What does the access lid on the left side of the rear part of the trunk floor access? I could not find a reference in the manual. Thanks for your answers.

 

You mean the rear fuse panel?

 

Perhaps if you take a picture we can help quicker.

 

On my car, that panel is used to access the USB-powered audio switchbox for the integrated CarPC.

On JohnnyCake's car, that panel is used to access the battery module for his cell-phone controlled remote system.

But, on your car, it's probably just covering up the rear fuse panel.