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Brake Light Switch | Symptoms | Diagnostics

The brake light switch on modern vehicles is no longer a simple switch used to turn on the brake lights. A bad brake light switch, for example, can trigger the ABS and traction control lights, but it can also prevent engine start or even transmission shifting.

In this article, we go over the symptoms of a bad brake light switch and test them. 

One of the brake light switch's key functions is to turn on and off the brake lights when the brake pedal is pressed. Also, a bad brake light switch can trigger the ABS lights and traction control lights to stay on.

What does the brake switch do? 

Brake Light Switch

In modern vehicles, the brake switch signal is also used to:

  • release the automatic transmission shifter from the park,
  • allow the engine to start 
  • use the brake system to assist in emergency braking.

The brake light switch is mounted right above the brake pedal. Replacing a bad brake light switch is an easy fix. 

What are the symptoms of a bad brake light switch? 

symptoms of bad brake light switch

List of problems and symptoms that are caused by a bad brake light switch: 

  1. The brake light stays on when the car is off.
  2. Gear selector can NOT be moved out of Park into R, N, D. 
  3. Brake lights are not working. 
  4. The car cannot be started. The brake pedal must be pressed to start the engine. 
  5. Cruise control doesn't work.
  6. ABS or Traction Control light comes on when driving

One of more of these symptoms can be caused by a bad brake light. 

How to check if the brake light switch is bad? 

modern brake light switch

You can not determine if the brake light switch is defective in modern vehicles by pressing the brake pedal and checking the brake lights. This test can be misleading.

The brake light switch has several contacts, as shown in the picture below. The brake lights may work properly, but the brake light switch may still be defective and need replacement. 

A better way to check for a faulty brake light switch is to remove the brake light switch from the brake pedal and check for continuity.

You will need the brake light switch diagram, which may be printed on the brake light switch itself in some cases. On most brake light switches, there are two, four, or up to six pins.

Use a multimeter and set it to ohms. Probe one of the pins with the multimeter's negative side and the positive side of the multimeter touching each of the pins on the brake light switch.

There should be a continuity reading of zero on at least one of the pins. If there is no reading, that means the brake light switch is open; therefore, it is faulty. 

Suppose the brake lights work properly; test for brake light switch power. Locate the wire connector that plugs on the brake light switch. Use a voltmeter and probe the power source area. 

The brake pedal stopper can also contribute to a brake light staying on. There is a brake light stopper where the brake light switch comes in contact with when the pedal is not pressed.

Over time, this stopper wears out, or it can also come out of place. When this happens, the brake light will stay illuminated at all times.

This problem can often be fixed by adjusting the position of the brake light switch. Most brake light switches will allow you to adjust them slightly to accommodate normal wear.

When you adjust the brake light switch, make sure it is pressed against the brake light stopper. If the stopper is missing, replace the stopper before condemning a faulty brake light switch. 

How to replace a brake light switch yourself? 

location of brake light switch

Replacing a brake light switch is an easy job for most handy and intermediate people for people who do not really have any experience. 

The brake light switch is mounted above the brake pedal's top part, close to the pivot area. Battery power is fed to the brake light switch from the ignition switch or the Engine Control Unit (ECU). When the brake pedal is pressed, it closes the switch, and the current flows through the wiring to the brake lights.

This turns on the rear brake lights. The brake light switch can also be located on the master cylinder.

Hydraulic pressure from the master cylinder brake light switch system can close the switch to turn on the brake lights.

For example, on a Honda brake light switch, the brake light switch is held in place by a nut. First, start by disconnecting the connector.

Next, remove the nut and turn the brake light switch counterclockwise. And turn the brake light switch counterclockwise. This should remove the brake light switch.

On GMC vehicles, the brake light switch is normally held in by a “c” clip. Disconnect the battery for safety reasons; next, disconnect the brake light switch connector and remove the “c” clip. Be careful not be break the “c” clip.   

If you replaced the brake light switch and you are still experiencing problems, here is what you should check.

  • Adjust Brake Light Switch (if there is room.)
  • Brake Light Fuse
  • Brake Light Stopper / Bumper Pad
  • Brake Light Wire Harness

How much does it cost to replace the brake light switch? 

Normally, the brake light switch does not cost much. Usually ranging from $30-$100 for most vehicles, and the labor usually ranges from $50-$300 depending on the shop rate, flat rate, and difficulty of the job.

The job itself usually takes anywhere from 10 minutes to 2 hours to replace on most vehicles.

However, on some vehicles, the brake light switch can be placed in an inconvenient location requiring removing several components. This will increase the cost of the job.  Be sure to replace the brake switch as soon as possible. 

Note that a bad brake light switch can potentially drain your battery if the light stays on, and it can also decrease your rear brake light lifespan. 

Frequently Asked Questions

How do you know if the brake light switch is bad?

Brake light switch may be bad if your brake lights don't work. Suppose the automatic transmission lever does not get out of the park. The car may also not start because, in automatic transmission vehicles, the car needs to detect that the brake pedal is pressed. If the brake light switch is bad, the Engine Control Unit (ECU) will think you are not pressing the brake pedal, therefore not allowing you to start the car. All cars have manual Park release for the automatic transmission. You may experience one or more of these symptoms if the brake light switch is bad. Pressing the brake pedal and looking if the brake lights turn on and off is not a good test to determine if the brake light switch is bad, especially on newer vehicles. 

I replaced the brake light switch, but my lights keep burning out or stay on.

This problem is often caused by a short in the tail light assembly. The short may also be in the wire harness. Shorts can develop inside the tail light, or the wire harness has a short where the trunk hinges to the car. Another possibility is the brake light housing (typically negative) shorting to any metal parts in the trunk.