Line Pressure Solenoid (SL Solenoid)
Purpose:
The linear pressure solenoid regulates the pressure of the working fluid in the automatic transmission housing, which is transmitted to the valve body and torque converter. Pressure is adjusted to ensure proper gear shifting, smooth transitions and prevent transmission damage.
Location:
In Subaru automatic transmissions, the line pressure solenoid is usually located in the upper part of the transmission housing, next to the hydraulic module.
Working principle:
* When the engine is running and the transmission is engaged, the transmission control unit (TCU) sends an electrical signal to the line pressure solenoid.
* The signal opens or closes the solenoid valve inside the solenoid.
* When the valve is open, pressurized fluid flows through the solenoid into the automatic transmission hydraulic system.
* Fluid pressure is controlled by the amount of current supplied to the solenoid.
*When the valve is closed, the hydraulic system pressure is limited or released.
Possible faults:
* Dirty Solenoid: Contamination can prevent the valve from working properly, resulting in faulty shifting.
* Faulty Solenoid Valve: The coil or contact points may fail, causing the valve to continually open or close.
* Electrical Problems: Opens or shorts in the wiring can cause the solenoid to not receive proper power.
* Mechanical Damage: Damage to the solenoid housing or valve may cause pressure leakage.
Symptoms of a faulty line pressure solenoid:
*Hard Shifting: Rough shifting may indicate insufficient fluid pressure.
*Transmission slipping: Slipping can be caused by too high or low fluid pressure.
*Transmission Fluid Leaks: Fluid leaks can cause pressure loss and shifting problems.
*Transmission Control Unit (TCU) Trouble Code: Line Pressure Solenoid may be indicated by Trouble Codes stored in the TCU.