1991 Audi 90 Quattro EGR Valve Temperature Sensor Replacement Cost

Exhaust gas recirculation systems transfer exhaust from the engine from the exhaust system to the intake manifold. This is in effort to reduce emissions by allowing a more complete burning of fuel and preventing the formation of harmful chemicals. For more efficient operation, some manufacturers program the engine control module (ECM) to use an EGR valve temperature sensor to control the operation of the EGR valve.

The EGR valve temperature sensor will constantly read engine exhaust temperatures to determine if operation of the EGR valve is correct or incorrect. This may be used in place of an EGR valve position sensor so the ECM can monitor if the valve has opened upon request. When the EGR valve is opened, the EGR temperature sensor is heated by hot exhaust gases flowing through the EGR valve. Upon being heated, the EGR temperature sensor will change resistance which creates a voltage change in the signal voltage to the ECM. The ECM will interpret the voltage received from the temperature sensor as the EGR valve being opened or closed.

When the EGR valve temperature sensor fails, the ECM will identify this failure by illuminating the check engine light and storing on-board diagnostic (OBD) fault codes referencing the EGR system or the EGR valve temperature sensor. If the temperature sensor is at fault, this will be the only symptom of the failure in most cases. The worst case scenario is the engine running slightly rough and a decrease in fuel mileage.

While not an emergency, this issue should be repaired at the earliest opportunity. Not only does excess fuel consumption increase the cost to drive, but the additional fuel being pumped into the catalytic converter can cause premature failure.