Conditions for Clearing the MIL/DTC

WARNING: This page is about a different car, the 2007 Pontiac G5 Pursuit, 2007 Pontiac G5, and 2007 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.

The ECM turns OFF the MIL during the third consecutive trip in which the diagnostic runs and passes.
A scan tool can clear the MIL/DTC.
The ECM clears the DTC from ECM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
The ECM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the ECM.