Diagnostic Trouble Codes (DTCS)

With OBD II, different DTC faults have different priorities according to regulations. As a result, the priorities determine MIL illumination and DTC erasure. DTCs are entered according to individual priority. DTCs with a higher priority overwrite lower priority DTCs.

Priorities

1. Priority 1 One-Trip Failure of Non-Fuel or Non-Misfire Fault (e.g, Cat Mon Failure)
2. Priority 3 Matured Fault (either One-Trip or Two-Trip) Non-Fuel & Non-Misfire
3. Priority 4 One-Trip Failure of Fuel System or Misfire Fault
4. Priority 6 Matured Fault for Fuel System or Misfire (either One-Trip or Two-Trip)

Non-emissions related failures have no priority. One trip failures of two trip faults have low priority. Two trip failures or matured faults have higher priority. One and two trip failures of fuel system and misfire monitor take precedence over non-fuel system and non-misfire failures.