90 Quattro 20V (Canada) L5-2309cc 2.3L DOHC (7A) (1989)
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EGR Temperature Sensor: Description and Operation
EGR Temperature Sensor
All vehicles sold in Calif. and some vehicles manufactured after March 1990 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 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 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. 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.
