Reasons Why an Automatic Transmission Car Cannot Accelerate Beyond 40 MPH

[LeCora]

An automatic transmission car's inability to accelerate beyond 40 MPH may be caused by insufficient engine acceleration or transmission failure. The specific diagnostic methods and solutions are as follows: Diagnostic method for insufficient engine acceleration: Park the car on level ground, place the transmission lever in the P position, engage the parking brake, and then press the accelerator pedal to check the engine's acceleration performance. If the engine speed increases slowly or cannot rise beyond a certain RPM, the issue is likely caused by engine problems. Check whether the fuel supply pressure and cylinder pressure are normal, and whether the fuel injection system and various sensors are functioning properly. Transmission failure: This could be due to severely worn or burnt friction plates in the transmission, or malfunctions in the transmission valve body's shift valves, solenoid valves, transmission control computer, or related circuits, resulting in difficulty in upshifting and acceleration. After identifying the corresponding fault, it is advisable to leave the repair and handling to professionals.