Diagnostic Trouble Codes (DTCs)

The Diagnostic Trouble Codes (DTCs) set in order to indicate that the IPC has detected a malfunction in a particular circuit or other system. The IPC's program follows routines for internal checks, but only under prescribed conditions (Test Conditions). When these conditions exist, the IPC evaluates certain circuits or systems for a malfunction (Failure Conditions). When the failure conditions are true, a DTC is set as a current DTC. Some DTCs command that the IPC illuminate the Service Engine Soon indicator.

The IPC's EEPROM does not store the DTCs. Therefore, the DTCs do not remain after a battery disconnect.

Current DTCs
When the IPC determines that the test conditions and failure conditions for a particular DTC are true, the IPC sets that DTC as current. All of the DTCs remain current at least until the next time the IPC finds the test conditions are true and the failure conditions are false. A few DTCs remain current until the next ignition cycle or until the failure conditions are false several times.

History DTCs
After a DTC has been set, the IPC continues to monitor for the test and failure conditions. For most DTCs, if the test conditions are true and the failure conditions are false, the DTC becomes a history DTC. Some of the DTCs require the test conditions to be true and failure conditions to be false several times. Some of the DTCs require an ignition cycle in order to change from current to history. If no current DTCs are present for a period of 50 ignition cycles, all of the history DTCs clear.