We get a lot of questions from customers that ask why we, and any repair shops, charge for diagnostics. Its a fair question but the answer is anything but simple. It has a lot to do with the differences in modern cars compared to what they used to be. It also has to do with a lot of misinformation out there and the difference between a cheap scan tools you can buy online and ones used in a professional shop. Finally there is a big issue of the difference between diagnosis and just reading codes and throwing parts at the issue.
A little comparison of cars from the 1950's (or even into the 80's for some brands) helps to get us started and I will mainly focus on the engine in this example for sake of brevity and clarity. When cars started becoming a product that every household wanted its important to understand time and context. In the 1950's particularly in North America it was a period after the war, production of cars was ramping up, many of the lessons learned from the military were working their way into the automotive industry. As an example even in motor oils see a previous post of some of the wartime discoveries that were creating longer lasting cars. The new 'cold war' was on and many people wanted to work in the city but live outside in the suburbs or even a different town. The new interstates and roadways across North America gave people the freedom to do just that.
In terms of context, pollution, fuel mileage, looks over safety and other safety features were not really considered early on. A typical engine needed oil, a spark from a distributor and fuel from a mechanical pump. Transmissions were generally 3 speed automatics or a 4 speed manual. The most sophisticated electronics were within the radio, and those were vacuum tubes. Brakes were drum brakes (generally) and ABS or Traction Control weren't phrases that had even entered the lexicon of automobile manufacturers. Every connection in the car except for some rudimentary electronics was a mechanical system and a mechanical connection.
As the years passed and the auto took off in sales people wanted more. By the 1970's crippling fuel costs, a demand for more safety and better mileage and the advent of the first rudimentary computers drove intense decades of development and with it more complexity. As customers demanded more from a car, from safety to better fuel mileage cars began to move away from mechanical systems to ones that involved more computers, monitoring systems, and eventually they became interrelated. Standard diagnostic codes and ODB II (On Board Diagnostics) came together to give some standards but the way systems and other computers relayed information can be very proprietary. Some modern vehicles communicate via fibre optics within the vehicle between modules while others use shielded wires, proprietary communications standards etc.
Have engines become that much more complex?
We are a European shop and its obvious we have a love for all things Porsche so I will draw on two engines from Porsche from two different eras. If we look at an early air cooled Porsche engine from a 911 from the 1960s its a beautifully engineered motor just under two litres. An air cooled flat six mated to a 5 speed manual '901' transmission. The lightweight car had about 130 HP. Compare that to a modern day Porsche engine of similar displacement like a 2021 base model Cayman. It also has a two litre (water cooled) turbocharged 4 cylinder engine but produces 300 HP. None of that would be possible without complex system management computers for fuel injection, 02 sensors, knock sensors, coolant, tires, ABS, traction control, air bags, power windows, remote start, remote door locks, timing sensors, boost sensors, wheel speed, transmission control and on and on. The greater the number of parts of sophistication of the engine means incredible performance, but only if all systems and sensors function perfectly. When one part fails it may look like something else failed instead based on just looking at the fault code alone.
Thats all good but why can't you just buy one of those scan tools online for a few hundred bucks?
Its a good question, and the answer also lies in the difference between reading a fault code and diagnosis. One is a simple task, and the other is far more complex. Scan tools and other electronics are cheap and readily available, you can pick one up for under a hundred dollars. They will plug into your ODB II port and read fault codes. We often get asked if what we do now with modern cars is just read a fault code and replace a part, in fact that is what lesser shops do. The challenge is that reading a code likely wont help in most situations. It may point out that your 02 sensor is reading low and that may lead down a rabbit hole chasing parts that aren't the issue - they just appear as an issue down the line. On top of that, although fault codes may be somewhat standardized, every single vehicle has different arrangements of computers that communicate with each other on everything from fiber optics to proprietary data systems. No ebay scan tool can make up for years of training in automotive systems and diagnostics.
So what am I paying for?
A good shop has the right tools for the job, and each brand often has a specialized scanning tool that is used on a particular brand of cars. Even cars under the same umbrella of ownership needs different tools for different cars. If you take VW Aktiengesellschaft there is VW, Porsche, Bugatti, Lamborghini, SEAT, MAN, Bentley, Audi etc - 12 brands in all and each needs a scan tool that can go much deeper than one bought at an auto parts store.
Are the scan tools you use really that expensive/good
As an example for one brand - Lamborghini, a used scan tool (yes used) is about $19,000 CAD if you could find one. We have scan tools for all the brands that we service, plus license fees, access to the latest technical bulletins, training and techniques. We pay subscription fees for the latest software updates and most recent information. On top of that we have the training in diagnosis of these complex systems. We have scan tools specific to each brand we service or we have access to similar but very sophisticated computers but they really give us a look at 'flags' the computers throw for faults, they also give us a much deeper look than a cheap scan tool can.
I still don't fully understand - give me a better example
Sometimes a better example is thinking about it differently. When you see a doctor for a general complaint they draw on years of training and a host of diagnostic equipment that assists in diagnosis but doesn't do the diagnosis for them. If you come in with a specific complaint like being tired it might be a simple thing like a need for more sleep, or it could be something more complex like an underlying neurological issue. The experience, expertise and tools are why you go there. Its the skill and experience and access to the latest medical information and training that you are utilizing. You don't (or shouldn't) get your medical advice from Google - I did once and its turns out I was just thirsty, which is good as Google said I may have rabies (I don't) . Silly example aside, its a good one as its about making a diagnosis with more than just a description. For us its about finding all of the facts to support a diagnosis and a conclusion for your car.
Is it fair to compare our technicians to a doctor? Obviously not in all things but in terms of a diagnostic process yes. Neither profession relies on a guess or a piece of diagnostic equipment bought from an auto parts site on the internet. You would likely be a little taken aback if your health care provider showed you and xray machine they bought on ebay, or said they did their medical degree virtually and didn't think the practical experience of hands on training was worth it.
Its no different than that in a modern shop. Sometimes the problem is really a simple 02 sensor replacement and sometimes the problem is something more than that in a complex web of systems. Even the older cars with simple carbs and vacuum lines require a holistic look at the overall car, and not just a focus on fixing the symptom.
What you are paying for in a modern shop is training and experience in diagnosis of a rolling complex computerized systems that also happen to be an automobile. A scan tool is part of the diagnosis and its a very expensive and specialized piece of equipment that is only part of the overall tracking down of the issue. If your shop tells you they are chasing down fault codes and replacing parts as the codes tell them too, find a shop that knows the difference between code chasing and diagnostics. And don't ask them if they think you have rabies.