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OBD2 codes

Look up an OBD2 trouble code.

Have a code from a scanner or a repair estimate? Find its meaning and what to check next in 65 free public guides.

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How to read an OBD2 code with MECH AI — watch on its own page

What is an OBD2 code?

An OBD2 code — also called a DTC (Diagnostic Trouble Code) — is a five-character code your car’s computer stores when it detects a fault. The first letter is the system (P = powertrain, B = body, C = chassis, U = network) and the digits identify the specific problem. For example, P0420 means the catalytic converter is below its efficiency threshold. A code tells you where to look — confirming the actual cause still takes diagnosis.

All 65 OBD2 code guides

Each guide explains the code and suggests checks. Pick your vehicle where coverage is available.

OBD2 code FAQ

What is an OBD2 code?
An OBD2 code (also called a DTC, or Diagnostic Trouble Code) is a five-character code your car's computer stores when it detects a fault — for example, P0420 means the catalytic converter is below its efficiency threshold. The letter shows the system (P = powertrain, B = body, C = chassis, U = network) and the digits narrow down the specific fault. A code tells you where to look; confirming the actual cause still takes diagnosis.
How do I read an OBD2 code?
Plug an OBD2 scanner into the port under the dashboard (usually below the steering column), turn the key to "on," and read the stored code. The MECH AI iOS and Android app can do this directly — pair a Bluetooth LE (BLE) or WiFi ELM327 adapter and it reads stored, pending, and permanent codes free, with plain-English descriptions (read-only). Already have a code? Enter it above or find it in the list to open its public guide if available.
Is it safe to drive with a check engine light on?
A code alone cannot tell you whether your vehicle is safe to drive. Follow the warning instructions in your owner’s manual and get a qualified assessment if you are unsure. The public guides explain what a code means; they cannot inspect your vehicle.
Does clearing a code fix the problem?
No. Clearing a code only turns the light off — if the underlying fault is still present, the code returns once the car re-runs the relevant monitor. Diagnose and repair the root cause first; clear the code afterward to confirm the fix held.

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