Some bigger shops will charge you for diagnostics but deduct that cost from a repair if you have them do it...others want you to pay the full cost of both.
I had a check engine light come on in the Jetta. The local mechanic shop that's done most of the repairs on my European cars wanted to charge $97 to diagnose the problem, then another cost for the repair, depending on what it was.
The VW dealership wanted $120 to diagnose the problem, but would deduct that from the cost of the repair.
I borrowed a code reading tool from my neighbor, (never knew he had one) hooked it up, read the codes, found out it wasn't anything serious, cleared the code with the tool...and it's never come back on. Once upon a time, I did all my own auto repairs, but since I got hurt, I have to have all that simple stuff done in a shop...it really sucks having to pay someone to do things I know HOW to do...but physically CAN'T do anymore.