OBD2 Trouble Codes (DTC) Library
Diagnostic Trouble Codes, or DTCs, are codes stored by vehicle control modules when a fault is detected. Browse our reviewed OBD2 trouble code guides, organized into the four main diagnostic families: Powertrain, Chassis, Body and Network Communication.
Browse OBD2 Codes by System
Engine, fuel and air metering, ignition, emissions, turbocharging and transmission diagnostic trouble codes.
Browse Powertrain Codes →ABS, braking, wheel-speed, stability-control, steering, suspension and other chassis-system trouble codes.
Browse Chassis Codes →Airbag, climate control, lighting, security, seats, doors and other electronic body-system trouble codes.
Browse Body Codes →CAN bus, module communication and other electronic vehicle-network diagnostic trouble codes.
Browse Network Codes →What Is an OBD2 Diagnostic Trouble Code?
A Diagnostic Trouble Code is stored when a vehicle control module detects a condition outside its expected operating range. The code helps identify the system in which the fault was detected, but it does not always identify the component that must be replaced.
A complete diagnosis can involve checking other stored codes, live sensor data, wiring, connectors, power supplies and vehicle-specific service information.
What Do P, C, B and U Codes Mean?
| Prefix | System | Typical areas |
|---|---|---|
| P | Powertrain | Engine, fuel, ignition, emissions and transmission |
| C | Chassis | ABS, brakes, steering, stability and suspension |
| B | Body | Airbags, climate control, lighting and body electronics |
| U | Network | CAN bus and communication between electronic modules |
How to Read an OBD2 Code
A diagnostic trouble code normally contains one letter followed by four characters. The first letter identifies the main vehicle system. For example, P0300 is a Powertrain code because it begins with the letter P.
The following characters identify the diagnostic range and individual fault. Some DTC definitions are standardized while others are defined by the vehicle manufacturer, so the exact vehicle make, model and year can be important when interpreting a code.
Search for a Trouble Code
Enter a code such as P0420, P0300 or U0415 to search the OBD2.com diagnostic library.
How to Diagnose an OBD2 Trouble Code
Start by recording all stored, pending and permanent codes before clearing anything. Multiple codes can point to a shared electrical, mechanical or communication problem.
Use the code definition as the starting point of the diagnosis rather than replacing the component named in the description immediately. Check relevant wiring, connectors, sensor readings and system operation before replacing parts.
OBD2 Trouble Codes FAQ
What does DTC mean?
DTC stands for Diagnostic Trouble Code. It is an alphanumeric code stored by a vehicle control module when a monitored fault is detected.
Can a basic OBD2 scanner read every DTC?
No. Basic OBD2 readers generally focus on engine and emissions-related Powertrain codes. Reading ABS, airbag, body, steering and other control modules requires a diagnostic tool that supports those vehicle systems.
Should I replace the part named in the code?
Not automatically. A trouble code identifies the system and fault detected by the vehicle. Wiring faults, connectors, voltage problems, sensors or another component can produce the same code.
Can I clear an OBD2 code?
A diagnostic scanner can clear many stored codes, but the code may return if the underlying fault has not been corrected.
