Misreading outside temperature sensor on 2001 Audi A4

There are four sensors for ambient tempurature and they work in unison to provide information to the temp reading on the dash, the heater control head ( where to direct air, blending of warm/cold/outside/inside air flapper controls) depending on the ambient temp and the inside air temp sensor located just above the radio as well as the sun sensor on the top of the dash as well as the a/c compressor head.

When you start your car, the body control module takes the readings from all sensors, outside air temp located in front of the radiator, air temp sensor located in the airbox ( senses temp of air being drawn in from the outside into the air box), coolant temp, inside air temp sensor and the sun sensor on top of the dash (this is why it takes a few seconds for the climate control system to begine when you start the car). The intake air sensor is 1st priority, inside air second, coolant third, ambient 4th and sun 5th. For instance, if the sun sensor reads the sun is hot but the interior sensor reads cold, the inside akes priority. The goal is for the system to achieve a tempurature inside the car that matches the selected temp. It uses all of the sensors to set the system up to achieve that goal as quickly as possible.

Example; Its mid afternoon, sunny and 40 degrees outside adn your in stop and go traffic. The intake sensor reads 40 degrees, the outside sensor reads 60 degrees (heat from radiator...engine heat protrudes into cabin) and the sun sensor reads high (sun is strong). The system is set for 72. priority one sensor reads 40, inside sensor reads 65, ambient reads 60= system will blow hot air to the floor out put, dash outlets will lightly flow 65 degree air so the sun doesnt roast you yet your feet are cold(if it blew hot air from all outlets, your upper body would be hot but your legs/feet would be cold). as the interior sensor reaches desired temp, air will be distrubuted through thee dash, defrost and floor with the warmest air coming out the floor and defrost, coolest air out the dash vents. Its a complex system!

The two sensors that will screw the system up the most are the intake and interior sensors. the system will function reasonably well with just those two sensors though it wont blend air temps between outlets if the sun sensor isnt working. If the outside sensor fails, it simply uses the intake sensor, if the intake sensor fails it will rely on the front sensor. However, since the intake takes priority over the outside sensor, if the intake sensor sends incorrect resistance info rather than failing, it will take priority and cause the unit to malfunction such as in your case.

The intake air sensor can be changed from the outside with patience. If it where me, I would pay the two hrs labor and let the dealer do it right.

Kevin,
Kevins Small Engine service,
South Berwick ME. 03908

Ford has the same problem with their sensor, internally short out or come lose check to make sure it is plugged tightly, if it do a quick visual of the wires and make sure no nicks,cuts in the wire, if nothing can be seen to fix replace the sensor.