OBD2 Codes List — Complete Diagnostic Guide

OBD2 (On-Board Diagnostics II) codes are standardized diagnostic trouble codes (DTCs) that your car's computer stores when it detects a problem. They're read with an OBD2 scanner plugged into the 16-pin port under your dashboard. Every car sold in the US after 1996 is required to support OBD2. The codes follow a pattern: P (Powertrain), B (Body), C (Chassis), or U (Network), followed by 4 digits that identify the specific fault.

You need an OBD2 scanner — a handheld device or Bluetooth adapter that plugs into your car's OBD2 port (usually under the dashboard on the driver's side). Plug in the scanner, turn the ignition to "on" (don't start the engine), and it will read any stored trouble codes. You can also use WrenchAI's free AI diagnosis tool: enter your code and get an instant breakdown of causes, fixes, and repair costs.

The second digit in an OBD2 code tells you who defined it: P0 codes are generic/global codes defined by SAE and used by all manufacturers — they're the most common and well-documented. P1 codes are manufacturer-specific (each automaker defines their own P1xxx codes for proprietary systems). P2 codes are generic codes that were added in later OBD2 expansions. P3 codes are also manufacturer-specific. When in doubt, start with P0 codes — they're standardized and apply across all makes and models.

It depends on whether the light is steady or flashing. A steady check engine light means a fault was detected — the car is drivable for short distances but you should diagnose it soon. A flashing check engine light is an emergency: it means your engine is misfiring severely enough to damage your catalytic converter within minutes. Pull over safely and don't drive further until the fault is fixed. Ignoring a flashing CEL can turn a $60 spark plug replacement into a $1,500 catalytic converter job.