OBD-II Code Lookup
Decode Your Check Engine Light.
Enter any OBD-II code (like P0300, P0420, P0171) for plain-English explanations, symptoms, causes, and repair cost estimates. No ads, no signup, no fluff.
Type a code or keyword. Press Enter to open, or click a result.
Most Common Codes
Start with these — they cover 80% of check engine lights.
What is an OBD-II code?
OBD-II (On-Board Diagnostics, version 2) is a standardized system every car sold in the US since 1996 must have. When your check engine light comes on, the car has stored a code telling you exactly what it detected. These codes are public-standard — any OBD reader can pull them, from $20 consumer tools to professional diagnostic systems.
Every OBD-II code is a five-character string: one letter and four digits. The letter identifies the system (P for powertrain, B for body, C for chassis, U for network). The first digit tells you whether the code is generic or manufacturer-specific. The next three digits pinpoint the subsystem and specific fault.
A code like P0420 means “Catalyst System Efficiency Below Threshold, Bank 1” — every make and model uses that same five characters for the same fault, which is why a universal scanner works across every vehicle regardless of brand.
How do I read the code on my car?
You need an OBD-II scanner. Consumer tools start around $20 (corded) or $30-50 (Bluetooth dongles that pair with phone apps). Plug into the OBD port — usually under the dashboard near the steering column — turn the key to accessory (don't start), and the scanner reads the code.
Auto parts stores (AutoZone, O'Reilly, Advance) will often read your code for free. They will try to sell you parts they think might fix it — be cautious, some of those guesses are wrong.
What does each letter mean?
- P — Powertrain (engine and transmission). Most codes fall here.
- B — Body (airbags, lighting, HVAC)
- C — Chassis (brakes, ABS, suspension)
- U — Network/communication between modules
The second digit tells you if the code is generic (0 or 2) or manufacturer-specific (1 or 3). Generic codes have the same meaning on any car; manufacturer codes vary by brand.
Can I drive with a check engine light on?
It depends on the code. A solid check engine light usually means you can drive home but should get it checked soon. A flashingcheck engine light means there's active damage happening (usually a severe misfire damaging the catalytic converter) — pull over safely and get it towed.
When you look up a code on this page, we tell you specifically whether it's safe to keep driving.
Is this OBD lookup free?
Yes, always. We don't charge, don't ask you to sign up, don't serve ads, and don't sell your data. The OBD-II code definitions are public-domain SAE standards — they belong to everyone.
What can't an OBD-II code tell you?
- Exactly which part is bad. P0300 tells you there's a misfire, not whether it's spark plugs, coils, or compression.
- If the code is the real problem. Sometimes the stored code is a symptom of a bigger issue.
- Pending codes. Some intermittent issues set “pending” codes that only a higher-end scanner can read.
- Live data. Real diagnostics often require watching sensor data in real time — this is where shop-grade scanners shine.
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Build My Shop Site →Frequently asked questions
What does a P code mean?
P stands for Powertrain — the engine, transmission, and emissions systems. The first digit after the letter is 0 or 2 for generic codes (identical meaning across all brands) and 1 or 3 for manufacturer-specific codes. P0xxx codes are the most common and the definitions you find online are reliable.
Can I clear my own OBD-II codes?
Yes, with any OBD-II scanner. A $25 Bluetooth dongle paired with a phone app can read and clear codes. Clearing without fixing the underlying issue means the light returns — sometimes within miles, sometimes after a few drive cycles once the condition reoccurs.
Will clearing a code pass an emissions inspection?
Usually no. After codes are cleared, the car's onboard monitors reset to "not ready." Most state inspection programs fail a vehicle with more than one or two monitors in the not-ready state. Drive at least 100 miles of mixed city and highway before re-testing so the monitors can re-run.
What is the difference between pending and stored codes?
A pending code means a fault was detected once and is being monitored. A stored (confirmed) code means the fault has occurred on consecutive drive cycles and the check engine light is on. Pending codes often clear themselves if the condition does not repeat — stored codes require intervention.
What does a manufacturer-specific code mean?
Codes starting with P1 or P3 (also B1/B3, C1/C3, U1/U3) are manufacturer-specific. Meaning varies by brand, year, and sometimes engine. Our database covers the most common generic codes; for a P1xxx code on a specific vehicle, consult a brand-specific service manual or forum.
When should I stop looking up codes and go to a shop?
Take it to a shop when: the check engine light flashes (active damage), the code relates to a safety system like ABS or airbags, you see a transmission or critical sensor code, you cannot identify the failing part after testing, or the same code returns repeatedly after clearing. Diagnostic time is cheaper than guessed repairs.
Why did my check engine light turn off by itself?
Some faults are intermittent — a loose gas cap, a single misfire, a transient sensor glitch. If the ECU doesn't see the same fault across three consecutive drive cycles, the light turns off automatically and the code moves from "stored" to "history." The underlying root cause may still be there; keep an eye on it.
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