When your car won’t go into gear, it can cause serious problems. What’s the trouble? It could be any number of things, depending on whether you have a manual transmission or an automatic transmission. Here’s a rundown of some of the possible problems, and what to do about them.

Manual Transmission Gear Problems

If you drive a stick shift, you may find that when you press the clutch, the gear shift still won’t move. The problem might be that the clutch is simply worn out. After a while, there’s no longer enough friction to transfer power from the engine to the wheels.

On average, the clutch on a stick shift wears out every 60,000 miles or so—depending on how and where you drive it. Fortunately, replacing it is a fairly routine procedure, which your mechanic should be able to perform relatively quickly.

There also may be an issue with the clutch master cylinder, and the hydraulic fluid contained therein. If the clutch goes all the way to the floor, then this may be the problem. If the cylinder leaks, eventually there won’t be enough hydraulic fluid to put the car into gear. In this case, the clutch master cylinder will need to be replaced.

Automatic Transmission Gear Problems

Automatic cars can have problems shifting into gear as well. In this case, there’s a good possibility the issue is an electronic one. Most of the mechanisms that tell a car to shift gears automatically are electronic, rather than mechanical. If the electronic signals aren’t being sent or received properly, it can keep the valves that control the flow of transmission fluid from opening or closing—which then keeps the car from going into gear.

Or the issue could be with the shift interlock mechanism. The mechanism is designed to keep you from accidentally shifting to Neutral or Park while the car is in motion. As you’re no doubt aware, you can’t put your car into Park unless the engine is running and both the break pedal and the button on the side of the gear shift are being pressed.

However, if you’re doing all of that, and the car still won’t shift into drive, try pressing the shift lock release button. It’s a small button, usually right next to the gear shift. There may be a small covering over the button, to prevent it from being pressed accidentally. Remove the cover and use a small, narrow object, such as a key or a screwdriver, to press the button. Then, depress the brake and shift gears as you normally would.

If this doesn’t solve the problem, or if the gear shift continues to lock going forward, then talk to your mechanic. You may need a new brake pedal position sensor, or there may be a transmission problem.

Transmission Fluid

This is an issue that can plague either a manual OR automatic transmission. The transmission fluid is what allows the gears to shift smoothly. Over time, dirt, grease, and other contaminants can build up in the fluid, causing it to turn from bright red to a brown or black sludge. This sludge is hard on your gears, and should be flushed out and replaced with new transmission fluid. As a general rule, replace your transmission fluid every two years or 30,000 miles.

There may also be a leak, which means there’s not enough fluid in your transmission—which also wreaks havoc on your gears. In this case, your fluid needs to be replaced—as soon as the leak is repaired, of course.

With regular upkeep to your vehicle, and regular service to your transmission when needed, you can prevent a lot of these problems and keep your gears shifting smoothly. Talk to your mechanic to see what your car needs to help it continue running optimally, and avoid costly repairs.