Circuit Description

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

This diagnostic monitors the relationship between engine coolant temperature and the engine running time. The engine coolant temperature (ECT) sensor signal is used to monitor the performance of the engine cooling system thermostat. A DTC P0128 may set if the ECT sensor voltage does not indicate that the engine coolant temperature has increased sufficiently during running of the diagnostic. When the ambient air temperature and engine operating conditions are right, the powertrain control module (PCM) starts the diagnostic using a water temperature counter. The coolant temperature counter times how long the cooling system takes to reach 75°C (167°F). If the coolant temperature to reach 75°C (167°F) within the predetermined diagnostic window, this DTC will set.