The OBDII fault code P0544 shows a malfunction in the Exhaust Gas Temperature (EGT) sensor circuit. This sensor protects the Catalytic Converter (TWC) from heat damage.
This sensor is a heat-sensitive resistor. It turns the exhaust temperature into a voltage signal. Then, it sends it to the vehicle’s computer. It has 5 volts of reference, which the computer sends by itself.
When the exhaust temperature is high, the resistance to the ground decreases. But if the temperature level is low, the resistance increases, and there is low voltage. If low voltage is found in the engine, the PCM (Powertrain Control Module) changes the engine timing or fuel ratio to keep the temperature in a range suitable for the TWC.
If the EGT Sensor voltage readings are greater than the limit set by the manufacturer, this code will be set and the Check Engine light will light up.