AutopilotDiag

OBD-II Codes

  • What does P0420 mean?
    P0420 means the engine computer detected that the catalytic converter on bank 1 is not cleaning exhaust efficiently. It's often caused by a failing converter, a bad oxygen sensor, or an exhaust leak.
  • How do I read OBD-II codes?
    Plug an OBD-II scanner into the port under the dashboard, turn the ignition on, and follow the scanner's menu to read stored codes. The scanner displays codes like P0420, which you can then look up.
  • What is the difference between P, B, C, and U codes?
    P codes are powertrain (engine, transmission), B codes are body (airbags, windows), C codes are chassis (brakes, suspension), and U codes are network (communication between modules). The letter tells you which system the fault is in.
  • Can I clear OBD-II codes myself?
    Yes, you can clear OBD-II codes with a scanner or by disconnecting the battery, but it's best to diagnose first. Clearing codes erases freeze frame data and may not fix the underlying problem.
  • What does P0300 mean?
    P0300 means your engine has random or multiple cylinder misfires. It's a generic OBD-II code that indicates misfiring is happening on more than one cylinder or in an unpredictable pattern.
  • Why does my OBD-II scanner show no codes?
    If your scanner shows no codes but the check engine light is on, it could be a communication issue, a pending code not yet stored, or a problem with the scanner itself. Some systems require specific protocols or a more advanced tool.