DTC will set when the following conditions are present:

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 1997 GMC Yukon, 1997 GMC Suburban, 1997 GMC Pickup, 1997 GMC Cab & Chassis, and 1997 Chevrolet Tahoe. 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).