Common symptoms of wear or failure that help to identify shift control solenoid malfunctions include the illumination of the check engine light and shifting problems with an automatic transmission. Shifting problems may take the form of erratic shifting, an inability to downshift, or a severe delay in shifting that leaves your vehicle stuck in neutral. Be cautious of an improper diagnosis of wiring and sensors, as this can cause unneeded replacement of shift solenoids.
Electrical issues and dirty fluid can cause changes in the transmission fluid pressure that lead to solenoid problems. Erratic shifting is when the gearbox can skip a gear in either direction, repeatedly shift between gears, or get jammed. Dirty fluids sometimes cause a shift solenoid to become stuck in the open or closed position. If the solenoid is stuck, fluid can't enter the transmission valve body and pressurize the appropriate gear. The way to recognize this problem is to check for an inability to downshift.
Solenoid problems can delay gear engagement, either because the solenoid is stuck or because electrical problems are sending too much or insufficient electricity. In most cases, solenoid issues trigger an error code that lights up the check engine light. This is because solenoids are a part of the electrical system that runs through a vehicle. Use a scan tool to access the error codes in the electrical system that identify the specific problem.