Conditions For Clearing MIL/DTC

WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. 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 test runs and passes.
The ECM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the ECM.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are present by this diagnostic or any other emission-related diagnostic.
A scan tool can clear the MIL/DTC.