Symptoms
A grinding or scraping sound on the first few stops, a pulsation through the pedal, or visible rust ridges on the rotor face.
Likely cause
Friction cleans a rotor. When the pads seldom engage hard, surface rust is not scrubbed away and can build into pitting, particularly on cars stored outdoors in damp or salted conditions.
How should it be checked?
Look at the rotor faces through the wheel. Light surface rust that a few firm stops clear is normal; deep pitting or a ridge at the edge is not.
How can you check it yourself?
Look through the wheel spokes at the rotor face on a car that has been standing. Then note whether the first few stops on the test drive sound or feel rough.
The question to ask the shop
What is the rotor thickness against the minimum stamped on it, and is there pitting on the friction surface?