Electronic Transmission

On most vehicles, PCM controls transmission and other vehicle functions. PCM monitors a number of engine/vehicle functions and uses data to control shift solenoid "A", shift solenoid "B", TCC solenoid and the force motor. PCM also regulates TCC engagement, upshift pattern, downshift pattern and line pressure (shift quality).

• Shift Solenoid "A" (1st-2nd)
  
  Shift solenoid "A" is attached to the valve body and is a normally-open exhaust valve. PCM activates solenoid by grounding it through an internal quad-driver. Solenoid "A" is on in 1st and 4th gears, but off in 2nd and 3rd. When on, solenoid redirects fluid to act on the shift valves.
• Shift Solenoid "B" (2nd-3rd)
  
  Shift solenoid "B" is attached to the valve body and is a normally-open exhaust valve. PCM activates solenoid by grounding it through an internal quad-driver. Solenoid "B" is on in 3rd and 4th gears, but off in 1st and 2nd. When on, solenoid redirects fluid to act on the shift valves.
• Force Motor (Pressure Control Solenoid)
  
  Force motor is attached to valve body and controls line pressure by moving a pressure regulator valve against spring pressure. Force motor replaces throttle valve or vacuum modulator used on past transmissions. PCM varies line pressure based upon engine load. Engine load is calculated from various inputs, especially TP sensor. Line pressure is actually varied by changing amperage applied to force motor from zero (high pressure) to 1.1 amps (low pressure). Force motor is periodically pulsed to prevent fluid contamination or varnish from causing pressure regulator valve to stick.