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.