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