Either or. I believe the most pads on the aves have sensors on all 4 pads. if only 2 have sensors then make sure 1 sensor per side if stated before. Be sure to make sure everything is nice and tight. Whenever I do any brake jobs I always use lock tight. I had a vehicle in the shop where the caliper bracket bolt had vibrated out after the customer had done the job themselves. When I was calling the dealer to get a replacement bolt he told me that it happens all the time where they vibrate out like that. Ever since hearing that story I apply lock tite. After, be sure to torque tires back down. lugs on most 1500's are 140ft lbs. If you're unsure about something don't hesitate to ask. A brake job is far from difficult, but its not something you want to do wrong and put yourself, and everyone on the road with in danger.