Land Rover Repair: 98 Disco ABS light on, Speed Sensors Bad, deceleration rate, speed sensors

Question
My ABS light is on and the ABS "works" when it's not supposed to preventing me from being able to apply pressure to my breaks. I took my truck to an import repair shop and they said my speed sensors look bad. Are these two things related? I recently replaced a leaky master cylinder so my breaks work now, just not the ABS. What is the most common thing that goes bad with ABS? Should I buy all the ABS parts and start from scratch? Thanks, Justin

Answer
Hi Justin,

according to the LR techsheets:

For all control functions, the ABS modulator regulates the hydraulic pressure to the brakes to control the speed of all four wheels, either individually or in axle pairs.

Operation of the ABS modulator is controlled by the Self Levelling and Anti-lock Braking Systems (SLABS) ECU. The SLABS ECU also operates warning indications in the instrument pack to provide the driver with status information on each function.

The SLABS ECU continually calculates vehicle speed using the wheel speed inputs from all four ABS sensors. The calculated vehicle speed is then used as a reference against which individual wheel speeds are monitored for unacceptable acceleration or deceleration. The ABS sensor inputs are also used by the SLABS ECU to detect vehicle deceleration rate, vehicle cornering rate and rough terrain.

SO, perhaps your mechanic is referring to an ABS wheel sensor malfunction.  These are usually the main cause of ABS problems.  Second to this is the ABS modulator failing.

I hope this helps,

JohnMc