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ABSolutely coincidental

Question : MY 2001 Toyota Camry has 42,000km on the clock.

After a recent regular service at an authorized Toyota workshop, the Anti-lock Braking System (ABS) warning lamp remains lit even when the vehicle is in motion.

I noticed this upon collection of the vehicle after service, and it was obviously not the case before the vehicle was sent for service.

The vehicle was returned to the same workshop for attention, and I was told that the cause was a failed wheel sensor, which needed replacement at my expense.

I am reluctant to pay for the replacement and I am seeking your advice on how the situation can be remedied.

Answer : ABS keeps your brakes from locking up on wet and slippery road surfaces, especially during hard braking in an emergency. This allows you to retain control over steering.

ABS works by monitoring the rotational speed of all four wheels during braking.

Should the speed of any one wheel be significantly slower than the others (suggesting impending lock-up), the ABS computer signals a system of valves to reduce the amount of braking pressure to that particular wheel, allowing that wheel to rotate faster.

Speed sensors are located on each wheel and transmit speed signals back to a control module that regulates the hydraulic braking pressure to each wheel.

Since the ABS is a safety critical system, the control module constantly keeps check to ensure that each and every component is functioning properly.

The failure of any one component lights the in-dash warning light and a fault code' is stored in the control module until electronically erased.

Wheel speed sensors are delicate and can easily be damaged. However, left untouched, they are usually capable of many kilometers of reliable service.

Frequently, the sensors pick up metallic particles from brake dust and these can result in a distorted signal output.

This distorted signal gets picked up by the control module and flags a fault condition for that sensor. Cleaning the sensor restores a proper signal and clears the fault condition.

However, after an unpredictable period of service, the sensors seem to fail for no reason and replacement is the only cure.

I would suspect that, in your case, the ABS sensor has failed without warning, and the timing of that failure --just after service -- could be just an unfortunate coincidence.


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