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Solenoid valves, SLS and SLT for system pressure

Solenoid valves, SLS and SLT for system pressure


Solenoid valves SLS and SLT are located in the valve body, which is mounted on the gearbox. The solenoids govern the transmission system pressure. SLS governs the clutch disc pressure.

The solenoids are controlled by a 300 Hz PWM voltage via pin 26 (B) (SLS) and pin 35 (B) (SLT) on the control module. The solenoids are grounded via pin 36 (B) (SLS) and pin 15 (B) (SLT). They are controlled by a current that changes primarily in relation to accelerator position. A high pulse ratio producing a high current (approx. 1 A) results in a low system pressure. A low pulse ratio producing a low current results in a high system pressure. An open circuit produces maximum system pressure. The valves are 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.

Resistance of the windings of solenoid SLS and SLT is normally 5.1 - 5.5 Ω at 20°C.


Diagnostics

Diagnostic trouble code P0748 will be generated and the transmission will go into limp-home mode in the event of a fault in the SLT solenoid.

Diagnostic trouble code P0785 will be generated and the transmission will go into limp-home mode in the event of a fault in the SLS solenoid.