2009 Mercury Mariner Check engine

This is a fault light indication, You need to get a diagnoses scan done to reads the set codes, these codes will indicate the problem you have, get this done first and post back the readings, the codes will be a Pxxxx code that is a P with 4 digits eg P0302 would be a cylinder misfire code.

These are both related to the torque converter lock up clutch, often is the case that the cock up solenoid in the transmission has failed.

If a torque converter clutch fails and stays in the lock up position, you would notice a difficulty from driving off from a stop, it would be like trying to drive off in a to higher gear, you will see a higher fuel usage, the solenoid is not a huge problem to fix, I would go get a few quotes and I would fix it sooner than later as long term lock up will stress components and a further problems may present.