DTC Priority & DTC Self-Erasure
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 erased or cleared from PCM. DTCs having a high priority will overwrite the lower priority DTCs. DTC priorities and description are as listed.
- Priority "0" - 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.
After 3 good trips, PCM will turn off the MIL. Once MIL is turned off, trip counter is switched to a warm-up counter. PCM must not detect the recent malfunction during 40 warm-up cycles. A warm-up cycle is defined as the engine is started, an increase of 40°F in engine coolant temperature exists after engine is started and engine coolant temperature reaches at least 160°F (71°C).
For misfire and fuel system monitors, the component must pass the test under a Similar Conditions Window in order to record a good trip. A Similar Conditions Window is when the engine RPM is within plus or minus 375 RPM and load is within plus or minus 20 percent of when the fault occurred.
After 40 warm-up cycles with no malfunction, PCM will clear DTC from PCM. DTCs may be cleared from PCM using scan tool, but this will erase or clear OBD-II monitor data such as counter information, warm-up cycles, trips and freeze frame data.