What causes an automatic transmission not to change gears

A vehicle transmission is a mystery to many motorists, and for a good reason. It is a complex mechanical part with many components fitted together. It becomes more complex if you own a manual transmission because it’ll keep you busy throughout your journey.

However, once you master how to shift manual gears effectively, it becomes second nature. This means you’ll be changing the gears without paying much attention. You must resist this for smooth operations. There are several reasons transmission will not engage in any gear, both in manual and automatic vehicles.

This article will discuss why transmission will not engage in any gears and the solutions to fix the problem. First, let’s start with the causes.

What Causes Transmission To Not Engage In Any Gear?

Here, let’s look at what causes a transmission not to shift into any gear. Any of the outlined causes below could be the reason.

Worn out clutch: Manual Transmission

A dragging or slipping clutch will stress out the transmission. Problems with the hydraulics or clutch pedal linkage could be the cause. If the clutch is worn out, allowing the transmission to slip, it can cause the tranny not to engage in any gear.

The clutch disc and pressure plate are clutch component systems that can wear over time and require replacement. If they wear out, it’ll cause the transmission to slip, lose power, and make it difficult to shift gears. If you notice any of these, you’ll have to check and replace these components if they’re the culprit.

Dirty transmission fluid: Automatic transmission

Transmission fluid plays a critical role in the proper functioning of automatic transmissions. In fact, the torque converter, an essential component of automatic transmissions, works on the principles of hydraulics.

With time, dirt, debris, and metal shavings will get into the transmission, affecting the hydraulic. These particles will cause the transmission to slip, lose power, shift hard from 1st to 2nd, or not engage in any gear.

Therefore, it is important to carry out scheduled transmission fluid changes at regular intervals. Read this article, “should I change transmission fluid at 100k miles,” to know when to change the transmission fluid.

Shift lock: Automatic transmission

If you own an automatic car, you’ll know what shift lock means. When you start an automatic car, the transmission won’t shift from the park to any gear unless you depress the brake pedal. The mechanism that sticks the gear lever until you depress the brake pedal is the shift lock.

This is a safety feature in automatic vehicles that prevents the car from rolling when a curious child tries to move the gear selector. However, this feature can malfunction and prevent the transmission from engaging in any gear.

Fortunately, many automatic transmissions feature a shift lock override. This lets you press down the shift lock and engage the vehicle even when the shift lock is malfunctioning. Visit your owner’s booklet to find out how yours works.

Bad Torque converter: Automatic transmission

In manual transmissions, the clutch systems engage and disengage the transmission unit from the engine. The torque converter does the same function on an automatic transmission.

The torque converter comprises three key components known as the pump, stator, and turbine. Any of these components can fail and cause hard shifting. When wondering, ‘what causes gears won’t engage,’ remember that a faulty torque converter can also prevent the transmission from engaging in any gear.

Bad transmission control unit: Automatic transmission

The transmission control unit (TCU), also known as a transmission control module (TCM), is a transmission computer that tells it when to shift gears efficiently. These components are only found in automatic transmissions.

If your car doesn’t move in any gear, an automatic transmission control module could be the cause. If you suspect the transmission control module to be the cause, insert your diagnostic tool to pull out the registered fault codes.

One of the common signs of a faulty TCM is that the car will display an incorrect gear position from the current gear the vehicle is running on the dashboard.

Other signs of a bad TCM are;

• The transmission won’t shift when accelerating
• Strange sounds when shifting to drive mode – the gears won’t change, yet the RPM increases.

Broken or dislodged transmission linkages

It’s possible for the linkage between the gear shifter in the cabin and the tranny unit to dislodge. This can happen both on manual and automatic transmissions. Though, it could be unlikely the cause.

This cable can disconnect by a rough bump or car accident. It can also deteriorate and break because of age.

If you were asking what causes automatic transmissions to fail to engage in any gear, you have seen why automatic and manual transmissions cannot engage in any gear.

What’s next?

Let’s look at the solutions to fix these problems.

How To Fix Transmission Engaging Problems

Since there are probable causes that will cause the transmission not to enter gear, there are several solutions as well. Let’s look at how to fix transmission problems.

Transmission fluid

Low transmission fluid will cause the tranny to overheat and underperform. Dirty or degraded fluid will lose its lubricating power and may cause the tranny not to engage in any gear.

If low or dirty transmission fluid is the reason, the transmission is not engaging, check the state of the fluid and act accordingly. Check the color of the fluid via the dipstick; if it is burnt or dirty, flush and refill it. If it is low, refill it.

Fixing worn clutch Issues

A worn clutch is the most common cause of manual transmission issues. A damaged throwout bearing, clutch disc, or pressure plate can prevent a manual transmission from engaging gears.

Replacing the defective clutch components is all you need to fix the engagement issues.

Connecting or replacing broken or dislodged transmission linkage

Transmission linkages connect the gear lever with the transmission unit. It can be springs or cables under the gear shifter console. If you suspect it, contact a mechanic to diagnose and do what is needed. Reconnecting or replacing it will fix the problem and keep your vehicle on the road again.

Replacing defective torque converter

The torque converter is the heart of automatic transmission. It plays a critical role in engaging and disengaging an automatic transmission. If it fails, it’ll cause your truck won’t move in any automatic transmission.

Of course, replacing it will fix the problem. However, it can fail in many ways. Therefore, I recommend you read this well-detailed article on the symptoms of a failed torque converter.

Replacing faulty TCM

If something goes wrong underneath the vehicle and the TCM cannot compensate, it will cause the transmission to malfunction. Again, the transmission control module can go bad and affect the smooth running of the vehicle. To track if the TCM is the culprit, diagnose the vehicle with a scanning tool.

FAQs:

Q: Why won’t my car move when I put it in drive or reverse?

Several factors can cause a vehicle not to move in drive or reverse. The primary cause of this malfunction is worn-out clutch components that don’t have enough materials to withstand the weight and friction of the vehicle.

Other probable causes of this malfunction are faulty shift lock, broken or dislodged transmission, low transmission fluid, bad torque converter, and lousy TCM.

Q: What does it mean when a car won’t go into gear?

Whether you have a defective manual gearbox or automatic transmission, your car may fail to go into gear at any time. This means you’ll be stranded wherever this happens until you track and fix the culprit.

Q: What causes a transmission to go in reverse but not forward?

There are three main reasons a transmission may only move in reverse and not forward. These include low transmission fluid, faulty speed sensors, and defective transmission components.

Low transmission fluid: If your transmission fluid is too low, it will prevent the tranny from shifting properly. It can also cause it to only move in reverse and not forward.

Faulty speed sensor: Take it or leave it; a faulty speed sensor can cause a transmission to move only in reverse gear. The speed sensor features a magnetic sensor that enables smooth gear shifting inside the transmission unit. It tells the car computer how fast the vehicle is traveling. If it fails, it will send a false signal to the car computer and prevent it from moving forward or reverse.

Faulty transmission components: There are several transmission components involved. A faulty transmission solenoid, a lousy computer that controls the car, or other defective internal components can prevent a vehicle from moving forward.

Q: What causes an automatic car not to move in drive?

As explained earlier, automatic transmissions function in hydraulic dynamics. They rely on the transmission fluid to work properly. If they run low on fluid, it’ll affect the smooth running. Whenever you shift into any gear, the car computer activates the transmission solenoid to allow fluid to flow into the valve body.

The transmission control unit, on its own, receives and processes the data from all tranny components. The speed sensor signals the TCM or PCM how fast the vehicle travels.

Therefore, a low transmission fluid, defective transmission solenoid, lousy speed sensor, faulty valve body, or bad TCM can prevent a vehicle from moving in the drive.

Q: Can a fuse cause transmission problems?

Of course, a blown a fuse can cause transmission problems. A fuse connects the transmission solenoid and the TCU. So, if any malfunctions or issues occur on these fuses, sensors, or associates, it’ll cause transmission problems.

Q: How much does it cost to fix engaging Transmission Problems?

The average cost of fixing transmission engaging problems ranges from $100 to $1000. If the culprit is a low or dirty transmission fluid, then you should budget to spend around $100 to $300 by buying a new fluid, flushing, and refilling the transmission.

If a faulty clutch is a cause in your manual transmission, it’ll cost around $400 to $1000 to replace the faulty components.

Final words

There are many reasons transmission will not engage in any gear. We have outlined the causes above and how to fix the problem. The most common amongst them is low transmission fluid.

When wondering, ‘why won’t my gear shift engage?’ Check the tranny fluid level and refill it to the recommended level if it’s below the gauge. A common top-up can fix the problem.

If the low fluid is not the problem, you can check the probable causes above. It’s recommended to fix issues on time before it escalates into major problems.