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Jim Grant's Tech Tips
‘98
Oldsmobile Cutlass, Brake Warning Light
Q:
Our brake light
goes on for no reason on our '98 Oldsmobile Cutlass. Whenever, it
goes on it beeps for a while. Sometimes, the light goes on while
we are driving. It might flicker and beep. Sometimes, it beeps when
we go forward, sometimes not. Seems to be related to cold and damp
weather, but today it is warm and dry and it beeped every time we
stopped and started again.
A:
There
are two components that can cause the brake warning light to turn
on. They're the emergency brake switch and/or the brake fluid reservoir's
level sensor. More often than not the brake fluid level sensor in
the brake master cylinder reservoir is the cause of a complaint
such as yours. As the vehicle moves, the brake fluid sloshes around
in the reservoir. If the brake fluid is at the minimum level, the
movement of the brake fluid will cause the level sensor to report
low fluid level and then an okay fluid level. In addition, brake
fluid reacts to temperature as any other fluid. It expands when
heated. Therefore, when the vehicle is cold the fluid level will
be lower, not by a great amount, but lower. As you use your brakes,
they become hot. This heat is of course transferred to the brake
fluid. This results in the brake fluid to expand, causing the fluid
level in the master cylinder to rise. That would explain why the
light would be on when the vehicle is first driven (cold), and then
goes out as the vehicle is driven. With that, I'll bet a coffee
that the brake fluid level is at or below the minimum level indicator
of the brake master cylinder's reservoir. One last note, if the
brake fluid level is low, it is a good indication, that the brakes
on your vehicle may be worn and in need of service or there is a
system leak. After you reset the fluid level, oh yes and buy my
coffee, have your brakes inspected.
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