Because diagnosing a problem isn’t just hooking up a scanner and reading the fault code if a code is even flagged by the ECU.
Why is it ok for doctors to charge for medical tests, x rays etc, but a mechanic should somehow spend hours finding a problem for free ?
Some diagnostic tests can take considerable time and expensive tools . A lot of diagnostic tests and procedures take a lot longer than the actual fix.
It is not uncommon to chase a bad ground that works intermittently for hours and hours and the fix takes less than 5 minutes and a new 50 cent connector.
If a technician spends hours trying to get to the bottom of a difficult to find, intermittent electrical issue and the car is out of warranty who should foot the bill ?
It is not the fault of the dealership that the car broke down. The manufacturer sold you the car with a warranty clearly stated on the contract. You knew when you bought the car that the warranty will not last forever and you should also know that a car is a machine and machines break down over time.
Many people think that reading a fault code that illuminates the “check engine light “ is the end of the diagnosis as the computer knows what the problem is and so any trained monkey can go in there and replace whatever sensor was flagged.
This could not be further from the truth.
A fault code flags a particular sensor or a system that spews out information that the computer deems out of range . The technician must figure out if indeed it is just the sensor, the wiring to the sensor or the component that that sensor monitors or a glitch in the computer . Some sensors are super expensive like some air fuel ratio sensors , previously called oxygen sensors or MAF sensors and can cost hundreds of dollars .
If the sensor is relatively cheap and we know it is a common failure we will call you and ask you if it is ok to throw in the senor without diagnosing further even though it might not fix the issue. The reason being is that due to a high failure rate of that specific sensor you will need one eventually and chances are high that replacing it will fix the issue. If it doesn’t then we will start the diagnosis . But we cannot do that with a sensor that costs hundreds of dollars .
Modern cars have very complex systems and dozens of modules that communicate with each other . Everything is interconnected and one bad wire , one bad connection and the technician is faced with hours upon hours of test time .
The important thing here is to have your car tested at a place that is familiar with your make of car and has the necessary tools and training to successfully find and repair the problem . We turn many customers away when they show up with a vehicle we are not familiar with . Carss have become far too complex for a single shop to be properly trained to work on anything .
Again, to use the medical profession as an example, you would not make an appointment with a proctologist if you have an ear ache .