* Low Transmission Fluid: This is the *first* thing to check. Critically low fluid can cause all sorts of shifting problems. Check the fluid level with the engine running and warmed up (according to your owner's manual). If it's low, immediately add the correct type of automatic transmission fluid (ATF) for your Aspire. *Do not overfill.* Low fluid might be caused by a leak – inspect the transmission pan and surrounding areas for signs of leakage.
* Transmission Solenoid(s): These electrical components control the shifting within the transmission. A faulty solenoid can prevent the transmission from shifting into higher gears. Diagnosis requires either specialized tools or a mechanic with experience. They often exhibit other shifting problems before completely failing to engage the highest gear.
* Valve Body Issues: The valve body is the "brains" of the transmission, controlling fluid flow to engage the different gears. Internal wear, blockages, or damage within the valve body can prevent proper shifting. This is often more expensive to repair.
* Torque Converter Problems: While less likely to cause *only* the highest gear to fail, a problem with the torque converter can prevent proper power transfer and shifting. This is a significant repair.
* Transmission Computer/Sensor: A faulty transmission control module (TCM) or sensor could be sending incorrect signals to the transmission, preventing it from shifting correctly. This requires specialized diagnostic tools.
* Clutch Pack Wear/Failure (Inside the Transmission): Internal wear on the clutch packs that engage the highest gear is possible, but usually comes with other symptoms.
What to do:
1. Check the transmission fluid level and condition immediately. This is the quickest and cheapest check. Dirty, burnt-smelling fluid is a bad sign.
2. If the fluid level is low, add the correct fluid, and check for leaks.
3. If the problem persists, take your Aspire to a qualified mechanic specializing in automatic transmissions. They have the diagnostic tools and expertise to pinpoint the exact cause and recommend the best course of action, which may range from a simple repair to a complete transmission rebuild or replacement. Describing the symptoms clearly to the mechanic is crucial.
Trying to diagnose and fix a transmission problem yourself is generally not recommended unless you have significant mechanical experience. Improper repair can exacerbate the problem and lead to significant costs. Get professional help to avoid further damage and costly repairs.
