What are DTCs or diagnostic trouble codes? What does DTC mean in a vehicle, and how does it work?

These are questions that some commercial drivers, fleet managers, and safety officers may have.

What does DTC mean?

If a vehicle has a problem, the on-board diagnostics system usually detects the issue and generates the appropriate code that you can use to identify the issue. These codes are commonly known as DTC or diagnostic trouble codes.

DTCs are how the J-1939 (in heavy-duty vehicles) and OBD-II (light-duty vehicles) indicate the on-board problems.

Each code indicates a specific fault in the vehicle. DTCs help you understand what the problem is, solve that problem quickly, and get back on the road without wasting a lot of time.

DTCs were created by the SAE (Society of Automotive Engineers), which is now known as SAE International and develops standards for automotive engineers.

Now, let’s see how a typical OBD-II code is displayed, what it means, and how to interpret it.

Format of the OBD-II DTC

A diagnostic trouble code is generally divided into four sections: one letter and four numbers. It usually has five characters.

Let’s use the following code as an example: P0430.

Here are the four sections a DTC is divided into and their detailed explanation.

1. System or category

The first letter in the code, which in this case is P, represents the system or category of the DTC. It pinpoints the related system.

The OBD-II diagnostic trouble codes are categorized into four different systems or categories:

  1. B-codes refer to the body. This category covers parts that are mainly found in the passenger compartment area and is mainly concerned with driver-related functions, such as safety and convenience.
  2. C-codes refer to the chassis category, which deals with areas outside the passenger compartment. It covers functionalities, such as brakes, suspension, steering, and mechanical systems.
  3. P-codes refer to the powertrain category. This category covers functions that include transmission, engine, and associated drivetrain accessories.
  4. U-codes refer to network and vehicle integration and cover functions managed by the on-board computer system.

As in our example (P0430), the DTC code starts with P, we know that the vehicle issue is related to the powertrain system.

2. Generic and manufacturer specific codes

The second number in the DTC represents either a generic or manufacturer specific code. Generally, you will see DTCs starting with either a 0 or 1.

DTCs that start with 0 as the first digit after the letter that represents the system refer to generic codes. In other words, 0 refers to generic faults. It represents a generic code that is followed by all OBD-II vehicles.

On the other hand, codes starting with 1 are manufacturer specific codes. These codes are unique to the specific model of the vehicle.

In our example of P0430, the first number is 0, which means it is a generic code.

3. Subsystems

The third character (number) in the diagnostic trouble code indicates the subsystem in which the fault is.

The powertrain category (P) has eight subsystems:

  • 0 – Fuel and air metering and auxiliary emission controls
  • 1 – Fuel and air metering
  • 2 – Fuel and air metering – injector circuit
  • 3 – Ignition systems
  • 4 – Auxiliary emission controls
  • 5 – Vehicle speed control and engine idling
  • 6 – Computer and auxiliary outputs
  • 7 – Transmission

Sometimes, you may also see a letter (A, B, or C) instead of a number in the DTC. In that case, these three letters refer to the hybrid propulsion systems.

In our example, the third character (P0430) represents an issue with auxiliary emission controls.

4. Fault code description

The last two numbers (sometimes, three) in the DTC refer to the actual fault description. It can be any number between 0 to 99.

In our example (P0430), it is 30, which indicates that the catalyst system efficiency is below the threshold. There could be multiple reasons for that, e.g., a faulty catalytic converter, engine mechanical damage, exhaust leak, or a leaking fuel injector.

You can check the complete list of OBD-II fault code descriptions here.

Here is a graphical representation of diagnostic trouble codes are interpreted.

How Motive helps with fault code detection and vehicle maintenance

DTCs or diagnostic trouble codes can help pinpoint the exact issue in a vehicle. Vehicle downtime is a problem that companies may struggle with. Downtime hampers their customer service, productivity, and profitability.

If you have the Motive vehicle fleet management solution installed, these DTC codes can be redirected to safety and dispatchers. These managers can then take immediate action to keep disruptions to a minimum.

The Motive Vehicle Gateway automatically monitors fault codes and can send instant, real-time alerts to the Motive Dashboard and fleet managers with actionable descriptions if an issue occurs.

Recurring issues are also highlighted, so you can identify important issues faster.

Drivers can also report a defect while creating vehicle inspection reports with the Motive App, which also sends an alert in the Motive Dashboard.

Furthermore, you can also view the fault code detail reports for any vehicle or group for a specific time period to anticipate when maintenance will be required. These reports can also be exported and downloaded in your preferred format (CSV or PDF).

Timely identification of DTCs may increase efficiency and save money

By timely identifying vehicle-related issues with the Motive fleet management solution, you may avoid costly repairs, minimize vehicle downtime, provide better service to your customers, and increase profitability.

As more data is gathered, you can also look into historical reports, identify recurring issues, and stay on top of your vehicle health for smooth operations across the entire fleet.

Learn more about DTC codes in our guide.