Diagnostic Trouble Code (DTC) Troubleshooting Tips for the DIYer

If you’re like most DIYers, you probably have a scan tool or code reader that you use to check for diagnostic trouble codes (DTCs) when your car’s check engine light illuminates. Retrieving the codes is easy, but sometimes diagnosing them isn’t so simple.

As a backyard mechanic, you’ll eventually be confronted by a code that leaves you baffled. Fortunately, there are some tips that you can use to diagnose these challenging DTCs.

Four Essential DTC Troubleshooting Tips for DIYers

Is your car’s check engine light on? Here are a few tips that will give you a better shot at diagnosing the corresponding codes.

Recognize that a Code is Not a Diagnosis

First, it’s important to point out that codes do not tell you exactly what’s wrong with your vehicle. Instead, DTCs merely serve as a starting point for further troubleshooting.

For example, if your car logs code P0131, which stands for “O2 Sensor Circuit Low Voltage Bank 1 Sensor 1”, that doesn’t necessarily mean there’s a bad oxygen sensor. A faulty O2 sensor is just one of many possible causes for code P0131. The root of the problem could be anything from a wiring issue to a lean running engine.

That’s why it’s important to read the service information (as we’ll discuss below) and perform a thorough diagnosis when troubleshooting codes.

Look Up the Official Service Information in a Repair Database

Another crucial step is to look up the official service information for your vehicle before you begin the diagnostic process. In the past, official service information was only available to repair shops and dealerships, but now it’s also accessible to DIYers through online repair databases.

These databases, such as ALLDATA DIY and Mitchell 1 DIY, give you access to vital DTC troubleshooting information, including OEM code definitions, diagnostic flowcharts, wiring diagrams, and more.

Obtaining access to service information is also affordable. DIYers can purchase single-vehicle subscriptions to both ALLDATA DIY and Mitchell 1 DIY for a reasonable fee. Check out our article on repair manuals and repair databases to learn more.

Don’t Believe Everything You Read (or Watch) Online

Sure, there’s a lot of good DTC troubleshooting information online—but there’s also a lot of bad information. Online resources, such as FaceBook groups and YouTube videos, are best used to supplement service information derived from a repair database. Blindly following online repair advice can lead you down an expensive and time-consuming rabbit hole.

While there might be instances where an online search yields a “silver bullet fix” for your particular vehicle and code, that’s not usually the case. Even if you’re getting your information from a reputable source, what fixed a code on one car might not fix it on yours. 

After all, if diagnosing cars was as easy as performing a Google search, there would be little need for professional mechanics. Take what you read and see online with a grain of salt, and use your brain to diagnose your particular problem.

Understand the Limitations of Your Scanner or Code Reader

Almost every DIYer has a scanner or code reader, but unfortunately, some don’t know the limitations of their particular tool. Code readers can usually only read and clear codes in the engine and transmission computers. Scanners can retrieve codes and also display live data, but not all scanners are created equal.

There are two primary types of scanners: generic OBDII and OEM-enhanced. Usually, generic scanners can only access generic data (which is defined by the Society of Automotive Engineers) from the engine and transmission computers. OEM-enhanced scanners can do everything generic scanners can, plus access OEM-specific data from all of a car’s computers.

Professional repair shops have OEM-enhanced scanners that cost thousands (sometimes tens of thousands) of dollars. Meanwhile, most DIYers have inexpensive generic OBDII scanners that can only retrieve limited information from a vehicle.

Say, for example, that your car’s all-wheel drive (AWD) warning light is illuminated. With a generic OBDII scanner, you won’t be able to communicate with the AWD computer to retrieve the corresponding code(s).

Ultimately, there are many instances where you simply won’t be able to diagnose a vehicle using a generic scan tool or code reader.

Know When to Call a Professional

And that brings us to our final point: knowing when to call a professional. If you don’t want to invest tons of money in high-end scan tools and other diagnostic equipment, there might be instances where it’s best to call a professional. Modern vehicles are challenging to diagnose, and there’s no shame in calling a pro when the going gets tough.

If you’d like to move from DIY to DIFM (do it for me), consider checking out our professional installation program. All of the repair facilities within our network have undergone an extensive screening process, so you know you’re getting top-notch service—every time.