What does the solenoid do? [SOLVED]

Transmission solenoid(s) are mainly located internally in automatic transmissions. Some manufacturers have them located externally as well. The solenoids are controlled by either the Transmission Control Module (TCM) or the Engine Control Module (ECM). By turning them on or off at the correct time based on engine RPM and road speed, the transmission shifts by redirecting transmission fluid through the transmission valve body’s fluid circuits to apply or release transmission bands, drums or clutches.

If the solenoid sticks mechanically, it can’t control the fluid circuit properly resulting in shift failures or slipping.

Trans Tune cleans sticky residues from solenoids, helping to keep the transmission shifting properly.