BRAKE WARNING LIGHT
by Lance Wright

The brake warning light is located in the instrument cluster area and is illuminated to warn of brake pressure loss or to indicate application of the parking brake. The brake warning light is supplied voltage from an ignition feed circuit and ground is furnished through two separate switches to illuminate the light. One switch is located in the brake combination valve or the master cylinder. In the event of a failure of one of the hydraulic circuits of the brake system, the switch will close and the light will be illuminated. The other switch is used to warn of parking brake application and is located near the parking brake lever. When the parking brake is applied, the switch is closed and illuminates the brake warning light. This circuit will usually have lower resistance than the pressure warning circuit and cause the warning light to glow brighter during parking brake application. This is done to help differentiate between causes of warning light illumination. When the brake warning light illuminates it does not necessarily indicate that you are facing a large auto repair job. But, when this light goes on, you should seek professional advice as soon as possible by visiting a reputible auto repair shop so they can troubleshoot the problem. Issues involving automobile brakes are not to be taken lightly; the ability to stop your vehicle is a very serious matter (of course).

The brake warning light (not to be confused with the ABS or anti-lock warning light) will light up when one of the following occurs:

1) Parking brake cable doesn’t completely release (or the parking brake mechanism doesn’t fully disengage)

2) Loss of brake fluid

3) Hydraulic pressure imbalance in the master cylinder

Does the light come on only in cold weather? There may be moisture buildup in the brake fluid and this moisture is actually freezing when the outside temperature falls below 32F for extended periods of time. Such freezing will cause an imbalance in the brake fluid pressure. If your car is more than five years old, has the brake fluid been flushed? If no, then the glycol-based hydraulic fluid probably has absorbed a some moisture from the atmosphere, and this moisture is freezing in cold weather.

If such moisture is indeed freezing, it may be preventing the brake system from developing equal hydraulic pressure in both halves of the master cylinder, thus creating a pressure imbalance; this will trigger the brake warning light. Get the brake system flushed and bled at your nearest auto repair shop. This will flush out all moisture in the brake system. Further, it will eliminate further corrosion of brake parts like: brake lines, calipers, master cylinders, and ABS units. If you can afford it, have your brake fluid flushed by a reputible auto repair shop every 12,000 miles.

(Lance owned his own auto repair shop for 30 years before retiring in 2006.)