Toyota Repair: Excessive Repairs?, excessive repairs, diagnostic fees

Question
Ted,
Please help me try to understand if I am being taken for a ride by local Toyota service center.

Recently, my check engine light came on. Since it was time for my 55k mile service ($110 base charge plus another $200 in 'things' they found wrong.) The bill showed they charged me $80 for diagnostic and said my my gas cap was loose. (I imagined that was reasonable, as I was sure they had to hook up all kinds of wires and plugs to diganose this problem.)

A two days later, it came on again and this time a sensor was bad (at another $80 for diagnostic and $80 for sensor.)

Now the light is on again. I took it to Autozone and saw that it takes 5 minutes to diagnose with the small handheld device and another 5 minutes to look up the fault code in the computer.

I feel ripped off. $80 for 10 mins work seems excessive. And, it seems every time I take my car back, a different sensor comes on.

I have lost confidence. So has my girlfriend. She took her Highlander to the same place for her 60K Mile service ($500 base service, plus another $600 in found things to fix). After she left, the battery light came on. By the time she got it back her alternator was fried and they charged her to replace it, saying their maintence had nothing to do with the failed alternator.

Is all this 'normal' things that go wrong and are these charges and prices reasonable? Are my misgivings misplaced.

Answer
Most dealers have a set price for diagnostic fees, it doesn't matter how long it takes to find the problem, you are paying the dealer for the knowledge and expertise of the service technicians, also I doubt very much that the autozone employee is able to make any kind of recommended repairs based on the diagnostic code other than to tell you to replace the part that the scantool indicates, there is more to it than that, just about anyone can hook up the scantool and retreive a trouble code but you need to know a lot more to actually make a correct diagnosis based on the information and most of the time more testing required wich is included in the diagnostic fee.
I don't know what the problem may have been with the Highlander but something doesn't sound right, I have never seen an alternator do what you said this one did under normal conditions.  Try locating another toyota dealer to patronize.  
You also stated that on he first visit they said the gas cap was loose, if that was the case there should have been three DTCs stored, PO440,441,and 446, not PO171, I'm a little confused about that diagnosis but as I said I would try another dealer and do not blame you at all for having these misgivings about the dealer that did the previous repairs except for the initial labor charge for the diagnostic fees. I have one more question for you, when the Highlander was taken in for the major service at 60K, what was it that they charged you $600 more for "things to fix" just curious.