DTC P0128: ECT Less Than Thermostat Regulating Temperature: Description

WARNING: This page is about a different car, the 2001 GMC Savana, 2001 Chevrolet RV Cutaway, 2001 Chevrolet Cutaway, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

Engine Coolant Temperature (ECT) sensor monitors temperature of coolant. This input is used by Powertrain Control Module (PCM) for engine control and as an enabling criteria for some diagnostics. Airflow coming into engine is accumulated and used to determine if engine has been driven within normal conditions. That is, conditions that would allow engine coolant to heat up normally to thermostat regulating temperature. If coolant temperature does not increase normally or does not reach regulating temperature of thermostat, problems with diagnostics may occur. Diagnostics that use ECT as an enabling criteria, may not run when expected. DTC will only run once per ignition cycle within code enable criteria. DTC P0128 will set if engine coolant fails to reach a preset target temperature before a calculated airflow is accumulated.