A recent VAG scan indicated that EGT Sensor 2 had failed on my S4.
Talking with a few techs and STFA indicated that this was really no big deal so long as Sensor 1 continued to function. The car, however, seemed to be operating in less than an ideal state.
While WOT seemed OK, the mild acceleration around town and using the throttle between 0-1/2 seemed less than perfect. I mean, it wasn't terrible, but the car just was not quite as smooth as it should have been.
Anyway, I'm very particular about my car (as any S4 owner should be) and I opted to change out the sensor, even though some seemed to think it was a waste of ~$200.
If this had been sensor #1, it would be no big deal, as that is readily accessible from the top of the engine bay - on the passenger side.
Unfortunately for me, this was sensor #2, which you have to get from down below - and it is TIGHT!
In-case anyone needs to do this, here's how I ultimately succeeded in removing the sensor. Of-course, follow these directions at your own risk.
* Lift the car up safely (meaning, use jack stands, not just a jack!)
* Remove belly pan
* ensure area under car is well lit.
* locate sensor (see the pic).
* Unscrew sensor. Now, that will be fairly difficult. I initially tried getting in there with an open end wrench. I was able to move the nut, but only about 1/16th turn at a time. I decided that this was not the way to go.
* Since that plan did not work out well, I cut the sensor, such that I could use a 3/8's drive 17mm socket. Because space is at a premium, only the U-joint type socket would fit.
* After getting the nut loose with the socket, remove it, and take the nut off by hand.
* Go top side, and remove the plastic cover to the right side of the silver air duct and disconnect the retainer catch. (not completely necessary, but it makes things easier). The sensor is toward the back. It is a black rectangle with a braided line attached.
* A deep 10MM 1/4 inch socket can be used to remove the sensor. Note that on the driver side of the sensor, there is a nut holding a ground wire, as well as a stud which need to be removed. Note the orientation of the stud for proper re-installation.
* Once disconnected, pull the sensor out, noting how the EGT wire was run to the down-pipe. Install the new sensor, ensuring that you run the braided cable to the down pipe the same way the previous one was removed.
* Replace plastics and retainer catch.
* Back under the car - insert the EGT probe into the down-pipe and tighten.
* Ensuring the engine bay is clear - start car, scan with VAG, the code should change from 'no signal' to 'intermittent'. Clear codes. If no code is found at this point, test drive
After changing this sensor, the car is again smooth. If you have a sensor which has failed, replace it!
Here are some pictures to help out if nessessary. Sorry the text in the images isn't so good... what did you want for free