What causes an automatic transmission to get stuck in first or reverse gear?

An automatic transmission may get stuck in first or reverse gear due to several factors, including low Transmission Fluid levels, which can lead to insufficient hydraulic pressure. Additionally, issues such as a malfunctioning shift solenoid, a faulty valve body, or problems with the transmission control module can prevent proper gear shifting. Mechanical failures within the transmission, such as worn clutch packs or broken bands, can also contribute to this issue. Regular maintenance and timely fluid changes can help mitigate these problems.