DTC Codes: Defining Diagnostic Trouble Codes

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As vehicles advance, they become more computerized and automated. Challenges that arise from this practice include increase in part prices and more complex parts overall. And, because these vehicles advance rather quickly, service shops have difficulty keeping up. Unlike the mechanics of the past, repairmen today don’t necessarily have to know the anatomy of a vehicle from top to bottom. They simply plug in your vehicle to a computer to get a diagnostics report and, in most cases, the car’s computer will highlight the issues. In fact, many vehicles today can even tell you when something’s wrong on dashboard screens. Even older vehicles have service lights to indicate vehicle issues—these are called DTC.

For today’s fleets, it’s vital to know how to read the DTC meaning. You’ll find everything you need to know about DTC below.

What Does DTC Mean?

DTC (diagnostic trouble codes), also known as OBDII codes, are your car’s system for alerting you of vehicle issues. There are typically limits for each system within your vehicle. When the vehicle detects that the issue exceeds these limits, it sends out a trouble code. Technicians use these codes to diagnose and repair vehicle issues.

Learn how to monitor fleet engine diagnostics

Trouble codes can tell you about any system issues within your vehicle, including airbags and brakes. And since all vehicles since 1996 have OBDII diagnostics, it’s unlikely you don’t have it. The challenge with this is that every model has different codes and meanings. For instance, a Ford won’t have the same codes as a Chevrolet. This makes it difficult if you’re reading the codes on your own, unless you know the codes for your specific model. In addition, the methods for repairing these issues are likely different for each make and model. Knowing the codes for your fleet vehicles is essential to proper maintenance and repair.

The Four Systems of DTC

Before DTC, diagnosing a vehicle came down to engine misfire and gross failures of parts. The advent of OBDII allowed vehicles to monitor their own systems and alert drivers as issues arise with indicator lights. Most of us recognize the most common ones: the check engine light and the oil change indicator. Today, our vehicles provide us and technicians with more information than ever before with DTC. The Society of Automotive Engineers created the original list of codes, which all vehicle manufacturers had to adopt to comply with emission regulations. European and Asian automakers adopted the same list. These codes are categorized into four main systems:

  • B-codes (body codes): Though body often refers to the outside of the vehicle, B-codes refer to features inside. More include comfort, convenience, and safety features.
  • C-codes (chassis): Functions outside of the passenger compartment including brakes, steering, and suspension.
  • U-codes (network/vehicle integration): Functions shared among the vehicle’s systems and computers.
  • P-codes (powertrain): Include functions such as the engine, transmission, and drivetrain.

Common Codes to All Manufacturers

The first thing you need to know before reading DTC is that the first letter tells you which system the code falls under. Each code has just one letter followed by four digits. As mentioned, there are common codes that each automaker follows, created to fulfill regulation requirements. Though there are thousands of additional codes unique to each model (for additional features), the generic codes remain the same. Knowing these generic codes helps you diagnose vehicle issues and repair your vehicles fast.

We’ve already covered the categories of common codes:

B: Body

C: Chassis

U: User network

P: Powertrain (i.e. engine and gearbox)

After the first letter indicating the system category, you’ll see four digits. The first digit is called a green digit and informs the technician whether or not the code is generic.

0: Generic/Global fault

1: Manufacturer/Enhanced fault

Generic codes are common and required for emission diagnosis. The enhanced or manufacturer codes are specific, meaning it’s a code relating to an additional feature specific to your vehicle.

The following three digits are purple digits, which may be hexadecimal and correspond to incremented numbers. Typically, the P family codes have sub-families defined by the first digit.

0, 1 & 2: For the air and fuel mixture

3: For ignition systems

4: For monitoring auxiliary emissions

5: For idling

6: For onboard computer and ancillary outputs

7, 8 & 9: For the transmission

There are around 11,000 definitions of these manufacturer codes—making it impossible to memorize them all. This is why you need the right equipment to read diagnostic trouble codes.

How to Read Trouble Codes

Diagnostic codes are vital to understanding when your vehicle has an issue, long before complete failure. The challenge is that, even if it tells you which system has an issue, it won’t tell you why. For example, a cylinder misfire will send a P030X code. The “X” informs you of which cylinder misfired, but that’s all the information you’ll get. So, while the system isn’t perfect, DTC gives you a huge advantage in maintenance and repair.

To read DTC, you’ll need a diagnostic connector. This scan tool will provide you with the codes in a one-line description, and may even provide the definition of the code. Basic code readers are likely to only give you the number. For the definition, you may need to keep your own database for your specific model.

Besides using a diagnostic scanner, you can also use telematics devices to monitor engine diagnostics. Telematics systems monitor your engine and systems in real-time and alerts you to issues as they arise. The right telematics system will put you ahead of the game when it comes to repairs—and hopefully keep you from any unwanted maintenance. Telematics systems can also monitor your fuel consumption, idle time, driver behavior, and much more.

Learn more about telematics and fleet tracking, at Azuga.