Why can the car start normally but cannot shift gears?

[WyattFitz]

There are several reasons why a car cannot shift gears after starting, including incomplete clutch disengagement, deformation of the gearshift linkage mechanism, and gear lock. Location of the clutch: The clutch is located inside the flywheel housing between the engine and the transmission. The clutch assembly is fixed to the rear plane of the flywheel with screws, and the output shaft of the clutch is the input shaft of the transmission. Function of the clutch: The clutch allows gradual engagement between the engine and the transmission to ensure smooth starting of the car. It temporarily disconnects the connection between the engine and the transmission to facilitate gear shifting and reduce impact during shifting. It also acts as a separator during emergency braking to prevent overload of the transmission and other drivetrain components, providing a certain level of protection.

[McEmilio]

I've been driving for over a decade and have encountered several instances where the car started normally but couldn't shift gears, mostly with automatic transmissions. The reasons can vary: for manual transmissions, if the clutch pedal is too stiff or too soft, it indicates a failure in the clutch master or slave cylinder, or severe wear on the clutch disc, preventing power transmission. For automatic transmissions, it's more common and requires checking if the brake pedal is pressed, as the gear shift safety system relies on the brake signal. If the brake light switch is faulty or the brake isn't fully depressed, shifting gears becomes impossible. Additionally, if the transmission fluid level is too low or too dirty, clogging the channels, it can cause gear shifting to stick. I recommend first trying to press the brake pedal firmly a few times to see if it unlocks. If that doesn't work, then check the transmission dipstick level under the hood. Never force the gear shift to avoid damaging the internal gears of the transmission. Safety first—if you can't figure it out, contact roadside assistance immediately and have the car towed to a professional repair shop to inspect the electronic control unit or hydraulic system. Regular maintenance, including cleaning the transmission, can prevent such issues.