If the Brake Warning Light is on all the time, it could mean you simply forgot to release the parking (emergency) brake. The brake warning light remains on when the brake is set as a reminder. If the brake warning light remains on when the parking brake is released, then something else is wrong.
In some cases, the brake warning light may remain on if the switch on the parking brake pedal or lever is misadjusted. A simple adjustment should fix the problem.
If the brake warning light comes on when you start your car, while driving or when you step on the brake pedal, it means that hydraulic pressure has been lost in one side of the brake system or that the fluid level in the master cylinder is dangerously low. The cause is usually a fluid leak somewhere in the brake system.
In any event, check the fluid level in the master cylinder. If low, add brake fluid to the master cylinder reservoir to see if this causes the warning light to go out. This may temporarily solve the problem, but if your brake system has a leak, the new fluid will soon be lost and the warning light will come back on.
Brake fluid leaks are DANGEROUS because they may cause your brakes to fail! Because of this, your vehicle may be unsafe to drive.
If the brake pedal feels soft, unusually low or goes all the way to the floor when you step on it, DO NOT DRIVE your vehicle! Have it towed to a service facility so a competent mechanic can inspect the brakes and make the necessary repairs.
The entire brake system should be inspected to determine why the warning light is on. Leaks can occur in brake hoses, brake lines, disc brake calipers, drum brake wheel cylinders or the master cylinder itself. Wet spots at hose or line connections would indicate a leak that needs to be fixed.
Leaking brake fluid can also contaminate the brake linings, causing them to slip or grab. The uneven braking action that results may cause the vehicle to veer to one side when the brakes are applied. Brake shoes or pads that have been contaminated with brake fluid cannot be dried out and must be replaced.
Vehicles that are equipped with Anti-Lock Brakes (ABS) have a special warning light just for the ABS system. The ABS lamp should come on when the ignition is turned on for a bulb check, then goes out after the engine starts. If the ABS warning light remains on or comes on while driving, it indicates a fault has occurred in the ABS system.
On most applications, the ABS system disables itself if the ABS warning light comes on and remains on. This should have no effect on normal braking. However, the safety benefits of ABS will NOT be available in an emergency situation or when braking on a wet or slick surface if the light is on and system is disabled.
CAUTION: If the Brake Warning Light also comes on and remains on while the ABS warning light is on, it usually means the system has a fluid leak and that your vehicle is UNSAFE to drive. The entire brake system and ABS system need to be inspected to diagnose what is wrong.
If the ABS light comes on momentarily then goes out, the nature of the problem is usually minor and the ABS system usually remains fully operational. It might be a momentary sensor fault.
A scan tool can be plugged into your vehicle's diagnostic connector to read any ABS related fault codes and other system information. Typical problems that can set codes and turn on the ABS Waring Light include Wheel Speed Sensor faults (bad sensor or bad wiring), problems with the ABS pump or high pressure accumulator, or control module faults.
When you step on the brake pedal, the brake calipers squeeze the disc brake pads against the rotors to create friction that slows your vehicle. If your vehicle has drum brakes in the rear, the rear brakes push the shoes outward against the drums to create friction and slow your vehicle. In both cases, there is always a potential for some light noise.
Damp weather can make some brakes absorb moisture, which creates some light squealing when the brakes are cold, or when backing up. Once the brakes are applied and warm up, the noise goes away. This is normal and is not a problem.
Certain types of brake linings such as semi-metallic pads are harder and contain a lot of metal fibers in the friction material. Because of this, they tend to be noisier than other friction materials such as ceramic and nonasbestos organic brake pads. Again, this is normal and does not affect the stopping ability of your vehicle.
If you find brake noise annoying, you can replace the original equipment brake pads with aftermarket premium quality ceramic brake pads that are typically much quieter.
As brake pads wear, they become thinner and thinner until the friction material is almost gone. Some pads have a small metal tang that is designed to scrape against the brake rotor when pad wear reaches minimum thickness. The wear indicator make a light metallic scraping noise, signaling you it is time to replace the brake pads. The brakes should be inspected to see if this is the cause, and if so the old worn out pads should be replaced with new ones.
If brake pads wear all the way down until the friction material is completely gone, the steel backing plates on the pads will drag against the rotors when you step on the brakes. This will produce a LOUD metallic scraping noise. You'll also notice that it takes a lot more pedal effort to brake and that the stopping distance takes much longer. Brakes in this condition are VERY DANGEROUS. You should NOT drive your car until the brakes have been repaired.
Brakes are a wear component. How long they last depends on a lot of variables, so that's why most new car warranties do not cover brake pads. Larger heavier vehicles tend to wear out their brakes much faster than smaller lighter cars. City driving with lots of stop-and-go traffic also wears down brake pads much faster than highway driving. Aggressive driving and heavy braking also increases the rate at which the pads wear out.
The type of friction material used in the original equipment brake pads also affects their lifespan. Harder semi-metallic friction materials and certain ceramic pads typically outlast softer nonasbestos organic friction linings.
Because of these things, brake wear can vary quite a bit from one vehicle to another, and from one driver to another. If most of your driving is around town in heavy traffic, it's not unusual to need new brakes after 30,000 to 40,000 miles of urban driving. On the other hand, if most of your driving is on the open highway, your original equipment brakes might last upwards of 60,000 to 70,000 miles or more.
The front brakes typically wear at up to twice the rate of the rear brakes on most vehicles, although on some FWD cars the front and rear brakes wear at almost the same rate.
The only way to know if your brakes are worn out and need to be replaced is to measure the thickness of the friction linings on the pads. Minimum thickness specifications will vary depending on the application, but as a general rule is about 1/8th inch (2 to 3 mm).
Brake pads should also be replaced if the friction material has been contaminated with brake fluid from a leaky brake caliper or hose, or if the friction material is cracked, flaking or loose on the pad.
Uneven pad wear, tapered pad wear or a difference in the thickness of the inner and outer pads may also be reasons for replacing the pads (as well as the calipers).
New brake pads should be the same or better friction material as the original. Premium quality replacement brake pads are recommended for best braking performance and longevity.Ceramic pads are generally quieter than semi-metallic pads. Follow the replacement recommendations of the brake supplier.
On a vehicle with relatively low miles (under 50,000) and no brake problems other than worn pads, all that may be needed is a simple pad replacement. The cost should be no more than $150 to $200 depending on the cost of the pads and the hourly labor rate of the shop that is doing the work.
If your vehicle also needs new rotors because the original rotors are worn or damaged, that will add another $100 or so to the price.
Flushing out the old brake fluid and refilling and bleeding the hydraulic lines may add another $50 or so to the bill.
If the calipers or other brake hardware needs to be replaced because of leaks, corrosion or wear, the cost will increase depending on the parts. Add several hundred more dollars to your bill.
Brake repairs can get VERY expensive if repairs have to be made to the ABS modulator, pump, accumulator and/or control module. This can add up to several thousand dollars to the cost depending on the year, make and model of your vehicle! ABS components on import luxury brands can be very pricey and difficult to source.
The important point here is that ALL brake system components that are worn out, damaged, badly corroded or defective need to be replaced to restore the safe operation of your vehicle. The brake system is not a place to cut corners to save money.
On the other hand, if a shop is trying to sell you a lot of parts your vehicle many not actually need, find another shop to do the work or learn how to do your own brake job.