What's to figure? IMO, fair for a straight forward nuts and bolts type job is flat rate X shop rate + parts. For the kind of job you're talking about, generally it's your time spent X your shop rate + parts. That's whats fair. The tools are part of the shop rate spread across all the jobs you do as well as the cost of the building, electricity ect. The question is when is a car not worth fixing? IMO, the '97 probe became scrap iron when a junk yard engine out of a '95 was considered an improvement. Kudos to you for being able to figure it out. You did so quite quickly imo. I don't even think it would be unreasonable to charge 2x the time you spent on it in this case. You're not being paid for switching a couple plugs. You're being paid for knowing which plugs to switch. If it were me (as a customer) I'd be thrilled I found someone who could fix the thing. jmo

Well John, you've done it again - figured out a mysterious problem that was hidden in plain view. Unfortunately, the $40,000 worth of diagnostic equipment could not positively identify the problem; It took a good diagnsotician to do that.

Who'd thought: crossed wires. Did those wires have the same color, too? This would be funny except for the pain it caused.

With the abundance of differently shaped connectors under the hood, one would think that two connectors in proximity of each other would have been shape-keyed to prevent crossing the connections. Design oversight?

Since you're soliciting opinions, here's mine.
Your diagnostic tester is not a "typical" shop tool so It should not be lumped in with general shop overhead or "the cost of doing business". I think that a charge for the use of the equipment is both fair and in order here.

In addition to the inital cost of a machine like this there is maintenance/software upgrade/ service contracts/ etc.
You should develop a rate for usage of the device and include it on your invoices (in case someone wants a detailed breakdown). Something like $200/use I don't feel is unreasonable in addition to your time. FWIW, I can understand the justification for the old "joke":

shop labor = $x/hr
unless you fix it first, then
shop labor = $2x/hr

john_g I wish you were near me. Based on your posts, I'd bring my car in for sure.

Thanks guys, I appreciate the responses. It's fun being able to write about these things, but in many ways it's "just another day at the office". This diagnostic is going to cost the customer the two hours I put into it at my regular diagnostic rate of 84.77/hr. In other words less than $200. He came by the shop this morning, and when I told him it was fixed and what was wrong. you should have seen the look on his face, PRICELESS!! He has been fighting this problem for a year! By the time he showed up I had already taken this on a road test that was long enough to run the EGR monitor which had passed, confirming the car is fixed. He asked me to go ahead and do the state inspection on it, and also fix the shifter interlock system.

The question still remains though, trying to figure out what is "fair". In almost every way, I can't afford to keep doing work at this level, and keep myself tooled, schooled and up to date without charging a lot more than I did. But if I charge more would I get any work at all? Most of the time I don't even get a chance at doing the work as it is. We lose so many potential jobs right at the phone estimate because there is always going to be someone cheaper. Cheaper does not mean better, it never did.

"I have a little over an hour's time in the shop invested. I have a little over an hour here at home studying this system and looking for every scrap of information I could find when I found that."

"This diagnostic is going to cost the customer the two hours I put into it"

Sounds like you put in 2.5 hours, stop selling yourself short. LOL

In almost every way, I can't afford to keep doing work at this level, and keep myself tooled, schooled and up to date without charging a lot more than I did. But if I charge more would I get any work at all? Most of the time I don't even get a chance at doing the work as it is. We lose so many potential jobs right at the phone estimate because there is always going to be someone cheaper. Cheaper does not mean better, it never did.

Ask yourself this: aside from the "free help" that exchanged the engine, how much did the owner of this car spend in other shops trying to fix this problem? Way more than $200, I'll bet. And they got paid even though they didn't fix the problem. And yet you are the one with the experience and the knowhow and the tools to actually get it working again. How much is that worth? Why is it that two people can pick up the same paint and brushes and canvas and yet one of them can sell everything he touches and the other cannot? Why do people pay $$$ for blue jeans when they can buy 'em for $10 at Wally World or Tarjhay? It's the art behind it. You have an art, too, and, really, coming to you probably costs less in the long run than going to some cheap hack who doesn't know a from e.

Maybe that's a marketing thing. Maybe the shops referring to you need to endorse you publicly to the customers ("Yeah, John's not the cheapest guy in town, but he is the best and if John can't fix it, no one can."). Maybe it's doing more referral work from more dealerships/a wider area. Maybe you need to branch out into some other aspect of car care that is more bread-and-butter, like fast oil changes or installing aftermarket accessories, so you have a broader customer base over which to amortize your costs.

You're d**n good at these diagnostics and you seem to enjoy it. Like sdello said, don't sell yourself short. You do what no one else in your area does. People almost always will ante up for the good stuff. Make sure people know what they're getting from you and that they can't find it just anywhere.

John, you are certianly entitled to charge a portion for your equipment, although you did not use it to make the repair, using it enabled you to eliminate enough to read and get the proper info. Plus you are entitled to a fee for using some damn hard learned diagnostic knowledge, I don,t think any fair minded person would quibble over this. Thanks for a very interesting post

Footnote.

This customer has another car that the check engine light came on. He stopped and asked me about it, and we set an appointment for it. He didn't show up. Word has it he got it done cheaper than he thought we could, or would do it.

(I know where it did go)....