My passenger side blade works fine, drivers side moves a little, goes up just a little bit. 2003 Subaru legacy AWD

The nylon bushings on the rods that connect the wipers go out.  

 

Pull the wiper arms

Pull the plastic cover that goes across the bottom of the windshield and under the hood

You will see the linkage and rods.  

 

You have to buy the complete rod as I have not found replacement bushings.  

 

Dealer or Junk yard.

It also might be as simple as snugging down the nut under the rubber plug on the bottom of the arm. The parts are made of softer metal and will "strip" a little if the blade has been frozen or pushed heavy snow on the windshield.

Thanks, it was simply the bolt had come loose. Easy and free to fix.