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Solenoid valve ST, for system pressure

Solenoid valve ST, for system pressure


Solenoid valve ST is located in the valve housing, which is mounted on the gearcase. The solenoid regulates the automatic transmission's system pressure.

The solenoid is controlled by a 300 Hz PWM signal via control module pin 40 and is grounded via pin 38. It is controlled by the varying current that is the result of the prevailing pulse ratio. When the pulse ratio is high, i.e. high current strength (approx. 1 A), the system pressure is low and when the pulse ratio is low, i.e. low current strength, the system pressure is high. In case of an open circuit, system pressure will be at maximum. The valve is then fully open.

The control module uses bus information on the current “Engine torque”, unit Nm, and the gear currently engaged to control system pressure.

The winding resistance in the solenoid is about 4 Ohm.

At idling speed, with the handbrake applied and the selector lever in position D, current strength is approx. 900 mA and system pressure 3.4-4.6 bar.


Diagnostics

In the event of a fault in the solenoid, diagnostic trouble code P0748 will be generated and the transmission will go into Limp-Home mode.