The Trading Standards Institute and Motor Codes are now partners, taking over from the Office of Fair Trading to provide a Government-backed code of practice for garages.
In a survey looking at motorists' experiences of getting their cars repaired, the AA found that 44% of respondents thought the cost had been higher than expected, while 22% believed items that had been fitted or replaced unnecessarily.
Garages that join Motor Codes are allowed to use Motor Codes' branding and display a Trading Standards-approved logo.
The code calls for more clarity, honest services and for there to be a straightforward complaints procedure should something go wrong.
So far more 7500 garages have signed up to the scheme with 2000 of those being independent garages.
Customers can rate their experience of garages by logging on to the Motor Codes website. Here, all member garages are rated and reviewed with more than 115,000 reviews currently recorded on the site.
All reviews are posted online without editing by Motor Codes. Negative reviews are allowed and should there be a string of complaints, Motor Codes will start an investigation procedure to check whether a garage can remain a member. A handful of garages have lost accreditation since the scheme started and so far Motor Codes garages have a customer satisfaction rating of 96%.
Motorists also benefit from a free advice service to help sort out complaints before they escalate. Garages also benefit from a free advice service and get training to help meet the guidelines.
Chris Mason of Motor Codes said: '90% of complaints made to the Motor Codes advice line are sorted out through improving communication between the customer and the garage.'
To rate your garage or find an approved garage go to the Motor Codes website.