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Archive for Computer Diagnostics

Why Do Repair Shops Charge Diagnostic Fees?

Today’s vehicles are run by several computers or control modules. To give you an idea of what I am talking about, the engine is managed by an electronic control module, or ECM. These control modules monitor and control the fuel, emissions, temperature, the timing of the engine, braking, starting, charging, transmission shifting and speed. The electrical accessory systems that add luxuries like power windows, door locks, seats, mirrors, heating and air conditioning, are also run by a control module, called a body control module or “BCM”.

When one of these systems in your vehicle starts malfunctioning, a driver is alerted by either the illumination of a warning light on your dash. The vehicle could also start malfunctioning by not starting, a rough idle, running poorly or a loss of power, or the fuel economy level could have changed, or possibly another symptom. 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 it does not tell you 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 that the condition that the vehicle’s computer is seeing. From there a qualified diagnostic technician follows a diagnostic path of pinpoint testing to find the source of the problem and what is causing the condition.

As a comparison a medical doctor has to run tests on patients that are having symptoms to find what is causing a health symptom or condition. The initial exam and tests have a charge associated with them, whether they are blood tests, biopsies, x-rays or scans. Much the same an automotive repair shop too, has a charge associated for that testing time and the expertise of the technician that it takes to perform these tests and form a conclusion based on the information gathered from these tests. To be honest this diagnostic process can be the most complicated part of vehicle repair. The technician who is delegated this task is a specialist in vehicle computer diagnostics. These technicians, constantly continue to further their education, training and upgrading of their tools and equipment, since the systems on vehicles are constantly evolving and changing.

So don’t be surprised when you are quoted a diagnostic fee next time your vehicle acts up or a warning light comes on in your dash. In reality it is less expensive to pay for a proper diagnosis then it is to replace parts based on what might be failing, or what is most commonly replaced or the hunch factor. Steve and Karen Johnston are owners of All About Automotive in Historic Downtown Gresham. If you have questions or comments, call them at 503-465-2926 or email them at Steve and Karen Johnston are owners of All About Automotive, providing auto repair and auto maintenance in Historic Downtown Gresham. If you have questions or comments, call them at 503-465-2926 or email them at, you can also visit our website at

To schedule an appointment for service or repair, call 503-465.2926.

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