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Why Is My Automatic Car Not Shifting Gears?

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By NAPA
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Is your car not shifting gears like it used to? An automatic transmission makes driving much less complicated than the manual gear (stick shift) alternative. But that convenience comes at the price of complexity. When an automatic transmission equipped car won’t shift gears, there could be several potential issues. These issues can range from a simple fix to needing a complete transmission rebuild. Below is technical expertise on “Why is my automatic car not shifting gears?” 

Low Transmission Fluid
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Your automatic transmission relies on hydraulic fluid pressure to operate. The pump pulls

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from the transmission pan reservoir to actuate different components. If the transmission fluid level gets low enough, the pump will be unable to push fluid where it needs to go. Even worse, the pump will pull air into the system, which could lead to a lack of lubrication that damages parts. 

If you are lucky, your vehicle has a transmission fluid dipstick so you can easily check the fluid level according to the instructions in the owner’s manual. If your vehicle does not have a transmission fluid dipstick but is “

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”, that doesn’t prevent you from checking the fluid level. In most cases, the fluid can be checked via a fill plug, but the transmission has to be at a certain temperature and the vehicle must be level. This isn’t an easy task, so it might be best to have your local
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do it for you.

Faulty Shift Solenoid

We just mentioned how an automatic transmission relies on pressurized fluid to operate, but that fluid also needs to be routed to where it is needed. In a modern, electronically controlled automatic transmission, shift solenoids control the flow of transmission fluid. If the shift solenoid is faulty, then the fluid won’t be routed to the desired shift actuator. In older non-electronically controlled transmissions, shifting was controlled by shift valves, but the idea is the same. Shift solenoids can wear out or get stuck, leading to a no-shift condition. Fixing a faulty shift solenoid usually requires removing the transmission fluid pan to access the transmission valve body.

Low Transmission Fluid Pressure

You should be seeing a pattern of how important hydraulic fluid is to the operation of an automatic transmission. If the transmission fluid level is fine, there may still be a problem with the fluid pressure. Low fluid pressure can be caused by a worn out pump, clogged fluid passages or a clogged transmission fluid filter. A lack of shifting car gears due to low fluid pressure usually means it is time for a

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. If the problem is with the pump itself, then you are probably looking at a transmission rebuild.

Bad Transmission Control Module

Most modern automatic transmissions have an electronic

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(TCM). The control module takes input from various sensors, and decides how the transmission should react. Depending on where the control module is mounted, it can lead a very hard life. Extreme temperatures, vibrations, leaking fluids and sometimes even how the circuit board is built can all lead to failures of microchips and other electronic components. If the check engine light is on while you are having shifting problems, the TCM may be the issue.

Broken Shift Cable

Each time you drive, the shifter is moved at least twice, once for driving and again for park. That movement adds up over the years. While an automatic transmission doesn’t have the complicated shifting mechanism of a manual transmission, there is usually a physical connection between the shifter and the transmission. Modern

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usually have plastic components that can break down over time. There may also be bushings that get worn out. The shift cable itself is usually metal and rarely breaks, but the pieces connecting it to the transmission can possibly fail.

Shift Lock Engaged

If the car is not shifting into gear from park, then the issue might be the gear shift interlock. Most modern vehicles have a lockout on the automatic gear shifter that requires the brake pedal to be pressed first. If the brake pedal isn’t pressed, the shifter won’t move. It is possible that the brake pedal sensor doesn’t read that the pedal is pressed, or a break in the shift interlock circuit interrupts the connection. The shift lock can be

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.

Worn Out Bands

Just like how brake pads can wear out, so can the friction materials inside the transmission like the bands. Transmission bands hold certain components in place, while others are allowed to rotate. When this happens, the transmission won’t go into certain gears. Unfortunately worn out bands usually mean a complete transmission overhaul. Material from the worn out bands can make their way into sensitive fluid passages, clogging them or causing accelerated wear

Failed Throttle Sensor

This one may seem odd, but gauging how much throttle input the driver is giving makes a big difference in how the transmission acts. Whether the input is from a

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or a cable, if the driver pushes down the gas pedal, the transmission needs to change gears. But if that input isn’t received, the transmission has no idea what the driver wants to do. If the transmission doesn’t know the driver is hitting the gas, it might not shift into the next gear. Even worse, on some older transmissions, if the transmission isn’t linked correctly to the throttle input, severe damage can be done.

If your transmission isn’t shifting like it used to, simply head to your local

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center. Our team of ASE-certified technicians have the expertise and training to diagnose your automatic transmission issues. As a bonus, your repair is covered by our free 24-Month/24,000-Mile
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(parts and labor on qualifying repairs and services), which spans across the entire nationwide NAPA Network, including 17,000+ NAPA Auto Care center locations.

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