I have a 2006 Toyota Corolla and the check engine

I looked up you code and your correct its your shift solenoid valve SL. And that code can be set by three different faults, so depending on whats causing that code to be set it can be expensive or not. The code can be set by a faulty valve, bad wiring, or the expensive part,sorry, it could be your Engine Control Module.

MONITOR DESCRIPTION Based on the signals from the Throttle Position Sensor, the Airflow Meter and the Crankshaft Position Sensor, the ECM sends a signal to the SL Solenoid Valve to regulate the hydraulic pressure and provide smoother gearshifts. The shift-solenoid valve SL responds to commands from the ECM. The valve controls the lock-up relay valve to perform the torque-converter lock-up function. If the ECM detects an open or short circuit for shift-solenoid SL, it will illuminate the MIL.