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 how to test them.
One of the key functions of the brake light switch is to turn on and off the brake lights when the brake pedal is pressed. In addition, a bad brake light switch can trigger the ABS lights and traction control lights to stay on.
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.
List of common problems and symptoms you may experience due to a bad brake light switch:
- Brake light stays on when the car is off due to short
- Gear selector can NOT be moved out of Park into R, N, D.
- Brake lights not working.
- A car cannot be started. The brake pedal must be pressed to start the engine.
- Cruise control doesn't work
- ABS or Traction Control light comes on when driving
In most cases, the brake light switch is the culprit.
How to check the brake light switch
In modern vehicles, you can not determine if the brake light switch is defective by pressing the brake pedal and checking the brake lights. This test can be misleading.
Brake light switch has several contacts as shown in the picture below. The brakes lights may work properly but the brake light switch may still be defective and needs to be replaced.
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 diagram of the brake light switch which in some cases, maybe printed on the brake light switch itself. 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 negative side of the multimeter 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 pin. If there is no reading; that means the brake light switch is open therefore it is faulty.
If 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
Replacing a brake light switch is an easy job for most people who are handy and intermediate for people who do not really have any experience.
The brake light switch is mounted above the top part of the brake pedal, 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 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 reason; next, disconnect the brake light switch connector and remove the “c” clip. Be careful not be brake 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 the removal of 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 furthermore, 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. If the automatic transmission lever does not get out of park. The car may also not start, becasue in automatic transmission vehilces, 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 experince one of 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 deterime if the brake light switch is bad, espically 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 assembley. The short may also bee in the wire hanress. 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.