The brake warning light on my seven-year-old Mercedes-Benz C-Class came on earlier today.
I decided not to drive the car.
I later found out that it was because of low brake fluid. What is the cause?
You did the right thing by not using the car.
The brake warning light coming on means there is a problem.
Any issue with braking should be treated as critical.
The brake warning light might mean low brake fluid level in the worst case, which could be caused by a leak somewhere in the brake piping.
A small leak is not something that is obvious enough to be seen on the ground where you park.
However, even the smallest leak becomes a gushing aperture when pressure builds up every time you apply the brakes.
Within seconds, brake fluid pressure can drop to zero.
That fortunately is not something that happens often these days.
Modern braking systems use separate lines either diagonally or front and rear so that a leak in one line will not cause a catastrophic failure.
Nonetheless, brake pedal travel will increase, while braking effect will be drastically reduced.
If you have been experiencing poor braking performance and the brake warning light stays on, then you should have the car towed to a workshop.
The most common cause of low brake fluid level is worn brake pads.
When the pads thin out after prolonged use, more fluid is required in the brake callipers’ piston chambers to maintain the pads in contact with the disc.
Naturally, that will result in a drop in brake fluid level.
Once new, thicker pads are installed, the piston will be pushed back into the chamber, forcing fluid to return to the reservoir and hence restoring normal fluid level.
If the brakes work normally, the brake warning light suggests that the pads need to be replaced.
Hydraulic brake fluid does not dissipate otherwise and, as such, does not require topping up.