DTC P0128: ECT Less Than Thermostat Regulating Temperature: Description

WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

An Engine Coolant Temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the Powertrain Control Module (PCM) for engine control, and as an enabling criteria for some diagnostics.

The airflow that is coming into the engine is accumulated. The accumulated airflow determines if the vehicle has been driven within conditions allowing the engine coolant to heat up to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach regulating temperature of the thermostat, diagnostics that use ECT as enabling criteria, may not run when expected.

This DTC will only run once per ignition cycle within the enabling condition. If engine coolant fails to reach a present target temperature before a calculated airflow is accumulated, DTC P0128 sets.