Your ABS system performs a self-test every time you start up the car, and if its
computer detects an issue with one of its sensors or hydraulic pumps, a light on your
dashboard may illuminate alerting you of such problems.
As soon as this warning appears, it could signal a serious issue with your vehicle.
Check brake fluid
Your 2007 Prius ABS system monitors how hard you press on the brake pedal and
responds accordingly, to prevent brake pads from wearing down too quickly and
enable higher speeds of driving. It features various sensors connected with its
controller; when one fails, its light may illuminate and cause difficulty stopping or
slowing down your car.
As a first step, try switching off and on again the engine – this acts like rebooting a
computer and may help clear any temporary glitches which have confused the ABS
controller.
If this fails, unplug the main wiring harness and inspect its connectors at each end
for signs of corrosion; signals traveling down these wires are only millivolts so any
resistance in their contacts could impede signal flow. Also make sure that wheel
speed sensors are operating as they should.
Check brake lines
ABS sensors notify a computer (known as a controller) whenever one or more wheels
stops rotating while moving, prompting it to release brake fluid pressure by
signaling hydraulic valves to release brake fluid pressure on another wheel and
rotate it again – a process repeated several times every second; in cases where
insufficient data are received by controller, your ABS warning light may illuminate.
If the light remains illuminated, it’s time to visit a shop equipped with a code reader
capable of communicating with your ABS controller. A technician will plug this reader
into your ABS controller and attempt to access its memory for trouble codes stored
there.
If the code doesn’t appear, then most likely there’s something wrong with either
your master cylinder measuring brake fluid or parking brake sensors. An
experienced in brake repair should be able to assess and replace them quickly and
accurately.
Check brake calipers
If you want to keep things as straightforward as possible, blocking the brake
bleeders so that no new brake fluid is lost during removal is an effective strategy;
however, as per Toyota TSB BR0012, this approach should not be undertaken.
The ABS system relays feedback from pedal position sensors to its control module
and then interprets it to determine how much pressure should be applied,
staggering each wheel’s braking to protect tires and maintain traction during
braking. Unfortunately, its control module can become dysfunctional and set the
ABS light or trouble codes; typically these issues can be repaired with special service
tools (SST) and bridge wires; in extreme cases it may require replacing it entirely –
taking these steps will help avoid costly repairs or accidents altogether. Take your
safety seriously: if your ABS light illuminates, DO NOT DRIVE YOUR CAR!
Check brake pads
If both ABS and brake warning lights light up together, this indicates an extremely
serious problem with your car’s ABS system, parking brake or wheel speed sensors –
do not drive until a certified technician inspects it first. These lights illuminate when
either its module, parking brake or speed sensors have malfunctioned.
Sensor issues usually stem from dirt, corrosion or physical damage to tone rings or
sensors themselves. One or more wheels may also lose traction due to worn or
damaged tires or hitting an object such as rocks, potholes or pots of dirt in its path.
If the brake fluid seems adequate and unplugging and reinserting the main harness
has failed to resolve your issues, it may be worth investigating the ABS controller. As
this unit contains complex hydraulics and electronics without user serviceable parts,
replacement will likely be costly.