What Causes a Transmission Not To Shift?

Can you imagine driving your car without shifting your gear at least once? You probably won’t even be able to move your car out of the driveway if your transmission won’t shift from park or neutral.

Whether you drive an automatic or a manual vehicle, it’s important to always make sure your transmission is in top shape. If it isn’t, you’ll need to figure out what’s preventing your transmission from shifting as soon as possible.

Why Your Automatic Transmission Won’t Shift

Unfortunately, answering the question “Why is my automatic car not shifting gears?” isn’t going to be easy. A lot of things can go wrong with your automatic transmission, so figuring out why is going to take a while, but you can start with some of these common causes:

Low or Dirty Transmission Fluid

Is your transmission slipping while your engine is revving high? If it is, then you might be dealing with low or dirty automatic transmission fluid (ATF). ATF helps power and protect your transmission, so if it leaks from a damaged cooler line or gets dirty, then your car probably won’t shift.

Malfunctioning PCM

A lot can go wrong if your vehicle’s powertrain control module (PCM) suddenly stops working, and your automatic transmission is one of them. Your PCM constantly uses information like your engine’s speed and throttle position to operate your automatic transmission, so if it glitches or malfunctions, then your transmission probably won’t go into gear.

Other Electrical Issues

If your PCM is working perfectly, then you might be dealing with other electrical issues. Your automatic transmission relies on different sensors, switches, and electrical wiring to function, so if a wire short-circuits or a sensor gets clogged, then your transmission might stop working too.

Shift Lock

Today, most automatic vehicles come with a shift lock safety mechanism that prevents the transmission from shifting out of park unless the driver is properly seated with their foot on the brake. It’s a great safety feature that prevents kids or pets from accidentally shifting the gear, but it isn’t perfect.

In some cases, it can malfunction and prevent you from shifting into gear and driving your vehicle. Thankfully, overriding this safety feature usually just requires inserting your key into a slot somewhere on your center console.

Bad Torque Converter

As its name suggests, the torque converter converts torque from the engine into hydraulic pressure that your transmission uses to shift gears. If the torque converter fails, your transmission can slip out of gear. You might also notice your vehicle vibrating even when you aren’t driving fast.

Broken Transmission Linkage

If your car won’t shift gears, then there’s a chance that you might be dealing with a broken linkage. Sometimes, accidents or bumpy roads can cause the linkage between the shifter in the cabin and the transmission to disconnect.

Why Your Manual Transmission Won’t Shift

A bad transmission is bad news, especially if you often drive on highways and busy roads. For your own safety, it’s best to diagnose a faulty manual transmission as soon as possible. Here are some common causes to consider:

Worn-Out Clutch

If your manual transmission won’t shift, then the culprit might be a worn-out clutch. Issues with the clutch pedal linkage can cause your clutch to drag and put extra strain on your transmission.

In some cases, you might be dealing with a bad clutch disc, which can wear out on some manual vehicles. It can cause your transmission to slip and lose power, so you’ll want to replace a faulty clutch disc as soon as possible.

If it is the clutch, one thing you can do to still be able to move the vehicle is with the vehicle off, put your shifter in gear, and start the vehicle. It should automatically start driving forward or backward depending on what gear you put it in. If you are doing this, be careful because pushing in the clutch will not stop the vehicle. You’ll also need to turn off the key.

Dirty Transmission Fluid

When was the last time you changed your transmission fluid? Manual transmissions need manual transmission fluid (MTF) to function properly. Unfortunately, MTF can also break down over time from a buildup of dirt, debris, and other particles.

Dirty MTF won’t just stop your transmission from shifting into gear. It’ll end up wreaking havoc on your transmission too. Luckily, replacing MTF isn’t complicated or pricey, so you can do it as soon as possible.

Generally servicing the manual transmission fluid is done by removing the drain plug and the fill plug. The fluid will drain pretty fast, especially once the fill plug is pulled. After, pump the fluid into the fill hole until it runs out of the hole. Then you can put the drain plug back in.

Broken Transmission Linkage

Just like an automatic transmission, your manual transmission can fail if the transmission linkage breaks. It isn’t one of the more common culprits of a manual transmission not shifting, but it can still happen if you drive over rough roads often.

Faulty Clutch Master Cylinder

Manual vehicles typically come with a clutch master cylinder, which is responsible for converting the mechanical movement of the clutch pedal to hydraulic pressure. In other words, it helps send hydraulic fluid back to the slave cylinder, so you can disengage the clutch from your transmission.

If the clutch master cylinder fails, this is bad news for your transmission. The clutch pedal will start to feel easy to press, and you’ll soon find it hard to shift gears.

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: The clutch master is generally on the firewall near the brake booster. Meanwhile, the slave cylinder can be external on the transmission or inside the bell housing, which requires removing the transmission to service it.

Bad Synchronizers

If your car starts making unusual grinding noises whenever you try to switch gears, then you might want to check your synchronizers. Synchronizers help your transmission shift gears smoothly, but they can wear over time from aggressive shifting and heavy-footed driving.