OBD2 Error Code Lookup
Search any check engine code to see the cause, typical repair cost, and severity. Type a code like P0300 or P0420.
| Code | Description & Causes | Typical Cost | Severity |
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What Is OBD2?
OBD2 (On-Board Diagnostics, 2nd generation) is a standardized vehicle self-diagnostic system required on all US cars and light trucks sold after 1996. It monitors hundreds of sensors and systems and stores fault codes when it detects something outside normal parameters. The standardized 16-pin DLC (Data Link Connector) port is typically located under the dash on the driver's side.
How to Read Codes
You need an OBD2 scanner to read stored codes. Basic scanners cost $20–50 at auto parts stores and are a one-time investment. Many auto parts retailers (AutoZone, O'Reilly, Advance Auto Parts) will read codes for free. Smartphone-based Bluetooth OBD2 adapters (ELM327) paired with apps like Torque Pro or OBD Fusion can display live sensor data beyond just codes. More advanced bidirectional scanners ($150–500) can clear codes and perform actuator tests.
Pending vs. Confirmed Codes
A pending (or "maturing") code means the ECU has detected an issue once but not enough times to illuminate the check engine light. A confirmed (or "current") code has been detected on multiple drive cycles and triggers the MIL (Malfunction Indicator Lamp). Permanent codes cannot be cleared by simply disconnecting the battery — they require the underlying issue to be fixed and the system to run a successful self-test.
Why Clearing Codes Without Fixing the Problem Makes It Worse
Clearing a code without repair resets all readiness monitors — the completed self-tests the ECU runs. Most states require multiple monitors to be "ready" to pass an emissions inspection. If you clear codes right before an inspection, you'll likely fail for "not ready" status even without an active code. The code will also return once the conditions that triggered it occur again, often within one or two drive cycles.
Buying a Basic OBD2 Scanner
A $20–50 scanner from Amazon, Harbor Freight, or AutoZone can read and clear standard OBD2 codes on any 1996+ vehicle. Look for one that shows freeze frame data (the sensor readings at the moment the code set) — this is invaluable for diagnosis. The Autel AL319, BAFX Bluetooth adapter, and Innova 3100 are reliable budget options. Avoid the cheapest no-name adapters for Bluetooth models, as some have firmware issues.