What is a Brake Interlock System?

A brake interlock system (also known as a shift interlock solenoid) is a safety function installed in modern vehicles that ensures the car can’t be shifted from park if the brake pedal is not engaged. This system works together with the neutral safety switch and the brake light switch. 

Many vehicles don’t have the interlock installed, despite the relatively affordable cost for labor and installation. 

There are many kinds of interlocks such as a brake shift interlock, a starter ignition interlock, and a brake transmission interlock. In certain types of vehicles (minivans, for example), the brake shift interlock device is in a different location than the other car components. 

What Are Brake Interlock Systems For?

These systems were installed in many vehicles to keep the car from inadvertently shifting into drive or reverse by a vehicle occupant who didn’t know what they were doing. A typical example of this is if a child climbs in the front seat while the family stops in a parking lot and the child accidentally shifts a car into gear. 

Car accidents have occurred when vehicles roll down the road in reverse, even though the driver might have previously put the car into park. This issue is caused if the safety feature were to fail. When working correctly, the brake shift interlock system ensures that the vehicle cannot be shifted from the park position unless the brake pedal is pressed. 

Brake shift interlock failure can also take place if the stop lamp bulb shorts out or if there are issues with a trailer plug. Before operating your vehicle, be sure stop lamps are working correctly. 

How to Know If a Shift Interlock Is No Longer Functioning Correctly

The shift interlock solenoid can become worn out over time. If you believe this component could be failing, be aware of these warning signs

Problem #1: Car Won’t Shift from the Park Position

If this issue is preventing you from driving your car, you can try seeing if the button for the shifter release is not pressed. Also, check to see if the shifter can still move. If so, the shifter interlock solenoid could be worn out, and you might need a replacement shift interlock solenoid, so it’s best to contact a certified mechanic. 

Problem #2: Dead Battery

If the car doesn’t let you shift it from park at all, it might be due to a dead battery. Are any of the electrical parts or lights working? If so, the problem might lie in the battery instead of the brake interlock system, which is much simpler to correct. For this issue, you might only have to jump the battery, and a mechanic can help with this. If the battery gets jumped and the car or truck still won’t shift into drive, then the problem could be the shift interlock solenoid.

In summary, the brake interlock system (also known as the shift interlock solenoid) are critical safety components of modern vehicles. These devices ensure the car or truck can’t be shifted from the park position unless the vehicle is turned on and the brake pedal is not engaged. If the car won’t shift from park, it’s possible that the brake interlock system needs replacement.