aligned again with a feeler gauge. After connecting the control unit, the system should function again. Sometimes the unit has to be programmed into the new ABS sensor. This is a job for garages. Replacing the ABS sensor automatically involves checking the entire brake system: this is an excellent occasion for a visual check of brake linings with wear sensors, brake discs, brake lines and hoses.
Costs for ABS sensors
The times when electronic components cost a fortune, are long past. Prices for a brand quality ABS sensor start at 7 EUR (c. £6) per piece. At these low prices it is recommended to replace the components before the end of their life span as a precaution. Principally, ABS sensors are not built as typical wear parts. Under ideal circumstances they should last as long as the car: 15 years and 250.000 kilometres. Nevertheless its vulnerable position is not optimal for such a long use. We recommend therefore replacing preventively the ABS sensor every 100.000 km. This makes the car permanently safe, brake-ready and steerable.