When my solenoid on my 300 started to fail the transmission would work fine and the next the car was driven the tranny did not work fine, it went into limp mode. Switching the car off and restarting a few times it would work fine again. This went on for awhile until it did not work fine at all. It was a slow drive to the dealership to get it fixed, my wife worked at the dealership and labor was $25/ hour, so it was not worth looking at myself. Parts were 10% over their cost.