* Low Transmission Fluid: Low fluid level is a major cause of transmission problems. Without enough fluid, the clutch packs and other internal components can't engage properly, leading to the inability to select forward gears. Reverse often works because it uses a different set of clutch packs.
* Faulty Transmission Solenoids or Valve Body: These components control the flow of transmission fluid to engage the correct gears. A malfunctioning solenoid or valve body might allow reverse to function while preventing forward gears from engaging.
* Worn-out Clutch Packs or Bands: These are internal components that transfer power from the engine to the wheels. Wear and tear can prevent them from engaging properly, particularly in forward gears.
* Internal Transmission Damage: More serious damage, such as broken gears, a stripped shaft, or other internal failures, could selectively prevent forward gear engagement.
* Shift Linkage or Cable Problems (less likely in modern vehicles): While less common in electronically controlled transmissions, issues with the linkage or cable that connects the shifter to the transmission could interfere with gear selection.
* Faulty Transmission Control Module (TCM): The TCM is the computer that controls the transmission. A faulty TCM can prevent the transmission from shifting into forward gears.
What to do:
Don't attempt to drive the vehicle extensively if it's only going into reverse. Further damage to the transmission is possible. You should have the vehicle towed to a qualified mechanic or transmission specialist for diagnosis and repair. They will be able to determine the exact cause of the problem and provide the necessary repairs. Simply adding transmission fluid isn't a solution unless you know *for certain* that it's low, as adding fluid to a transmission with internal damage can worsen the problem.
