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Home >> GMC >> 2018 >> Acadia Denali, FWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 89 (Engine Controls And Fuel - 3.6L (LF4 LGX) - DTC P0121 LF4 To DTC P0685 LF4) >> Diagnostic Information and Procedures >> DTC P0128: Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature (LGX) >> Circuit/System Description

Circuit/System Description

WARNING: This page is about a different car, the 2016 Cadillac ATS. However, it is still accessible from the selected car via links, so may be relevant.

The purpose of this diagnostic is to analyze the performance of the thermostat, by using the ECT sensor to determine if the engine coolant will increase at the correct rate, and also meet the calibrated target temperatures under various operating conditions. The ECM uses the start-up ECT and the start-up intake air temperature (IAT) to begin the diagnostic calculation. The air flow into the engine is accumulated , and vehicle speed, distance, and engine run time are also factored in to determine if the ECT does increase normally and reach the calibrated target temperatures.

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