1. Low transmission fluid: Check the transmission fluid level and top it off if it's low.
2. Faulty shift linkage: The shift linkage is the mechanism that connects the gearshift lever to the transmission. If the shift linkage is damaged or loose, it can prevent the transmission from shifting properly into fourth gear.
3. Synchronizer problems: Synchronizers are components of the transmission that help smooth the shifting process. If a synchronizer is damaged or worn out, it can make shifting into fourth gear difficult.
4. Transmission damage: In some cases, a transmission may become internally damaged, which can prevent it from shifting into certain gears.
If you've checked the transmission fluid level and inspected the shift linkage, but the problem persists, it is recommended to have a professional mechanic inspect the transmission to determine the exact cause of the issue.
