Conditions For Clearing MIL/DTC

WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

PCM turns OFF MIL after 3 consecutive ignition cycles that the diagnostic runs and passes.
A current, DTC last test fails, clears when 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.