AutoDiag: Master OBD-II Code Database

OBD-II Master Lookup

B, C, U, & P Codes Diagnostic Database

What is a DTC?

A Diagnostic Trouble Code (DTC) is a series of alphanumeric codes used by a vehicle's onboard computer (OBD-II) to identify specific problems. When the vehicle’s sensors detect that a component is operating outside its normal range, the Engine Control Unit (ECU) triggers a DTC and usually illuminates the "Check Engine" light.

These codes are part of a universal system designed to help mechanics and vehicle owners quickly narrow down the root cause of a malfunction. Instead of guessing, a technician can read the code to determine if the issue is related to the fuel system, ignition, emissions, or electronic sensors. Understanding these codes is the first step in maintaining vehicle health and ensuring optimal fuel efficiency and safety.

Understanding Code Types

OBD-II codes are broken down into four main categories, identified by the first letter of the code:

  • P (Powertrain): Covers the engine, transmission, and fuel system. These are the most common codes.
  • B (Body): Relates to components inside the passenger compartment, such as airbags, climate control, and power seats.
  • C (Chassis): Associated with mechanical systems outside the cabin, like ABS brakes, steering, and suspension.
  • U (Network): Refers to communication issues between the different computer modules within the vehicle.

How to Use an OBD-II Scanner

  1. Locate the Port: Find the 16-pin OBD-II Data Link Connector (DLC), usually located under the dashboard on the driver's side.
  2. Plug in the Device: Insert your OBD-II scanner or Bluetooth adapter while the ignition is OFF.
  3. Turn Ignition ON: Turn the key to the 'ON' position (or start the engine if required by the device).
  4. Read the Code: Use the scanner to "Read Codes." You will receive a code like P0101.
  5. Lookup: Enter that code into our search tool above to get the professional description and system category.

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