Vehicle manufacturers employ DTC’s to identify any problems and issues with the model. What does “DTC” mean? The letters spell out as Diagnostic Trouble Codes. Others refer to DTC’s as “fault codes.” A DTC is five characters long. There are thousands of codes out there, but you’ll get the hang of them after understanding the meaning of each character.

DTC’s fall into two categories: regular diagnostic trouble codes (DTCs) and permanent diagnostic trouble codes (PD DTC codes). While you can reset and clear your vehicle’s battery for regular DTCs, PD DTCs can only be cleared when you fix the problem it indicates.

DTC’s: Letter by Letter

How do you read a DTC code? To find out the DTC codes meaning, you need to know what each letter stands for and the DTC number definitions.

The first character of the DTC indicates which part of the vehicle has a problem. It also shows the category of the DTC. The first letter used stands for the part that needs fixing.

  1. P for powertrain, which covers the transmission, engine, and associated accessories.
  2. What are B codes? B for the body or all parts in the passenger compartment.
  3. U indicates the vehicle integration and network, or what the onboard computer system manages in terms of functions.
  4. C stands for the chassis or the mechanical systems and functions

The second character is a number—either 0 or 1. Zero (0) is the standardized, generic, or global code and can follow SAE definitions. One (1) indicated a manufacturer-specific code.

The following or third character is also a number and ranges from one to 8. This number indicates the vehicle subsystem at fault:

0 refers to the fuel and air metering plus the auxiliary emission controls.

1 refers to the fuel and air metering.

2 also refers to the fuel and air metering but the injector circuit in particular.

3 indicates the ignition system or misfires.

4 or DTC 4 is for the auxiliary emission controls.

5 is the vehicle speed control, auxiliary input, and idle control systems.

6 stands for the output circuit and computer.

7 indicates the transmission.

The fourth and fifth characters define what problem the vehicle is experiencing. The numbers can range from 0 to 99. To know the meaning of the last two characters or numbers, you will have to download the DTC codes list PDF specific to your vehicle. Make sure that all your fleet drivers also have a copy of this on their device so they can easily access it without using data or internet.

How to interpret DTC Fault Codes

Now that you know what each character or number stands for, what do these diagnostic codes mean? The combination of characters will refer to a vehicle malfunction that needs fixing. Using the common DTC P0101, you’ll have to follow these steps to correctly interpret them:

  1. Refer to the list above to know what each character stands for.
  2. First letter is P, so this indicates the powertrain is the problem.
  3. Since the second character is 0, this shows that the code is not specific to a manufacturer. You can use SAE definitions to interpret this.
  4. The third character, 1, specifies the issue is found in the fuel and air metering.
  5. The last two digits indicate the problem most specifically. You will need the list included with your vehicle. For this example, the P0101 refers to a common problem of the mass air flow (MAF) circuit or sensor fault.

The DTC information identifies what is wrong with the vehicle. Having a quick reference and being able to interpret the DTC codes meaning leads mechanics to what needs to be done. From there, they can make a thorough assessment and find the reason behind the malfunction.

Having an electronic diagnostic system speeds up the process of relaying the code to fleet managers and maintenance staff. You may want to invest in a fleet safety system like Netradyne’s to streamline communication between fleet drivers and managers. Having a fast and efficient electronic system in place ensures that the problem is resolved immediately, while helping you manage the replacement truck to continue the job.

You can also employ the camera installed in the truck to witness the issue and diagnose the problem in real time, even from a distance. You are able to react immediately and ensure the safety of all without the physical presence.

Final Thoughts

DTCs enable faster communication and efficient management of common vehicle problems. Once you have the DTC code information, you’ll be able to find the root cause and take the steps to fix it.

Be sure to have a reliable system that lets them communicate these codes. Visit Netradyne to know more about such fleet safety systems.

Read Everything You Need to Know About DTC Codes on our latest blog.


  1. What does a 0 DTC code mean?

    A DTC code with a zero as the second digit indicates that the code is universally applicable and can be found across different vehicle makes and models. In other words, it is not limited to a specific manufacturer.

  2. What does a DTC mean if the second digit is a 1?
  3. When the second digit of a DTC code is 1, it signifies that the code is manufacturer-specific. This means that the problem indicated by the code is not a common issue across all vehicles, but rather unique to a particular manufacturer or specific models.

  4. What is DTC memory?
    DTC memory refers to a storage system within the On-Board Diagnostics (OBD) system. Each identified DTC is stored in this memory, allowing diagnostic tools to easily access and retrieve the codes. It plays a crucial role in cataloging DTCs and helps in planning future preventative maintenance for the vehicle.

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