Understanding some truths about the word, diagnostic.
From an auto repair technician's view, it simply means to figure out what's wrong with the vehicle, so they can give an accurate repair estimate.
For example, If the power window in your car does not work. The auto tech must perform testing to see if its the switch, the motor, the hardware or no power from fuse box. The checks take time to analyze, to keep the auto tech going in the right direction of isolating failure point. Power windows don't all fail the same way, just as all humans don't all fail the same way. The technician must go through tests and analyze the results before prescribing a fix for you.
Another example, a squeak from the suspension... It may be easy enough to just push on the car, and duplicate the noise. But there is so many moving parts, like ball joints, shocks, bushings, bearings and other components. The real way to isolate the noise... Is with electronic listening equiptment that is placed on each joint or point that includes moving parts. This proves out the spot of noise, with no guesswork. But does in fact take time and investment into the tooling. And needs to be charged accordingly.
" A simple electrical problem." Actually, electricity is as simple as the universe and everything in it. How simple is that? :) The simplicity comes from not understanding it.... You cannot visually see electrical flow or pressure, and you for sure cannot see digital signals on network communication lines in a modern car without a proper scan tool. You have to measure electricity to analyze what its doing. Watching a light bulb illuminate is not seeing electron movement, your just witnessing the product of it. The person that understands electrical theory, knows there is nothing simple about it.
Imagine, your watching a water wheel, like at an old mill. The water is moving it. And a certain amount of water is pushing the wheel at a particular speed. Ok, a speed sensor(like engine speed or wheel speed) is similar but on the other hand is using magnetic invisible lines in space to move it. You cannot see the invisible lines like you see the water. You can only see and measure it with tuned instruments and meters to see exactly how much or how fast the water is traveling over the water wheel. Then, the person using the instruments must also be able to analyze the results to see how it compares with desired data from engineering and design.
Another diagnostic dilemma... It seems from many people's view, diagnostic means the mechanic simply plugs in a computer and the magic box tells the mechanic all the car's problems in a few minutes. Prescribing a fix based only on trouble codes read from a code reader, is about 75% guesswork. The code read is only a direction to take, to the next step. There are many reasons why the process seems over simplified and should not require a cost. To start, many mechanics don't value their time during diagnostic, because they don't actually know the theory of operation of the system they are testing. So they offer this service free, or at reduced rates because they don't understand what they are testing or even have the correct tools to test with. They rely on past experiences, common failure patterns and seat of the pants guesses to guide them to an estimate of repairs(which result in those complaints of "I paid $$$ but it still does the same thing") This greatly devalues the true professional's investment into knowledge and tooling. Another reason why this service seems to have no value, is diagnostics are usually used as a loss leader. Its very bad for a shop or person to have signage up or a business model that says "free diagnostic." As it usually takes the most experienced, most knowledgeable and usually the eldest person in the shop to perform diagnostics properly, yet the shop does not charge accordingly for this highly paid professional. Well, actually, many shops don't even have this highly paid professional that we all think of. That's a story for another time...
There seems to be no value in a diagnostic... The simple fact is. Time is money. If an auto repair technician is diagnosing and analyzing test results, it is costing someone money. Either himself, the shop, or the customer. The term, "free diagnostic" does not belong in the automotive industry, in my opinion. The veterinarian always charges for a diagnostic, even though he's just petting the dog, looking into its mouth, asking you questions and such. We expect to pay him for his analysis. The auto technician is in the same game. Maybe there is not much value if you are not witnessing the analysis. But believe me, its going on. No one just walks up to the car and waves the magic wand of repair, to make it all better. A doctor or dentist uses equipment, along with critical thinking skills to help determine causes of the complaint. The auto mechanic uses equipment, with critical thinking skills to locate the cause of the complaint also. To locate, cause and effect scenareos.
A free code pull... Is not a diagnostic by any means. Parts stores and some people, supply this service, to sell parts. They do not guarantee anything about the recommendation. Its the same as "take two aspirin and call me in the morning."