DTC P0128-00: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature): General Description

An Engine Coolant Temperature Sensor (ECTS) monitors the temperature of the coolant. This input is used by the ECM for engine control and as an enabling criteria for same diagnostics. The air flow coming into the engine is accumulated and used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature.