Damaged brake light switchA faulty brake light switch is one of the most common reasons that your gear shifter may be stuck in park. The brake light switch performs a few functions. The main job of the switch is to turn your car's brake lights on when you depress the brake pedal. However, the switch does much more than that, and it's also a safety mechanism that plays a key role in various other systems. In vehicles with automatic transmissions, drivers must press the brake pedal to shift out of or into park. If the sensor fails, it will be unable to send a signal to the shift interlock solenoid, meaning you won't be able to move your shifter out of park, even if you're pressing the brake pedal.A faulty or malfunctioning brake light switch is a common cause of a shifter that you can't move out of park, but the same issue can be caused by a blown brake light fuse. Either way, the fix is relatively simple: replace the worn-out or broken part. A brake light switch replacement should cost around $100, depending on your vehicle and the labor rates in your area. A fuse replacement will likely cost less than $50. Both fixes are relatively simple and straightforward, and you can DIY them if you want to save some cash. A fuse replacement will be significantly easier and only requires you to replace the old fuse by accessing the fuse box under the hood or inside your car's cabin. A brake light switch replacement is also pretty simple, and, in most cases, only involves replacing the switch located under the dash near the brake pedal.Faulty shift interlock solenoidOutside of a damaged brake light switch, a faulty or malfunctioning shift interlock solenoid is another one of the most common causes of a shifter stuck in park. The shift interlock solenoid works with the transmission control module (TCM) and is responsible for ensuring that your car stays in park unless the brake pedal is depressed. If the solenoid fails, the TCM will be unable to disengage the park gear, resulting in an inability to shift into a driving gear. The solenoid is typically located underneath the center console in vehicles with a center console shifter, and beneath the steering column in vehicles with column shifters.If the solenoid fails, you'll need to replace it. However, it's worth noting that the solenoid can fail due to electrical issues like an open circuit. Your mechanic should test for electrical problems before replacing the solenoid. But if you want to do it yourself, you'll need to check the solenoid with a multimeter or test light while the ignition is ON and the brake pedal is depressed. If the solenoid is receiving power, then there's a deeper electrical issue which you or a professional will need to identify — replacing the solenoid alone will not fix the problem in this case. That said, a shift interlock solenoid is a fairly inexpensive replacement. If you pay a mechanic to do the work for you, you should expect the cost to fall somewhere between $150 and $250, depending on your car and local labor rates. Performing the job yourself will save you some cash, as you'll only need to buy the new solenoid, which should cost between $50 and $100.Damaged shift mechanismIn the past few years, some automakers have begun building vehicles with automatic transmissions that use electronic gear shifters, meaning they rely on buttons and electric interfaces to actuate gears inside the transmission. In contrast, the vehicles built in previous decades and a large number of the cars on the road today — including many modern vehicles — have mechanical shift mechanisms. Cars with mechanical shifters rely on a lever or shift knob and a cable to physically move your transmission between gears like park, reverse, and drive. Over time, the cable and accompanying components can develop damage, stretch, or break entirely. If this occurs, you may be unable to shift out of park, or into any other gear.Like many of the other issues described here, this problem requires replacing the broken or damaged part. If you visit a professional mechanic to have your shift cable replaced, you'll likely pay around $350, depending on your car's make and model and the shop's labor rates. Performing the service yourself allows you to save on labor fees. However, the job is more complex than many of the other fixes on this list. The job requires removing the center console or steering column to access the cable, disconnecting the cable from the transmission, and routing a new cable between the two locations. It is possible to DIY your shift cable replacement, but you will need a variety of tools, and you should have at least some rudimentary knowledge of automotive transmissions and mechanics.