Normally Open Shift Solenoid Valves

Three of the shift solenoid valves used in the AF33-5 (the reverse, 1st SS valve; the 2-3, 3-4 SS valve; and the 3-4, 4-5 SS valve) are referred to as normally open solenoid valves. Normally open shift solenoid valves are de-energized (turned OFF) when the TCM opens the path to ground for the solenoid's electrical circuit. With the solenoid OFF, signal fluid moves the metering ball and plunger away from the exhaust seat. This allows signal fluid to flow past the metering ball and exhaust through the solenoid. As a result of this exhaust, there is no pressure in the signal fluid circuit when the normally open solenoid is OFF. When the TCM provides a path to ground for the electrical circuit to energize (turn ON) the solenoid, current flows through the coil assembly in the solenoid and creates a magnetic field. The magnetic field moves the plunger inside the solenoid and seats the metering ball against the exhaust seat, thereby blocking the exhaust passage and causing signal fluid pressure to increase.