Before I had some of the diagnostic equipment myself (mainly a scan tool with live data), and gained experience while I was in school, I had several ‘friends’ take their own cars to a shop and have it diagnosed. They would then call me and tell me the diagnosis, how much the quote was, and if I could do it for cheaper. Most of the time I could/would do it. If you take your car to (insert repair shop) and have to pay $90 to have it diagnosed because they charge a flat rate hour, and decide you can do the job yourself, then do it in my opinion. Personally, now that I am near the end of my classes, diagnostics have become my favorite part of working on a car, as I love putting the pieces of the puzzle together. But if I were to run across something I absolutely could not figure out, then I wouldn’t feel bad about doing this. The guy still got paid, and the shop still made money.
I guess the only thing I would feel guilty about would be if the tech had to obviously do more than an hour’s worth of work to diagnose a problem and then only charged for one hour. If that were to happen, which I find unlikely, I might ask to talk to the tech and slip him a twenty dollar bill, especially if he had to put stuff back together for the car to be driven away.
On the flipside of that coin though, before I started school, I had a ’95 Taurus that was running like dog crap, and I could NOT figure out the deal. I took it to a shop, and got a ‘diagnosis’. The quote basically said that a bad motor mount had caused the MAF to unclamp from the airtube or some crap. They wanted $500 to replace the motor mount and fix the ‘air leak’. I went out and looked at the car, and found that the bottom side of the airtube had slipped off the throttle body. I pulled a dime out of my pocket, and used it as a makeshift screwdriver, loosened the clamp, and re-attatched the piping. I had thought I had done a thorough visual inspection, but obviously not good enough. So, they will make their money back on some other sucker. That guy didn’t get a tip.
Just to make this ‘short’ story longer, there were no other cars in the lot, and nothing in the bays. They were obviously looking to make up for lack of other business. Since then, I only go to this spot for tires, because they offer decent cheap ones. It was a chain called Grismer’s. I hate dropping names like that, but I have heard so many horror stories from folks about them, I can’t help it this time.