Conditions For Clearing MIL/DTC

WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
The history DTC will clear after the PCM runs and passes 40 consecutive warm up cycles with no failure.
The DTC can be cleared by using a scan tool.