* Low or Failing Transmission Fluid: This is the first thing to check. Low fluid can cause all sorts of problems, including gear slippage and inability to shift. Check the fluid level (with the engine running and warmed up) and its condition. Dark, burnt-smelling fluid indicates serious internal damage.
* Faulty Shift Linkage/Cables: While less likely to cause it to *only* be stuck in low, a problem with the linkage or cables could prevent the transmission from shifting correctly. Inspect for broken or frayed cables, and check the linkage for proper movement and adjustment.
* Internal Transmission Problems: This is the most likely culprit. Several internal components could be failing, causing the transmission to stay in low gear:
* Broken or Worn Gears/Clutch Packs: These are the components that actually engage the gears. Wear and tear, or damage from low fluid, can lead to failure.
* Valve Body Problems: The valve body controls the flow of fluid within the transmission, dictating which gears are engaged. A problem here could prevent shifting.
* Broken or Worn Shift Solenoids (if electronically controlled): These are electromagnets that control fluid flow within the transmission.
* Low/Failing Torque Converter: The torque converter transfers power from the engine to the transmission. A problem here can severely impact shifting.
What to Do:
1. Check the transmission fluid: This is the easiest and cheapest check. If low, add the correct type of ATF (Automatic Transmission Fluid) specified for your car's transmission. If it's dark, burnt, or smells bad, you likely have internal damage.
2. Inspect the shift linkage/cables: Look for anything obvious like broken cables or binding linkages.
3. Professional Diagnosis: If the fluid is low or bad, or if the linkage/cables are fine, you *absolutely* need to take the car to a qualified transmission specialist or mechanic. Attempting to repair the transmission yourself is extremely difficult and could lead to further damage. A proper diagnosis involves inspecting the internal components of the transmission, which requires specialized tools and knowledge.
Expect a significant repair cost. Transmission repairs are expensive. Depending on the extent of the damage, you might be looking at a major overhaul or even a transmission replacement. Getting multiple quotes from reputable shops is advisable. Consider the age and overall condition of the vehicle before investing heavily in repairs.
