Automatic Transmission Pressure Control Solenoid Valve

Fig 1: View Of Pressure Control Solenoid Valve

Courtesy of GENERAL MOTORS CORP.

The pressure control (PC) solenoid valve is a precision electronic pressure regulator that controls the transmission line pressure. This control is based on the flow of current through the coil windings of the valve. As the flow of current is increased, the magnetic field which is produced by the coil moves the solenoid's plunger further away from the exhaust port. Opening the exhaust port decreases the output fluid pressure regulated by the PC solenoid valve, which ultimately decreases line pressure.

The TCM controls the PC solenoid valve based on various inputs, including throttle position, fluid temperature, MAP sensor, and gear state.

The TCM controls the PC solenoid valve on a positive duty cycle at a fixed frequency of 614 Hz. Duty cycle is defined as the percent of time current is flowing through the solenoid coil during each cycle. A higher duty cycle provides a greater current flow through the solenoid. The high, positive, side of the PC solenoid valve electrical circuit at the TCM controls the PC solenoid valve operation. The TCM provides a ground path for the circuit, monitors average current and continuously varies the PC solenoid valve duty cycle to maintain the correct average current flowing through the PC solenoid valve.

The resistance on the PC solenoid valve should measure between 3-5 ohms at 20°C (68°F).