Circuit/System Description

The exhaust gas temperature sensors are variable resistors that measure the temperature of the exhaust gas. The Engine Control Module (ECM) supplies a 5 V bias to the exhaust gas temperature sensor (EGT) signal circuit and supplies a ground to the low reference circuit. When the EGR temperature sensor is cold, the sensor resistance is high. When the EGR temperature increases, the sensor resistance decreases. With high sensor resistance, the ECM detects a higher voltage on the EGR temperature signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the EGR temperature signal circuit. After an 8 hour engine off soak time, the power up temperature of the exhaust gas temperature sensors are compared to the engine coolant temperature sensor (ECT) to determine if the temperature is plausible.

The following table illustrates the relationship between the temperature of the exhaust gas, and the resistance and voltage seen at the EGT sensor.