Circuit/System Description

WARNING: This page is about a different car, the 2017 Cadillac ATS. However, it is still accessible from the selected car via links, so may be relevant.

The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5V to the ECT sensor signal circuit and a ground for the low reference circuit.

The purpose of this diagnostic is to determine if the input from the ECT sensor is skewed warmer or colder than the Intake Air Temperature (IAT) sensor and Radiator Coolant Temperature (RCT) sensor. The internal clock of the ECM will record the amount of time the engine is OFF. If the required engine OFF time is met at start-up, the ECM will compare temperatures between the ECT, IAT, and RCT sensors.

If the ECM detects that the temperature difference between the ECT, IAT, and RCT sensors is not within an acceptable operating range, the ECM will continue to run this diagnostic to determine if a block heater was active during the engine OFF time.