Question: My brake warning light is on. What does it mean?
Answer:If the light is on all the time, it could mean
you simply forgot to release the parking (emergency) brake. The
brake warning light remains on when the brake is set as a reminder.
If the brake warning light remains on when the parking brake is
released, then something is amiss.
In some cases, the brake warning light may remain on if the switch
on the parking brake pedal or lever is misadjusted. Nothing is
wrong with the brakes and a simple adjustment should fix the problem.
If the brake warning light comes on when you apply the brakes,
or is on continuously, it means that hydraulic pressure has been
lost in one side of the brake system or that the fluid level in
the master cylinder is dangerously low (due to a leak somewhere
in the brake system). In either case, the fluid level in the master
cylinder should be checked. Adding brake fluid to the master cylinder
reservoir may temporarily solve the problem. But if there's a
leak, the new fluid will soon be lost and the warning light will
come back on.
Brake fluid leaks are serious because they may cause the brakes
to fail! So avoid driving the vehicle until the system can be
inspected to determine what's wrong. Leaks can occur in brake
hoses, brake lines, disc brake calipers, drum brake wheel cylinders
or the master cylinder itself. Wet spots at hose or line connections
would indicate a leak that needs to be fixed.
Leaking brake fluid can also contaminate the brake linings, causing
them to slip or grab. The uneven braking action that results may
cause the vehicle to veer to one side when the brakes are applied.
Brake shoes or pads that have been contaminated with brake fluid
cannot be dried out and must be replaced.
BRAKE WARNING LIGHT CIRCUIT
The brake system is divided into two hydraulic circuits. On most
rear-wheel drive vehicles, it is divided so one circuit applies
the front brakes and the other applies the rear brakes. On front-wheel
drive cars and minivans, the system is usually split diagonally.
One circuit works the right front and left rear brake, and the
other works the left front and right rear brake. This is done
for safety purposes so if one circuit loses all its brake fluid
and fails, the vehicle will still have one remaining circuit to
apply two wheel brakes.
Usually located on the master cylinder or the brake lines exiting
the master cylinder is a "pressure differential" switch.
If either brake circuit develops a leak and loses its fluid, the
difference in pressure when the brakes are applied will trip the
differential switch causing the brake warning light to come on.
ABS WARNING LIGHT
On vehicles equipped with antilock brakes (ABS), a second warning
light is provided to warn if a problem occurs within the ABS system.
The ABS lamp comes on when the ignition is turned on for a bulb
check, then goes out after the engine starts. If the ABS warning
light remains on or comes on while driving, it indicates a fault
has occurred in the ABS system.
What happens next depends on the nature of the fault. On most
applications, the ABS system disables itself if the ABS warning
light comes on and remains on. This should have no effect on normal
braking. Even so, ABS will NOT be available in an emergency situation
or when braking on a wet or slick surface.
CAUTION: If the brake warning light also comes on and remains
on while the ABS warning light it on, it signals a serious problem.
Your vehicle may not be safe to drive. The brakes and ABS system
should be inspected immediately to determine the nature of the
problem!
If the ABS light comes on momentarily then goes out, the nature
of the problem is usually minor and the ABS system usually remains
fully operational. Some vehicle manufacturers call this kind of
fault a "nonlatching" fault (meaning it isn't serious
enough to disable the ABS system).
Regardless of the type of fault that occurred to trigger the ABS
warning lamp, a special "code" is recorded in the ABS
module's memory to aid in diagnosing the problem. On some vehicles
this code can be retrieved by putting the ABS system into a special
diagnostic mode. The code is then flashed out through the ABS
warning lamp. The code number refers to a diagnostic chart in
a service manual that must be followed to pinpoint the faulty
component. On other applications, a special "scan tool"
must be plugged into the vehicle's diagnostic connector to read
out the fault code.
Diagnosing ABS problems requires a fair amount of knowledge and
expertise (as well as special equipment in many applications),
so this job is best left to a competent professional.
