Conditions For Clearing MIL/DTC

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.

The PCM turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
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 MIL and DTC.