It is both frustrating and unsafe to drive your GMC Terrain if the brake lights are stuck on. The most common reason that they stay on is a brake light switch that has failed.
How Brake Lights Work
Brake lights work by having an electric current sent to the brake pedal switch at all times (even with the vehicle off). When you press the brake pedal in, it sends the current to the brake lights. It’s a very simple system that has not changed in almost a century.
Brake Lights Stuck on Causes: GMC Terrain
Here are some of the most common reasons why your GMC Terrain’s brake lights may be stuck on. Most of them are related to the switch that turns them on or off. They are written in order from most likely to least likely to be causing the problem.
1. Bad Brake Light Switch
Underneath the dashboard there is a switch that the brake pedal presses into. When you press the brakes this switch is activated and the brake lights turn on. When you take your foot off the brake, it presses this switch in and the brake lights turn off.
The inside of the brake light switch can wear out from the hundreds of thousands of times you press your Terrain’s brakes. When this happens the brakes can stay on. Replacing the brake light switch is far and away the number one thing that fixes brakes that are stuck on. They are not very expensive, and they are easy to do yourself.
See Also: GMC Terrain Brake Pedal Going to Floor
2. Brake Switch Adjustment
Nearly all brake switches have an adjustment built into them that allows them to to snug up to the pedal. If this adjustment is off, the plunger on the brake pedal switch will not press in all of the way. This keeps the brake lights perpetually on.
3. Weak Brake Pedal
If the brake pedal is closer to the floor than it should be, the plunger in the brake pedal switch will no longer be able to be pressed in all the way. This keeps the brakes lights on even when the switch is just fine.
To test whether or not this is the case, put your feet behind your Terrain’s brake pedal and pull it up. Did it turn the brake lights off? If it moved a lot higher it’s a sign that the pedal is softer than it needs to be. If it barely moved at all, but the brake lights did turn off, it probably still means that you need a new brake pedal switch. Or it could be just ever so slightly out of adjustment.
4. Wiring Issue
It is possible that a wiring harness issue has caused some of the wiring to melt together, or short out in some way. I’ve personally seen this, but it is a 1% of the time or less issue.
The easiest way to diagnose brake lights that are stuck on is to unplug the wiring harness to the brake pedal switch. If the brake lights turn off, you know that the switch is bad. If the brake lights stay on, you’ll need to find the wiring problem.
Conclusion: Terrain Brake Lights Stuck On
Good luck diagnosing why your Terrain’s brake lights aren’t turning off. If there is anything that you might be able to add for the next person, your comment would be appreciated. Good luck!