EGR Temperature Sensor: Description and Operation

EGR Temperature Sensor:

All vehicles sold in Calif. and some vehicles manufactured for sale in other states and Canada are equipped with an EGR emission control system. The signal from the EGR temperature sensor is used for vehicle self diagnosis of the EGR system.
The EGR temperature sensor, threaded directly into the body of the EGR valve, is a thermistor with a negative temperature coefficient. As temperature of the sensor increases, its electrical resistance decreases. The EGR system operates only when the coolant temperature is greater than 122~F (50~C).

SELF DIAGNOSIS
The fuel control ECU compares the signals from the EGR temperature sensor and the coolant temperature sensor. If the ECU senses a coolant temperature sufficient for EGR operation, but the EGR temperature sensor indicates a temperature lower than the engine coolant temperature, then a fault code is stored for the EGR valve. If the sensor or circuit is shorted to ground, the ECU interprets the signal as a very low temperature indication and sets a fault code. The ECU will also recognize an open sensor or sensor circuit. The signal from this sensor is used solely for self diagnosis of the EGR valve. There is no substitute signal for this device. If the EGR temperature sensor or circuit fails, causing constant high resistance or open circuit, a fault code will be stored. The ECU does not distinguish between the different possible malfunctions of the EGR sensor. The same fault code is stored for an EGR system malfunction regardless of the actual fault.