Here's a breakdown of why:
* Valve Body Issues: The valve body within the transmission controls the flow of fluid, directing it to different clutch packs to engage the correct gears. If the valve body is worn, damaged, or has a sticking valve, it could allow reverse to engage even when the gear selector is in another position, especially when the transmission fluid is warm and thinner. Internal wear and tear increases with age and temperature.
* Reverse Lockout Solenoid/Switch: This component prevents the car from accidentally shifting into reverse while driving forward. If this solenoid or the related switch is faulty, it might fail to disengage reverse when it shouldn't, again exacerbated by the warmth of the transmission fluid.
* Transmission Linkage (Less Likely): While less probable with this symptom, there's a small chance the linkage connecting the gear selector to the transmission itself is misaligned or damaged. However, this would likely manifest more inconsistently, not solely when the engine is warm.
* Wiring Harness Issues (Also Less Likely): A short or faulty connection in the wiring harness could theoretically cause this, but it's less common than mechanical problems within the transmission itself.
What NOT to do:
* Do NOT drive the car. This is extremely dangerous. You could cause significant damage to the transmission or even cause an accident.
What to do:
* Have it towed to a reputable transmission specialist or mechanic immediately. Attempting DIY repairs on a transmission is usually not recommended, especially for a problem as serious as this. A professional will need to diagnose the exact cause and recommend the appropriate repair (likely involving a transmission rebuild or replacement).
* Do not attempt to add any transmission fluid. Adding fluid won't solve the underlying mechanical problem and could even worsen it.
The warmth of the engine significantly points to a problem related to fluid pressure and temperature influencing components within the transmission itself. This is not a minor issue and needs immediate professional attention.
