Pressure Control Solenoid

The Pressure Control solenoid, controlled by the TCM, is a precision electronic pressure regulator that controls the line pressure. The Pressure Control solenoid operates at approximately 600 Hz (cycles per second) and regulates the feed limit fluid pressure into the throttle signal fluid circuit. The TCM controls the pressure by varying the current at the solenoid coil. The varying the duty cycle of the solenoid controls the amount of current. A greater duty cycle creates a higher current at the solenoid. Similar to the Band Apply solenoid, the duty cycle represents the percentage of time that the current flow energizes the coil. The high frequency of the Pressure Control Solenoid acts to smooth the pulses that are created by the duty cycle.

The duty cycle and the amount of the current flow to the force motor are mainly affected by the throttle position. Both the current flow and the duty cycle are inversely proportional to the throttle angle. As the throttle angle increases, the duty cycle is decreased by the TCM which decreases the current flow.

The current flow to the solenoid creates a magnetic field that attracts the armature, thereby moving the plunger against the spring force. Note that the pressure Control Solenoid is assembled with some transmission fluid inside. This fluid assists the damper spring in cushioning the armature movement.

At minimum throttle (idle), the duty cycle is at maximum and current flow approaches 1.1 amps (fully on). This forces the armature against the plunger and compresses the spring. Therefore, throttle signal fluid pressure acting on the end of the Pressure Control Solenoid valve moves the valve towards the armature and blocks the feed limit fluid circuit. The throttle signal fluid circuit is then open to an exhaust port and the throttle signal fluid pressure is at a minimum.

At maximum throttle, the duty cycle is at a minimum and the current flow approaches 0.1 amps (fully off). Therefore, the magnetic field is a minimum and the spring force holds the plunger, the armature and the valve against the throttle signal fluid pressure acting on the end of the valve. This closes the exhaust port and opens the throttle signal fluid circuit to the feed limit fluid, creating maximum throttle signal fluid pressure.

Under normal operating conditions between the maximum and minimum throttle positions, the TCM varies the duty cycle which varies the current flow to the Pressure Control Solenoid between approximately 0.1 and 1.1 amps in order to control the throttle signal fluid pressure. This regulates the valve between opening and closing the exhaust port in order to regulate the throttle signal fluid pressure. The throttle signal fluid pressure then controls the line pressure at the pressure regulator valve accordingly. If the electrical system becomes disabled for any reason, the current flow will be 0.0 amps and the Pressure Control Solenoid will allow maximum throttle signal fluid pressure. This creates maximum line pressure in order to prevent any apply components from slipping until the condition can be corrected.

The throttle signal fluid pressure also acts on the accumulator valve in order to increase the accumulator pressure, and the apply rate of the clutches and bands as the throttle angle increases. Remember that with greater accumulator fluid pressure, there is less cushion for clutch apply fluid.

Approximately every 20 seconds the TCM pulses the Pressure Control Solenoid at either maximum (100 percent duty cycle) or minimum current flow (0 percent duty cycle) depending on the Pressure Control Solenoid operating conditions. These pulses prevent possible contamination from sticking the Pressure Control Solenoid valve or plunger in any given position.