Car Fault Codes
Instant Lookup
Enter an OBD-II code to get fault description, possible causes, and repair solutions.
Covering all P / B / C / U standard diagnostic trouble codes.
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OBD-II codes start with a letter indicating the affected system category
Most Searched Fault Codes
The diagnostic trouble codes most frequently looked up by drivers and technicians
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Some manufacturers have brand-specific fault code definitions for more precise diagnostics
What Are OBD-II Fault Codes?
OBD-II (On-Board Diagnostics II) is the second generation of the standardized on-board diagnostic system, mandated in the United States since 1996 and now adopted globally by the automotive industry. When a vehicle's computer detects a malfunction, it stores a standardized Diagnostic Trouble Code (DTC) that technicians can read through the OBD diagnostic port to pinpoint the problem.
Code Structure
A standard OBD-II code consists of 5 characters: the 1st character is a letter (P/B/C/U) indicating the system category; the 2nd digit indicates whether the code is SAE-standard (0) or manufacturer-specific (1); the 3rd digit identifies the specific subsystem; the 4th and 5th digits identify the specific fault number.
Prefix Meanings
- P (Powertrain) — Powertrain faults including engine and transmission. This is the most common code type.
- B (Body) — Body system faults including airbags, HVAC, power windows, and other body electronics.
- C (Chassis) — Chassis system faults including ABS, brake systems, suspension, and steering.
- U (Network) — Communication network faults including CAN bus and inter-module communication issues.
What to Do When the Check Engine Light Comes On
When the Malfunction Indicator Lamp (MIL) illuminates, don't panic. If the light is steady and the vehicle drives normally, you can continue driving but should get it checked soon. If the light is flashing, it indicates a severe misfire that could damage the catalytic converter — pull over and shut off the engine as soon as safely possible. Use an OBD-II scanner to read the specific code, then look it up on this site to understand the possible causes and solutions before deciding whether to DIY or visit a repair shop.