Conditions For Clearing MIL/DTC

The PCM turns off the MIL lamp after 3 consecutive ignition cycles that the diagnostic runs and passes.
A current, DTC last test fails, clears when the diagnostic runs and passes.
A DTC stored in history clears after 40 warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
A scan tool can be used to clear the DTC.