The 2.8l V6 engine (both AHA and ATQ) have a temperature sensor attached to the hard coolant line that crosses from the passenger side head to the driver's side head below the throttle body. This sensor feeds information to the ECU, as well as the dash for the temperaure gauge.

The position of the sensor is closer to the passenger side head (it's almost below the cam chain tensioner harness).



Of course, it's not just as easy as opening the hood and changing this piece. Being that it's down low on the back of the engine, there are things that you'll need to remove first.

Start by removing the engine trim cover, and the trim for the airbox lid. Remove the intake hose from the airbox and the hard intake duct.

Next, remove the 10mm bolt from the top of the intake duct, and the harness for the intake temp sensor. There are 2 tricky steps on removing the intake duct from the throttle body. I'm sure replacing the coolant temperature sensor can be done with the intake duct in place, but removing it makes it easiser.



Tricky step one is removing the PCV hose from the driver's side of the intake duct. Squeeze the clips together and slide it off. This is easier said than done. I use long forceps, or a pair of screwdrivers in a chopstick arrangement to do this as my hands are too large to fit down in the area where this connection lives. Once you get the PCV hose removed, proceed to step 2.

Tricky step 2 is removing the bolt that holds the intake duct to the throttle body. There is only one, and it's on the driver's side top of the duct. it's an Allen, the I believe it's a 6mm. I use a 1/4 socket and very short extension or palm ratchet on these once broken free. Have your LONG magnetic probe handy for when you drop things. Not if, when. On the A4, the gap between the engine and firewall is about 2 inches. On an A6, there's a lot more room to work.

Once you have the bolt, the PCV hose, and the IAT sensor connector off of the intake duct, you can pull it off of the throttle body. Now is a GREAT time to clean the throttle body by the way.



As you can see, having that intake duct out of the way makes it a lot easier.

Now, using a screw driver, GENTLY pry the green clip off of the sensor, and pull the sensor and O-ring out of the hole. Clean any dirt out of the hole, insert the new O-ring and sensor, and start putting everythign back together. Make sure that the car is at cold temperature. Remove, and then re-attach the expansion tank cover. This will remove any pressure, and hopefully put the system under a bit of a vacuum, so that when you remove the sensor, the coolant doesn't gush out. When i did this on my car, I did not lose one drop of coolant from this hole, nor did this introduce any air into the system.