The EGR temperature sensor detects temperature changes in the EGR passage way. WHen the EGR valve opens, hot exhaust gases flow, and the temperature in the passagew ay changes. The EGR temperature sensor is a thermistor that modigies a voltage singal sent form the ECM. This modified singal then returns to the ECM as an input singal. As the temperature increaes, EGR tempertures sensor resisntance decreaes. This sensor is not used to control the egine syste. it is used only for the on board diganosis.