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The Engine Coolant Temperature (ECT) sensor is located in the coolantpassage of the cylinder head. The ECT sensor is a variable resistor whoseresistance changes as the temperature of the engine coolant flowing past thesensor changes. When coolant temperature is low, sensor resistance is high;when coolant temperature is high, sensor resistance is low.

The Engine Control Module (ECM) checks ECT sensor voltage and uses theinformation to adjust fuel injector pulse width and ignition timing. Whenthe temperature sensed is very cold, the ECM enriches the fuel mixture andadvances ignition timing. As coolant temperature rises, the ECM reduces theamount of enrichment and timing advance.

The ECM will set P0116 and the Malfunction Indicator Lamp (MIL) willturn on if the ECT sensor's actual performance curvefalls more than 68?(20?) below the ECM's model curve (based on fuel delivery, ambient air temperature and engine running time) for 0.2 seconds during two driving cycles. This code indicates uncharacteristic engine temperature performance being read by the ECT sensor or ECM.

The ECM will set P0117 and the Malfunction Indicator Lamp (MIL) willturn on if the ECT sensor reports a temperature below -49?(-45?)for 0.2 seconds during two driving cycles. The ECM will set P0118 and theMalfunction Indicator Lamp (MIL) will turn on if the ECT sensor reports atemperature above 284?(140?) for 0.2 seconds during two driving cycles.