Recently had my "Brake Pad Wear" light activated. I'm sure it's accurate as I've put 90,000 miles on this car (purchased it with 30,000 miles) and I've never had to put brakes on it. It seems the rotors are ok, and I'll start with the pads. My question is: I know the brake pad sensor needs to be replaced as well. If it is only one of the sensors that is tripping the indicator light, do I still need to replace all 4? If not, how can I determine which one is active and replace that one?