DTC Priority

With OBD-II, different OBD-II related DTCs have different priorities according to regulations. The DTC priority determines when MIL will be turned on and DTC is cleared/erased from PCM. DTCs having a high priority will overwrite the lower priority DTCs. DTC priorities and description are as listed.

• Priority "O"
  
  This is a non-emissions related DTC.
• Priority "1"
  
  One trip failure of a 2-trip DTC for non-fuel system and non-misfire conditions.
• Priority "2"
  
  One trip failure of a 2-trip DTC for fuel system rich or fuel system lean condition, or misfire condition.
• Priority "3"
  
  Second trip failure for non-fuel system or non-misfire condition, or a one-trip failure.
• Priority "4"
  
  Second trip failure for fuel system rich or fuel system lean and misfire condition, or a one-trip catalyst damaging misfire.

One trip failures on a 2-trip DTC have low priority and 2-trip failures have higher priority. One-trip and 2-trip failures for fuel system monitor and misfire monitor take precedence over non-fuel system and non-misfire failures. Non-emission related DTCs have no priority in which they are entered in the PCM.