* Valve Body Problems: The valve body is the "brain" of the transmission, controlling fluid flow to engage different gears. A malfunctioning valve, worn valve body components, or a blockage within the valve body could prevent the transmission from shifting into higher gears. This is a common culprit in automatic transmission issues.
* Shift Linkage or Cables (if applicable): While less likely given the age and type of transmission, a broken or misadjusted shift linkage or cable (if your model uses cables rather than purely electronic controls) could prevent the transmission from receiving the correct shift commands.
* Governor Problems: The governor regulates shift points based on engine speed. A faulty governor could cause the transmission to stay in low gear, although this is less likely given the reverse functionality.
* Low Transmission Fluid (though less likely): While you mentioned it *might* not be this, low fluid *could* contribute to poor shifting. Check the fluid level using the dipstick. However, if it's low and it's still engaging reverse, there might be a significant leak elsewhere. *Note that the fluid color and smell should also be checked. Burnt fluid indicates significant internal damage.*
* Internal Transmission Problems: This is the worst-case scenario. Worn clutches, bands, or other internal components can prevent the transmission from shifting correctly. This often requires a major repair or replacement.
* Solenoids (if applicable): Electronic solenoids control fluid flow within the transmission. A faulty solenoid could prevent the proper engagement of higher gears.
What you should NOT do:
* Don't keep driving it: Continuing to drive the car in this condition will likely cause further damage to the transmission.
What you SHOULD do:
1. Check the transmission fluid level: Make sure it's at the correct level and that the fluid isn't burnt or discolored.
2. Have it professionally diagnosed: Given the symptoms, this is absolutely crucial. A qualified mechanic with experience in automatic transmissions can properly diagnose the problem and recommend the best course of action (repair or replacement). Trying to fix this yourself without the proper knowledge and tools is strongly discouraged.
3. Be prepared for a significant repair cost: Automatic transmission repairs can be expensive.
Ignoring the problem will only lead to greater expense and potentially render the transmission unrepairable. Get it to a mechanic ASAP.
