Car Diagnostic Cost: What Does a Diagnostic Fee Include?
Reviewed by Eric Shepherd, ASE-Certified Technician
We have all been there before: you're driving along and suddenly you notice that your car seems a little off. Maybe it's a check engine light, maybe it's making a weird sound, whatever it is, you know it needs to go to a repair shop. Few things can be more frustrating than taking your vehicle to a repair shop after a warning light pops up during your commute on Loop 101 and getting hit with a diagnostic fee and all they do is confirm to you that yes, indeed there is a problem with the vehicle.
We know what you're thinking: Why should you pay when all they are doing is plugging the scanner into the vehicle and it tells them what's wrong and what needs to be replaced. You can have that done at AutoZone for free. While that may sound great to many Arizona drivers, a car diagnostic cost really depends on your vehicle, the shop, and the potential problem that's being diagnosed. It's a little more complicated than just plugging in the scanner and reading any codes.
This is an important distinction to make because the codes can tell a technician where the vehicle detected a problem, but it doesn't necessarily tell you why it happened and what caused it.
So, what are you actually paying for?
What Is a Car Diagnostic Test?
A diagnostic test for your vehicle is the process of figuring out the root cause of the warning light, unusual sound, or issue with your vehicle. It's kind of like when you go to the doctor's office, you're experiencing symptoms and they need to figure out what the cause of those symptoms is. Like your body, your vehicle also provides clues that the technician can use to help narrow down what's going on so they are able to recommend and perform a repair.
Depending on why you brought the vehicle in, diagnosis may include discussing when and how the problem occurs, reproducing the issue, performing a visual inspection, checking diagnostic trouble codes, reviewing live vehicle data, conducting electrical or mechanical tests and test-driving the vehicle.
Each vehicle is different and might not need all the aspects listed of the diagnostic test. Straightforward issues can be identified easily while something like an intermittent electrical issue could take more time to figure out.
How Much Does a Car Diagnostic Cost?
At Gemba Automotive, diagnostic costs can range from $0 to $189, depending on the concern and the type of testing needed. Some concerns may not require a diagnostic fee at all, while others require dedicated technician time, specialized equipment, testing and analysis to determine the root cause.
The exact cost can depend on the vehicle, the symptoms you're experiencing and the complexity of the problem. An intermittent electrical issue on a newer vehicle, for example, may require a very different diagnostic process than a more straightforward problem on an older commuter making the daily trip down I-10 or Loop 202.
If additional diagnostic time is needed beyond the initial evaluation, the shop should discuss that with you before proceeding.
What Does a Mechanic's Diagnostic Fee Actually Pay For?
A mechanic's diagnostic fee mostly pays for the technician's time and expertise that is required to diagnose the issue.
Technician Time
To properly diagnose a problem with your vehicle, it still takes time and work, even if parts haven't been replaced. The technician will most likely need to reproduce the issue, review the data, and perform tests before they can accurately determine what parts need to be repaired.
Knowledge and Experience
Modern vehicles are works of art, combining mechanical systems with electronic components, computers, and so many sensors. It takes a skilled technician to be able to understand how all of it works together and understand what different data points mean so they can decide what to do next.
Professional Diagnostic Equipment
Depending on the issue you are experiencing, technicians might need to use special equipment to diagnose the problem with your car. This can include scan tools, oscilloscopes, smoke machines, pressure gauges, and charging system testers, among other manufacturer-specific equipment.
Technical Information
Because cars are so complex, a technician might need manufacturer service procedures, diagrams and other service bulletins to accurately diagnose the vehicle.
Testing and Verification
When testing and diagnosing, the goal isn't to find a part that might be bad, but rather to gather enough evidence to support the repair being recommended or to support the need for a replacement part. A trouble code is a clue, not a diagnosis. Replacing the part named in the code without testing the system is a little like replacing your refrigerator because the milk went bad. You know there's a problem, but you haven't figured out what actually caused it. That can help prevent a very expensive game of parts darts.
Is a Free Check Engine Light Scan the Same as a Diagnostic Test?
It seems simple and straightforward right? Plug in the machine, get the code and you're off on your way. It's more complicated than that, but the free code scan can still be helpful.
What a Code Scan Does
Modern vehicles are equipped with an OBD-II diagnostic system and port that allow a scan tool to retrieve trouble codes stored in the vehicle's computer. For example, your check engine light just came on and the scanner has received a code that indicates "cylinder 1 misfire detected."
It's great to know that the vehicle's computer has picked up on a misfire, but we don't know what caused the misfire in the first place. That is where diagnosis begins. Instead of just replacing any and all parts associated with a misfire, the technician can narrow down the possibilities, such as a bad spark plug, ignition coil, fuel injector, an issue with the wiring, connector, fuel-delivery problem, compression issue, air/fuel problem or another underlying issue.
The code will identify where the vehicle's computer detected a problem, while diagnosis determines why the problem occurred in the first place.
Why Can't the Scanner Just Tell You Which Part to Replace?
You might be wondering why the scanner can't tell you what part to replace. In our engine misfire example, the scanner is not indicating to replace the cylinder 1 spark plug, it's simply saying that cylinder 1 had a misfire.
This same logic also applies to many sensor-related codes. A code associated with a sensor doesn't automatically prove the sensor itself has failed. It could be the sensor, or it could be damaged wiring, a loose connector, or another component affecting the sensor. Replacing the part that appears in the code description won't always solve the problem.
Why Do Shops Charge for Diagnostics?
Diagnosis is skilled labor. You're not necessarily paying someone to plug a machine into your vehicle; you're paying for the knowledge and experience needed to understand what that information means, determine what should be tested next and identify the actual cause of the problem.
Does the Diagnostic Fee Include the Repair?
Most of the time, diagnosis and repair are two separate services, but the policy will vary depending on who you bring your vehicle to. The diagnostic process will determine what's wrong, while the repair will actually fix what is wrong.
If you are ever unsure, ask the shop how the diagnostic fee works and if you need to agree to repairs before they are done.
Why Might a Car Need More Diagnostic Time?
Some problems can be straightforward while others are not. For this reason, some vehicles might need more diagnostic time than others, like if your car doesn't want to start every third Wednesday and only when it's 112 degrees outside. Arizona heat can also make intermittent problems especially frustrating when an electrical, battery or cooling-system issue only appears after the vehicle has been sitting in a 110-degree parking lot or crawling through rush-hour traffic.
Other issues that can be difficult to diagnose include problems that only happen when the vehicle is hot or cold, intermittent no-start conditions, parasitic battery drains, wiring issues, and symptoms that are hard to duplicate.
Diagnostic Fee vs. Repair Estimate: What's the Difference?
A diagnostic fee pays for the testing and the technician's time to determine what is wrong with your car. A repair estimate comes after the diagnosis is complete and the technician knows what needs to be replaced and approximately how long it will take. The repair estimate typically includes parts, labor, fluids and other materials that could be needed to complete the repair.
When Is Paying for a Diagnostic Test Worth It?
If you have no idea what the problem could be, a professional diagnosis can be super valuable. It can come in handy if your vehicle has the check engine light on, won't start or stalls all the time, the vehicle isn't running right or warning lights keep popping up despite your best efforts. The last thing you want is to keep replacing parts based on guesses only to have the same warning light reappear halfway home on SR-51.
An accurate professional diagnosis can help reduce the risk of paying to replace parts that may not solve the problem.
Frequently Asked Questions About Car Diagnostic Costs
How much does a car diagnostic cost?
The cost for diagnosis depends on the repair shop you are at, the type of problem and vehicle, and the amount of time required to accurately diagnose the issue.
Why do mechanics charge a diagnostic fee?
It takes time, training and professional equipment to accurately diagnose a vehicle problem.
Is a free check engine light scan the same as a diagnostic?
No. A code scan identifies where the vehicle detected a problem, while professional diagnosis determines what caused the problem and what needs to be repaired.
Does the diagnostic fee include repairs?
Diagnosis and repair are generally separate services, but policies vary between repair shops.
Can I diagnose my check engine light for free?
You can—head to the nearest auto parts store for a free scan. It is important to note that retrieving a code isn't necessarily the same as determining the cause.
Schedule Car Diagnostic Testing at Gemba Automotive
A warning light, strange noise or drivability problem doesn't always tell you which part needs to be replaced—and neither does a trouble code.
At Gemba Automotive, our technicians use professional diagnostic testing to investigate the cause of the problem and explain what they find before recommending repairs. That means using the information your vehicle provides as a starting point rather than an automatic parts-replacement list.
If something doesn't feel, sound or run right, schedule a diagnostic appointment at your nearest Gemba Automotive location and let our team help figure out what's actually going on.