Diagnostic Trouble Codes(DTC) and everything you need to know
What is DTC
DTC faults or Diagnostic Trouble Codes are the codes generated and stored by a vehicle’s Onboard Diagnostic system indicating that a part or section of the vehicle is malfunctioning.
DTC Codes identify a specific problem area. Technicians can use the codes to diagnose the problem is causing the OBD to report the fault.
On-board diagnostic systems (OBD) have undergone a considerable evolution from 1996 when they were first introduced in the US, and so have the protocols that the computer uses to respond to the DTC faults.
Every vehicle with an OBD also comes with a manual for fault codes. The manual is what a professional or any knowledgeable driver can use to determine the systems, components, and circuits that he or she should test to diagnose the vehicle’s fault.
Interpreting DTC codes
A DTC code is five characters long. You’ll get more familiar with these over time, but there are thousands of different codes so as a driver or fleet owner, you want to know how to find the definition for any code you see in your vehicle. If you have a good comprehensive fleet management solution, the meaning of each code will be provided to you each time you are alerted with a code.
Codes are standard, and you’ll know what area of your vehicle the code refers to if you understand the structure of the code and the standard abbreviations.
The first character (letter)
OBD-II codes start with a letter that denotes the part of the vehicle that has a fault.
P – Powertrain. Includes engine, transmission and associated accessories.
C – Chassis. Covers mechanical systems and functions: steering, suspension, and braking.
B – Body. Parts mainly found in the passenger compartment area.
U – Network & vehicle integration. Functions managed by the onboard computer system.
The second character (number)
The first letter is followed by a number, usually 0 or 1.
0 – Standardized (SAE) code, also known as generic code (sometimes called global)
1 – Manufacturer-specific code (sometimes called enhanced)
The third character (number)
For powertrain codes, this number tells you which vehicle subsystem has a fault. There are eight:
0 – Fuel and air metering and auxiliary emission controls
1 – Fuel and air metering
2 – Fuel and air metering – injector circuit
3 – Ignition systems or misfires
4 – Auxiliary emission controls
5 – Vehicle speed control, idle control systems and auxiliary inputs
6 – Computer and output circuit
7 – Transmission
You may also see an A, B or C, which can refer to hybrid propulsion systems.
For other families of codes, refer to the definitions provided by your manufacturer.
The fourth and fifth characters (number)
The final piece of a DTC is a number that defines the exact problem that you’re experiencing. It can be a number between zero and 99.
Here’s an example of a complete code:
P0782 means powertrain, generic, transmission, 2-3 shift malfunction.
The best source for DTC meanings is the dealer that sold or leased the truck to you or the manufacturer who made it. Some DTCs are specific to the vehicle. Download the complete list to your device so that you can access it any time, including in areas where cellular service may be spotty. Or consider implementing a vehicle diagnostics software solution that provides definitions for you.