Brake System Warning Light On

Step by step repair guide on how to fix a brake warning light that has come on. This article pertains to all non-electric vehicles.

Difficulty Scale: 4 of 10

Tools and Supplies Needed

  • Wrench set
  • Appropriate brake service parts
  • Brake fluid
  • Socket set
  • Shop towels
  • Safety eye wear and clothing
Begin with the car on flat ground, in park with the emergency brake set.

Step 1 - Inspect the emergency brake lever or handle to check if its applied or if the switch is mis-adjusted or has shorted out. Replace switch or readjust as needed.

Step 2
- If the brake pads or shoes have worn down the brake fluid level in the master cylinder will be low, which will illuminate the brake warning light. Visit - Front brake pad replacement or Rear brake shoe replacement

Step 3 - When the brake system develops a brake fluid leak it can occur one of two ways, either the leak is abrupt and a massive amount of fluid has leaked out, or a slow leak will cause the fluid to leak more slowly. Either leak is not normal and immediate service is required. Using a flashlight, inspect the rear of the master cylinder, front calipers, rear calipers or wheel cylinders with front and rear brake flex hoses. There are metal fittings attached onto either end of the brake hoses, this is a common place for the hose to leak. If any brake fluid moisture is observed replacement is required.

Step 4
- Metal brake lines are used to transfer the brake fluid from the master cylinder. These lines rarely fail and when they do it is usually because of an outside force such as damage from something hitting or cutting the line. If the metal brake line has failed it is advisable to replace the whole brake line and not try to repair it.

Step 5 - Occasionally after brake system repairs have been performed, the red brake system warning light will be on. What has happened is the brake proportioning valve is offset due to a system leak. To reset this valve the car must be at a complete stop. Perform a hard pushing motion to the brake pedal and release. This action should push the proportioning valve plunger to the center of the valve, and turn off the brake warning light.

Helpful Information

The brake warning light on the dash is in red because there is an immediate danger when the car is driven. When this red light illuminates it means either the emergency brake in still set, the brake system fluid reservoir is low, or that one half of the brake system is not working (front or rear.) Brake fluid is needed to supply the necessary hydraulic pressure to activate the brake caliper or wheel cylinder. The brake system is equipped with a safety system built into the brake master cylinder by having a primary and secondary pressure chambers independent of one another. If either the front or rear section of the brake master experiences a malfunction the remaining side of the system will stop the car with impaired performance.

ABS brake systems have a yellow or orange warning light. This light is different from the red brake system warning light. When the ABS (anti-lock brake skid) system warning light comes on, it means the ABS portion of the system has stopped working. (Note: the system will still work normally, except for the ABS portion.) When this condition occurs a system scanner is needed to retrieve trouble codes. These codes will help repair the system by replacing a wheel speed sensor or main controller etc. Trouble codes will reset after a short drive once repairs have been made.

Best Practices

  • On the occurrence of a full hydraulic brake system failure the car is equipped with an emergency brake which is attached to the rear brake system.
  • Moisture in a brake system can cause the internal parts of the brake system to rust or corrode causing the seals to fail. Once this condition has occurred its recommended to replace the failed brake master cylinder, caliper or wheel cylinder with a new unit. Flush and bleed the system as needed with new brake fluid. Visit - Brake system bleed and flush
Article first published