my ford mondeo radio r6006e?

Error E4 is Focus Error.

This can be due to a CD inserted incorrectly(upside-down) or dirtyetc....If so try a different CD.

Alternatively it might be due to a dirty laser . If so then purchase a CD Cleaning kit (Off Ebay or elsewhere) This is basically a CD disc with built in brushes which clean the laser surface.

RegWorts
June 2008