If your brake warning light is illuminated red, stop immediately and investigate the cause.
So, what could a brake system warning light mean? Brake warning lights come in two basic colours, amber and red. The amber colour lets you know you have an issue but it’s not an emergency. The red warning light tells you this is an emergency. Common brake warning lights include:
- Park brake warning light
- Brake system warning light
- ABS fault warning light
By the end of this guide, you’ll understand what the different warning lights mean and what you need to do to fix it your problem.
Park Brake Warning Light
The park brake warning light, as its name suggests lets you know the parking brake (emergency brake) is on. This light remains on as long as the park brake is applied, with even one click.
The warning lights sole purpose is to alert the driver to the park brake status. While driving with the park brake partially on isn’t as serious as having no brakes, it does illuminate a red warning light on your dash.
Other possible reasons for the park brake warning light staying on include:
- Brake assembly not making contact with the sensor, a simple adjustment will fix this problem.
- Wiring fault – Most park brake dash warning lights are activated by a simple grounding of the sensor as the parking brake is activated. If the wiring grounds at a pinch point in the harness, the warning light will activate. A continuity check of the grounding wire will indicate a short to ground.
Brake System Warning Light
The brake system warning fault light is coloured red for good reason, it means you have a brake problem that needs immediate attention.
In some older less sophisticated models this warning light also warns the driver that the parking brake is on.
In many cases, this warning light comes on because the system has detected a low brake fluid level in the reservoir. That’s easy to check. The reservoir is the clear-coloured container attached to the brake booster at the bulkhead. It has a max/full and min/low indicator. The warning light comes on if the fluid is below or close to the low mark.
Worn brake pads
Having a low brake fluid level is commonly caused by worn brake pads or shoes and is quite normal. The more the linings wear, the lower the fluid gets. Sometimes you may notice the light only comes on when the vehicle turns a bend sharply.
Most cars employ a simple grounding wire embedded in the brake pad material. As the brake pad wears the sensor grounds and illuminates the brake warning dash light. You may also notice increased brake noise when operating the brake pedal.
No need to top up the fluid as it’s likely OK, instead inspect and replace the pads/shoes and check the fluid level afterwards.
The other possibility is a leak, brake systems commonly leak from corroded brake lines, cracked or perished flexi hoses, rear brake cylinder seals and caliper seals. A brake fluid leak should be obvious, the brake pedal will feel spongy and an oily patch on your driveway or on the inside of the wheel is a good indicator.
If you have a leak, your car is not safe to drive, topping up the reservoir won’t restore braking force, the system will need to be repaired by a professional.
Most modern cars and some high-end older cars will have a differential pressure sensor. For safety reasons, the master cylinder has two independent chambers that apply equal force.
Each of these chambers is dedicated to braking two wheels, some vehicles couple the wheels diagonally and some front and back.
If one brake circuit develops a leak and losses pressure, the other circuit is unaffected and is capable of stopping the vehicle safely.
The pressure sensor will set the warning light if it senses a pressure difference. Some cars will illuminate the warning light only as you apply the brakes.
A faulty sensor or wiring can also set the warning light.
ABS Fault Warning Light
The anti-lock braking system is designed so as not to effect the braking capability of a car in the event of ABS failure. In many cases, most cars will travel hundreds if not thousands of miles without ever activating the ABS system.
ABS is particularly useful in emergency braking where the wheel sensors help prevent lockup which allows the vehicle to steer around obstacles.
The system will require a scan tool to interrogate the ABS control module. Some causes are obvious like damaged wiring or disconnected sensors, so it’s always worth inspecting the system.
A basic ABS system includes:
- Brake pedal switch
- Wheel speed sensors
- Hub sensor rings
- ABS control module
- ABS modulator
Early evolutions of the ABS system were more complicated, they were designed as one braking system, unlike more modern systems which run in parallel.
Common faults with ABS systems include:
- Faulty wheel speed sensor
- Disconnected wheel speed sensor wiring
- Corroded wheel speed sensor connectors
- Faulty brake force sensor
- Faulty brake light switch/bulbs
- Faulty control module
- Faulty ABS pump
- ABS warning message
Can A Bad Wheel Bearing Cause ABS Light To Come On?
ABS wheel speed sensors (WSS) send the speed of each wheel to the ABS control module. The module processes the information and makes activation decisions based on the speed difference of each wheel.
For the sensor to work it needs a sensor ring. The ring is positioned in the wheel bearing or on the drive shaft, it moves with the wheel.
The sensor itself is positioned in the hub or knuckle at a very precise distance from the sensor ring. Any variation in the air gap will cause a error in the signal which the ABS control module will recognise as a fault and illuminate the ABS warning light.
A worn wheel-bearing with free-play will cause the ABS light to come on, in addition if the sensor ring makes contact with the sensor it may damage it. The sensors can’t be repaired.
Another common cause of wheel speed sensor faults is corrosion. A build up behind the sensor causes the air gap to change which as you know sets the ABS warning light.
Why Is My ABS Light On After Changing Wheel Bearing?
Changing a wheel bearing on most cars involves pressing out the old bearing and pressing in the new one. It’s easy to damage a wheel speed sensor, sensor ring on the bearing or on the drive shaft.
Some cars as you know have the sensor ring in the wheel bearing, it is possible to fit the bearing back-ways, meaning the sensor ring is facing the wrong way.
The sensor must fit in the hub/knuckle snugly, if the air gap is wrong, the ABS light will come on.
It’s possible that the wrong wheel bearing is fitted, while mechanically it’s a good fit, the sensor ring may not be compatible with your ABS control module.
If you need brake system tools, check out the “Brake repair tools page”
You may find the brake resources page useful, it’s a fluff-free guide to DIY brake repairs.
Can I Drive With ABS And Brake Light On?
It’s not safe to drive a vehicle with a red brake system warning light and an ABS light on. In most cases, it’s OK to drive with just the amber ABS light on.
Check your brake fluid level, the fluid should be above the low-level mark on the reservoir. If it’s below this level check under the car for obvious signs of a fluid leak. If you don’t see any signs of a leak, top up the fluid using only the DOT recommended on your brake fluid reservoir cap.
Try to avoid mixing fluid types, they all have a different boiling point, however, it won’t hurt the system if you do.
But don’t mix DOT 5 fluid with any of the others, DOT 5 is special, it’s silicone based and only use it if it’s marked on your brake fluid reservoir cap.
If your brake pedal feels soft, call a tow truck, as the vehicle is not safe to use.
What does it mean when your ABS and brake light comes on? When both warning lights come on, it usually indicates that there is a major problem with the main braking system and as a result, the ABS system has been disabled.
How do I get my ABS light to go off? Often ABS warning lights come on because of a very minor issue, try restarting the car and driving above twenty miles per hour to reset. If the light fails to go out, you’ll need a scan tool to diagnose stored and live trouble codes.
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.