Normally Closed Shift Solenoid Valves

WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The remaining two shift solenoid valves used in the AF23-5 (the 1-2, 2-3, reverse SS valve and the reverse SS valve) are referred to as normally closed solenoid valves. Normally closed shift solenoid valves function similar to normally open shift solenoid valves in that the TCM controls the path to ground for the electrical circuit to turn the solenoid ON or OFF. The normally closed shift solenoid valves are de-energized (turned OFF) when the TCM opens the path to ground for the solenoid's electrical circuit. However, when a normally closed solenoid is OFF, spring pressure seats the plunger and metering ball against the exhaust seat, thereby blocking the exhaust passage and causing signal fluid pressure to increase. 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 against spring force and moves the metering ball 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 closed solenoid is ON.