Why Do Automotive Repair Shops Charge Diagnosis Fees?

Why Do Automotive Repair Shops Charge Diagnosis Fees?

Why Do Automotive Repair Shops Charge for Diagnosis  – Diagnostic Fees?

Automotive repair shops need to charge diagnostic fees because modern vehicles are extremely complex computer controlled machines. It requires the labor time of a highly trained and experienced technician to perform tests and use expensive equipment to competently perform a diagnostic. The old days of looking under the hood of a carbureted car and identifying exactly what the problem is, are gone. We are now light years ahead in technology and complexity. The diagnostic process is complex and must be thorough.

Most vehicles produced since the mid 1980’s are run by at least one, usually several computers or control modules. Today’s most advanced modern cars (Audi, BMW, Ferrari, Porsche, Lexus, Mercedes-Benz, Mini, Fiat, Maserati, and Nissan) may have up to 40 or 60 or more computers that communicate and share data on a Fiber Optic Network (known as CAN). The engine is managed by an electronic control module, or ECM, ( also known as PCM or DME) . These control modules monitor and control the fuel, emissions, temperature, the timing of the engine, braking, starting, charging, transmission shifting and speed. Automatic Transmissions are controlled by a transmission control module or TCM. The electrical accessory systems that add luxuries like power windows, door locks, seats, mirrors, heating and air conditioning, multimedia entertainment, self parking, auto cruise control, are also run by a several control modules, each called a body control modules or “BCM”.

When one of these systems in your vehicle starts malfunctioning, a driver is alerted by either the illumination of a check engine light or another notification. If your vehicle won’t start, or the fuel economy and performance level has changed, or possibly another symptom, it takes time to investigate and research the cause of the issue. In order to properly diagnose what is going on with the vehicle and conclude what the proper repair would be, it takes knowledge, equipment and time for the automotive technician to run the needed tests. Unfortunately, when you tap into the vehicle’s ECM, in most cases it does not tell you exactly what is wrong. In fact, the ECM makes adjustments and changes to compensate for the symptom that it is seeing, so the vehicle will still operate as close to normal as possible. The diagnostic process starts with retrieving the code or codes from the ECM.  These codes give you the circuit or circuits that are affected, and what the vehicle’s computer is seeing. This gets confusing for the public, “Do-it-Yourselfer” (DIY), or untrained mechanic because these circuits are often named after the sensor from which they are connected. Often the failure is caused upstream of the sensor and the computer is reporting that it is receiving irregular signals from that particular sensor. For example, nine times out of ten, a code for an oxygen sensor, is typically not due to the failure of the oxygen sensor. It is related to another problem that the computer has detected from oxygen sensor. It is the job of a qualified diagnostic technician to follow a diagnostic path of pinpoint testing to find the source of the problem.

A doctor charges to examine and run tests on patients that are having symptoms to find the answer. Just like a doctor, an automotive repair shop, needs to charge for that testing time. The diagnostic process can be the most complicated part of vehicle repair. It takes a specialized diagnostic technician to perform the tests on the vehicle. These technicians are the most expensive mechanics in the automotive field. They constantly have to continue to further their education, training and upgrading of their tools and equipment, as the systems on vehicles are constantly evolving and changing.

Don’t be surprised when you are quoted a diagnostic fee next time your vehicle acts up. In the end it really is less expensive to pay for a proper diagnosis, than it is to replace parts based on the ‘hunch’ factor.

The cost to fix a vehicle depends on:

  • What is wrong with the vehicle.
  • The repair facility you take your vehicle to for repairs (or whether you try to fix it yourself).
  • The prevailing labor rates in your area and overhead cost to run the business.
  • The year, make and model of your vehicle (luxury imports are always more expensive to fix!).
  • The availability of parts for your vehicle (are the parts only available from a new car dealer or can they be purchased from a local auto parts store?)

In most cases, you will pay for what you get. In other words, the better and more specialized the repair shop, the better and more trained its staff will be, and the more accurate and more expensive the diagnostic equipment will be.  In most cases, the best independent specialty repair shops, staff technicians with factory training and use dealership level diagnostic equipment. This allows them to more accurately and quickly diagnose a problem in most cases. Ultimately the diagnostic time and the overall repair cost will be less than spending your money with a less capable shop that will throw more parts and time at a problem trying to guess what is wrong or make mistakes that may cost you more money in repairs down the road.

Phone: 408-831-3730


Sprint Motorsports celebrates the glory of the automobile in all its forms. We take pride in caring for our customers, and are invigorated by the opportunity to provide competent and comprehensive automotive repair services. We strive to be the leading repair, tuning, and race facility in San Jose and adjacent areas while providing you personalized, detailed, and friendly service. Our relationships are built on trust, communication, integrity, and commitment to our purpose; to be the best auto repair shop we can be.

To schedule an appointment for auto repair, major or minor services, please contact service@sprint-motorsports.com or 408-831-3730. We welcome you to stop by our auto repair shop located at 2099 S 10th Street, Unit 40, San Jose, Ca 95112.  If you have any questions about your car’s repair needs, performance, or maintenance, ask our friendly and expert staff for assistance.