Auto Repair Help
LANCE’S CORNER – AUTO REPAIR HELP

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 switchBrake Warning Light 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.)

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4 Comments on "Brake Warning Light"

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maricruz barroso
4 years 7 months ago

Hi I have a question about the break warning, and what kind of brake fuil does a Ford Explorer 2003 needs

2 years 6 months ago

ABS light on. I have a 2004 Silverado 2500 HD, 92,000 mi. Dont know if fluid has ever been changed, I topped off fluid the other day it was down about 3/4″ the next day ABS light came on. No codes on the OBTII reader,removed front wheels removed and cleaned front sensors, checked voltage both were the same 1.05, unplugged all the connectors I could find for the brake system cleaned and applied dielectric grease, wasn’t sure which one was the one on the transfer case. Three days later the light went off. Could I have stirred up moisture in the brake reservoir causing the light to come on. Does the sensor detect water.

Jessica
3 months 17 days ago

I have a 2014 VW Jetta. It has been dropping temperatures to about -45C and my brake sensor went off then the air bag light and then the check engine light. I took it into a Volkswagon dealership and there was sensor malfunctions that came up in the diagnosis cheque. Then checked all my fluids and say everything is fine and reset the sensors. That was on December 27, 2017. Today on my way to work (Jan. 4/18) my break sensor went off again after driving for an hour. Could this be the moisture build up you are talking about in your article? I have scheduled an appointment for this weekend for a break fluid flush and oil change (as it is time for one) but I am worried they are just going to do it and it happen again. Could there be any other reasons for this sensor to go off (plus the additional ones that went off the first time)? Thanks for your help, I look forward to your reply.

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