How it works
Four steps, and you can stop after any of them. Nothing here obliges you to book anything.
Read the fault
The reader plugs into the socket every car built since 2001 already has, usually just under the steering wheel. Your phone picks up what the car reports about itself.
Understand it
You get the fault explained in words you can repeat to a mechanic, with the parts usually involved and roughly how long the work takes.
Ask for prices
Send the job to garages near you and see what they quote. You choose who to talk to, and you are never passed on to anyone you did not pick.
Decide
Book the garage you want, take the information to your own mechanic, or do nothing at all. The answer is yours either way.
When the answer is stop driving
Brakes, steering, airbags, high-voltage systems and fuel leaks are treated differently. If your fault falls into one of those, you are told to stop and arrange recovery, before you are shown anything about prices or garages.
Why you will not see a made-up price
A repair price you cannot trace back to a real garage is a guess, and a confident guess is exactly what leaves people out of pocket. You are shown what garages near you actually quoted, or you are shown no figure at all.