* Low Transmission Fluid (despite clean pan): Even if the pan looks full, there might still be low fluid due to an internal leak. Check the fluid level with the engine running and warmed up, using the proper dipstick method for your vehicle. Low fluid is a serious issue, as it can cause damage.
* Valve Body Problems: The valve body controls fluid flow within the transmission, directing it to the correct clutches and bands for each gear. A malfunctioning valve body (worn solenoids, stuck valves, etc.) is a common cause of transmission failure to engage gears. This requires a professional diagnosis and likely repair or replacement.
* Torque Converter Issues: The torque converter connects the engine to the transmission. A problem with the torque converter (e.g., internal failure, clutch slippage) can prevent gear engagement.
* Clutch Pack or Band Failure: The clutches and bands within the transmission engage the gears. Wear, failure, or damage to these components will prevent the transmission from shifting correctly.
* Electrical Problems: A faulty shift solenoid, wiring harness issue, or even a problem with the transmission control module (TCM) could prevent proper gear selection. A diagnostic scan tool is needed here.
* Low Line Pressure: The transmission needs sufficient fluid pressure to operate properly. A problem with the pump, pressure regulator, or other internal components can lead to low line pressure and gear engagement issues.
What you should NOT do:
* Continue driving: Driving with a malfunctioning transmission can cause significant and expensive damage. Towing is highly recommended.
* Attempt DIY repairs: Automatic transmission repair is complex and requires specialized tools and knowledge. Improper repair attempts can worsen the problem.
What you SHOULD do:
1. Have the transmission professionally diagnosed: A qualified mechanic specializing in automatic transmissions needs to inspect your vehicle. They will likely use a diagnostic scanner to check for trouble codes and assess the transmission's internal pressure and operation.
2. Get multiple quotes: Transmission repair can be expensive, so it's best to obtain quotes from several reputable shops before making a decision.
3. Ask about the diagnostic process: A reputable shop will explain their diagnostic process and what they're checking before recommending repairs.
Ignoring the problem will only lead to more costly repairs down the line. The sooner you get a professional diagnosis, the better.
