Enter a diagnostic trouble code or search by symptom to get plain-English explanations, severity levels, and estimated repair costs.
Enter a diagnostic code or search by symptom to get started.
For informational purposes only. Diagnostic trouble codes are starting points for diagnosis, not definitive answers. Always consult a certified mechanic for proper diagnosis and repair. Estimated costs vary by vehicle, location, and shop rates.
Everything you need to know about on-board diagnostics and how your car communicates problems.
OBD-II (On-Board Diagnostics, second generation) is a standardized computer system built into every modern vehicle. It continuously monitors your engine, transmission, emissions equipment, and other critical systems. When something goes wrong, the OBD-II system detects the issue, turns on your check engine light, and stores a specific diagnostic trouble code (DTC) that identifies the problem.
OBD-II gives you the power to understand what’s happening inside your car before a small issue becomes an expensive repair. It’s the same system mechanics use to diagnose problems — and with an affordable scanner, you can read the codes yourself. It also plays a key role in emissions testing, helping keep vehicles running cleaner.
The original OBD-I systems appeared in the early 1980s, but they varied wildly between manufacturers — each brand had its own codes, connectors, and protocols. In 1996, the U.S. government mandated OBD-II for all cars and light trucks sold in America. OBD-II standardized everything: a universal 16-pin connector, a shared set of diagnostic codes, and consistent communication protocols. This means any OBD-II scanner works with any 1996-or-newer vehicle, regardless of make.
Every DTC follows a standard five-character format. The first letter tells you which vehicle system is affected:
The remaining characters narrow down the exact fault. For example, P0300 means a random/multiple cylinder misfire in the powertrain system. Use the search tool above to look up any code and get a plain-English explanation.
On most vehicles, the OBD-II port is located under the dashboard on the driver’s side, usually near the steering column. It’s a 16-pin trapezoidal connector that faces downward.
Sit in the driver's seat and look under the dashboard, to the left of the steering wheel.
Check near the fuse panel area or just above the pedals. Some vehicles have a small cover over the port.
Plug in your OBD-II scanner — it should fit snugly into the 16-pin connector. Turn the ignition to "On" (engine off) to start reading codes.
Common questions about OBD-II diagnostics and trouble codes.
OBD stands for On-Board Diagnostics. It refers to a vehicle's built-in computer system that monitors engine performance, emissions, and other critical systems. OBD-II is the second generation of this technology, standardized across all vehicles sold in the U.S. since 1996.
All gasoline cars and light trucks sold in the United States since 1996 are required to have OBD-II systems. Diesel vehicles followed in 1997. If your car was manufactured before 1996, it may have the older OBD-I system or no standardized diagnostic port at all.
OBD-I (pre-1996) varied by manufacturer — each brand had different connectors, codes, and protocols. OBD-II standardized everything: a universal 16-pin port, shared diagnostic codes, and consistent communication protocols. This means one scanner can read codes from any OBD-II vehicle, regardless of make or model.
Yes, most electric vehicles have an OBD-II port because it's legally required. However, EVs often use the port primarily for emissions compliance reporting and may not expose as much diagnostic data through standard OBD-II protocols. Many EV manufacturers use proprietary systems for deeper diagnostics, accessible through brand-specific apps or dealer tools.
You need an OBD-II scanner (also called a code reader). Basic scanners that read and clear codes start around $20–$30. More advanced scanners offer live data, freeze frame data, and manufacturer-specific codes. You can also use a Bluetooth OBD-II adapter paired with a smartphone app — popular options include BlueDriver, FIXD, and the ELM327 adapter with the Torque app.
Generic (SAE standard) codes starting with P0, P2, P3, B0, C0, and U0 are the same across all manufacturers. However, manufacturer-specific codes (starting with P1, B1, C1, U1, etc.) are unique to each brand. These proprietary codes cover systems and features specific to that manufacturer.
It depends on the severity. A steady check engine light usually indicates a non-emergency issue — the car is safe to drive short distances, but you should get it diagnosed soon. A flashing check engine light means a severe problem (often a misfire that can damage the catalytic converter) and you should pull over safely and avoid driving until it's repaired.