Why should I pay for a professional diagnosis?

The Importance of Professional Diagnosis

FREE Diagnostic Checks

As a professional technician at Mobile Engine Medics, I often encounter customers who have already tried to diagnose their own car issues with the help of a free service. One example would be a “free diagnostic check” offered by auto parts stores. While these services may seem helpful, they often only provide a fault code and a guess of what to replace with no guarantee of accuracy or resolution. 

Code Confusion

One common issue I often come across is the P0171 “system too lean” code. This fault code can be generated by a great many potential root causes.  The engine computer has determined that it is having to overcompensate by adding fuel to correct for a lean condition. It uses the data received by the oxygen sensors to determine this. While the fault code is a great starting point, a fault code printout from a free service is not a diagnosis- it’s a guess. You should not simply replace your oxygen sensor because this fault code is present for one or more engine banks.

Unpeeling the Onion

We have a fault code, great! Although fault codes aren’t always present with a performance complaint, in this instance, this is where professional diagnosis starts. Unlike what I call “guess-nostics”, or free fault code readings, a professional diagnosis involves a thorough examination of the car’s systems and components. I rely on my expertise and advanced diagnostic tools to identify the root cause of the fault code and provide an accurate diagnosis. 

The Fault in our Faults

The fault code is only the starting point for this process. We condemn only the failed parts and avoid replacing unnecessary and costly additional parts that get you no closer to resolution. This also avoids repeated part failures by addressing the underlying issues. The potential exists for the oxygen sensor to be malfunctioning, but if it is, what caused it to malfunction? What if you only had a vacuum leak or an exhaust leak? The same fault code is likely to occur, and in this instance, circumventing the diagnostic process and hiring us to replace 2 oxygen sensors you purchased simply because the free service said “try replacing this” will have a disappointing result. Not only will you have incurred the expense of parts and labor to replace 2 parts that weren’t damaged, but your check engine light is still on, and now you still need a diagnostic.

Top Hose on the Left

This same principle applies to other aspects. I recently encountered a customer who needed their power steering hose replaced due to a leak. However, there typically are at least four different hoses in this system.  The customer was unsure which one needed to be replaced. 

A part that has failed and is leaking, covers parts in fluid that aren’t leaking. By purchasing a professional diagnosis, I am able to pinpoint the exact hose that needs to be replaced – rather than, “I think it’s the top one to the left.” When someone approaches me in this manner asking for help, it is very difficult to be accurate. 

Quotes VS Estimates

It’s important to note that there is a difference between an estimate and a quote. A quote provides an exact cost, whereas an estimate is a rough approximation. As a professional technician, I provide my customers with estimates that reflect the cost of parts and labor needed to fix their vehicle. Although an accurate estimate is possible for a repair, what a customer truly is asking for is an estimate for a meaningful resolution, and that can be difficult, if not impossible without first having a diagnostic performed. 

Why this is Important

It’s not just about revenue generation for me. I believe in providing a high-quality service that delivers results. That’s how we develop a reputation of integrity, maintain lifelong customer satisfaction, and continue to change the experience of what automotive service should be. 

Save Money, Save Time, Call Me First

In conclusion, while we can replace any part that you hire us to replace, we will almost never recommend to our customers to replace a part based solely on a free diagnostic check. Professional diagnosis is crucial for accurate and effective car repairs. While free services like fault code readings may seem helpful, they often do more harm than good and perpetuate the normalization of changing unnecessary parts until you “fix” a problem. 

At Mobile Engine Medics, we save our customers money, time, and headaches over the life of their vehicle. So, if you’re experiencing car troubles, don’t hesitate to reach out to a professional technician – we’re here to help.

Zachary Bernet
Zachary Bernet

ASE Master Technician
ASE Advanced Level Specialist
Master & Diamond Certified Mechanic

(916) 256-5962


65 Vintage Court
Clayton, NC 27520
United States

[email protected]