DTC will set when the following conditions are present:

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 1997 GMC Savana Special, 1997 GMC Savana Camper Special, 1997 GMC Savana, 1997 Chevrolet RV Cutaway, and 1997 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.

Engine running.
ECT is greater than 15°F (-9°C).
IAT is greater than 19°F (-7°C).
Vehicle speed is greater than one MPH.
Start-up ECT is less than 104°F (40°C).
Closed-loop timer greater than 4 minutes.
Minimum stabilized ECT is less than 68°F (20°C).