What line am I looking at?
 

Have a question for the group. Canadian A4 Avant Quattro, left side of the car there's 3 steel lines. 2 are same size and assumed to be rear brakes.

The 3rd is larger, maybe 5/16" or 8mm. It's been flattened. I'm thinking fuel delivery, as I'm getting the P0089 low fuel pressure code.

Any help is appreciated

Also, is there an online parts fiche one can access?

Thanks.