What Is DTC (Diagnostic Trouble Code)?

A standardized alphanumeric code stored by the OBD-II system when a vehicle malfunction is detected.

DTCs follow a standard format: one letter (P, B, C, or U) followed by four digits. They are classified as generic (SAE standard, second digit 0) or manufacturer-specific (second digit 1). DTCs can be stored, pending, or permanent. Stored codes set the Check Engine Light, pending codes are detected but not yet confirmed, and permanent codes cannot be cleared until the underlying issue is fixed.