Audi Thermostat May Be Faulty
This bulletin applies to 2017-2020 Audi A4, 2020 Q7, 2019-2020 Q8, and 2018-2020 A6/A7 vehicles. The MIL may be on and the fan may be running permanently.
At least two DTCs may be stored in the ECM, including P218100 (fault in cooling system), P017B00 (sensor for cylinder head temperature implausible signal), P308100 (engine temperature too low) and/or P01E400 (sender 3 for coolant temperature implausible signal).
Remove the thermostat and check whether it closes completely. If the coolant is still warm, put the thermostat in cold water to restore its original condition.
If there is a gap between the chamber and seal, the thermostat is faulty.