Never underestimate the power of the government (or sometimes, the stupidity of it).
Do you have an OBD II port in your car? Yep, and you can buy a reader for $20 on eBay, a rather good one costs a bit more, and there are readers in the several hundred dollar region for specific cars (MB, BMW, etc.) Even Harbor Freight sells them (but no more coupons, I guess Comrade Xi needs the money . . . )
OBD II was mandated by the Feds about 25 or 30 years ago (I had a 1990 Audi with OBD-I, it would blink out a few codes), OBD II works very nicely, and I have a brand-specific reader for my MB. It cost something like $399, but it has saved me many multiples of its price. Plug it in, it reads EVERYTHING and saves hours and hours of diagnostic time (the dealer gets $150/hr) plus running the car back and forth, alternate transportation and so on. In fact, I bought it used from someone who wrecked his car, I paid him a whopping $50 - and it saved me ten times that the first time I plugged it in.
So here I am in the middle of a field, my tractor stops and I don't know why. Has fuel, no nasty noises, nothing obviously busted, it just won't run. Plan A - load it onto a trailer, take it to the dealer, pay $$$$ for diagnostics, pay $$$$$$$ to have the parts installed, put it back on the trailer, take it back to the field and go back to work. Total time a couple of days and boo-coo dollars.
Plan B - plug in the $300 diagnostics box right there in the middle of the field, it tells me I need part number 34-3456B, which is a left handed widget frammis solenoid and my dealer has one in stock right now. Go get it (leaving the tractor where it is), bring it back, install it myself in eight minutes, back to work the same day.
I like Plan B, it is worth paying the $300 for the magic box because it gets me up and running FAR faster and for FAR less money and with FAR less hassle than Plan A.
Vehicles of all kinds nowadays are much more complex than in the old days. Part of it is they are more capable, and part of it is various regulations. Diagnostics can get very expensive with all these interrelated systems, which is why OBD II was mandated in the first place - there was no confidence that repairs would be done to satisfy emissions requirements given the complexity of the systems.
The only constant is change . . . if we are lucky, this will be for the better. Captive service and captive parts are definitely no bargain for us. The FTC is getting ready to break that barrier so we can fix our own stuff again.
Best Regards,
Mike/Florida