What Your Brake Fluid Indicator Is Telling You


    – Characteristics of the brake fluid warning light

    – Brake fluid warning light: recognizing it and identifying the causes of its lighting up


The braking system is crucial to the safety of passengers and other road users. What role does the brake fluid warning light play in preventing risks due to braking? Here’s a closer look at everything you need to know about the brake fluid warning light.

The role of the brake fluid sight glass

Contrary to popular belief, its role is simply to check the level of fluid in the brake fluid reservoir, not to check the pressure and efficiency of the brake system.

Good to know: This is why its activation does not imply an emergency situation, as would an engine oil light, for example.

Of course, it is advisable to check the fluid level as soon as possible: in an extreme case of leakage, the empty jar would lead to air intrusion into the braking system with a loss of pressure and efficiency.

Note: Since different circuits supply the 4 wheels of the vehicle, it is very rare to have a total loss of braking function.

How the brake fluid indicator works

Brake fluid is stored in a jar attached to the master cylinder (brake pump controlled by the pedal). This jar, with two markings on its walls (minimum and maximum), is closed by a screwed cap. It is the one that integrates the level sensor controlling the brake fluid indicator. It includes a float which, in its lowest position, activates a contact that electrically powers the brake fluid warning light on the instrument cluster.

Identifying the brake fluid warning light

It is imperative to identify the brake fluid warning light. It is often a red or yellow pictogram representing a circle surrounded by two arcs, associated with an exclamation mark. It should not be confused with two other lights also related to the braking function:

    – The handbrake light (lit in the applied position) is identified by a similar, if not identical, symbol.

    – The indicator light of the brake pad wear also has a very similar design and is often yellow.

Good to know: for each vehicle, it is necessary to identify all these lights by consulting the maintenance booklet, which gives all the essential information.

What causes the brake fluid warning light to come on

Brake Fluid Indicator

The light only comes on when the brake fluid is low in the jar (a few millimetres below the minimum level). There are several possible causes for the light to come on:

    – A brake fluid leak. In the long term, this leak can lead to a loss of braking power and must be treated and diagnosed quickly.

    – An insufficient level of fluid but without leakage. It may be due to a maintenance fault but does not cause immediate danger to the operation.

    – A malfunction of the level sensor. Observe the liquid level in the jar through the window to check this. If it is correct, the sensor may be at fault.

Caution: As a general rule, checking engine fluid levels regularly is recommended. But when checking the brake fluid level, keep in mind that the brake system consists of components that wear out (brake pads, brake linings). As the brakes are used, the friction material decreases, the discs and drums become deeper, increasing the volume of the brake system. The brake fluid level in the jar normally drops, and it is unnecessary to top up. In fact, when the brake pads are changed, the fluid will automatically return to its maximum level.

Leave a Reply

Your email address will not be published. Required fields are marked *