DTC P0126: Insufficient ECT For Stable Operation: Description
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, 2002 Chevrolet RV Cutaway, and 2002 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
While the engine is warming, the Powertrain Control Module (PCM) monitors the Engine Coolant Temperature (ECT) sensor to determine how long the engine takes to reach the coolant temperature that is required for Closed Loop operation. DTC P0126 will set if the PCM determines that the engine does not reach Closed Loop temperature in a specified amount of time. This test will not run if either the intake air or the engine coolant temperature is too low at start-up. The PCM will only run this DTC on a cold start and only once per cold start.