Fault finding, before anything gets replaced
A code reader tells you which circuit is complaining. It does not tell you which part has failed, and a swapped part that was fine is money you never get back. What you want is somebody who reads the code and then goes and checks what it is pointing at.
We plug in, read the fault codes, then test the thing the codes accuse before anything is ordered. Sometimes the sensor really has failed. More often the sensor is telling the truth about something further up the loom.
Intermittent faults are the ones garages hand back. If yours only does it cold, only does it in the wet, or only does it on the way home, say so on the phone, because that is usually the half of the diagnosis that gets left out.
from the start to diagnosising what was wrong with my car to fixing it