AudiWorld Tech Articles

Tech Article Title	Author	Date
EGT Sensor Swap	Steve Trac	2005

W00T!!!! $400 and a couple hours later my car is finally running strong again!!! For several weeks, I have had 2 bad EGT sensors. If I gave the car any boost, it would start to go and then almost buck and cut boost. I found the following DTCs during the last couple weeks and even threw a CEL the day of the CT S4 meet:

17866 - Exhaust Gas Temp Sensor 2 (G236): Short to Ground
P1458 - 35-10 - - - Intermittent

17867 - Exhaust Gas Temp Sensor 2 (G236): Implausible Signal
P1459 - 35-10 - - - Intermittent

17869 - Exhaust Gas Temp Regulation for Bank 1: Implausible Signal
P1461 - 35-10 - - - Intermittent

So I ordered a new sensor from ECS but they don't specify left or right so I waited for it to arrive so that I could get the other sensor from a local dealership.

They are side specific but I read in the archives that you can shave down part of the plastic on one to make it fit universally. The only problem with doing that is that on my car, they fit back to back and share the same threaded bolts. If you had two of the same, you'd have to find another way to secure the boxes. Here are the left and right sensors. As you can see, they're keyed a little different:

Here they are on my 2001.5 S4. As you can see, they're located just to the right of the N75 valve:

Close-up: (the T-fitting is for my Piggie MBC)

I think the location is different on different year cars as well as manual vs. tiptronic. As per Wilson94t's Sensor #2 Install post, he shows his driver side sensor on the right side of the engine:

The Bentley manual also shows then on opposite sides with the following text:
"For vehicles with manual transmission, the control modules for exhaust gas temperature are at rear of intake manifold, on left and right.

Additionally, the part numbers have changed since I got my car:

Original part numbers:
078 919 529D (drivers side)
078 919 529E (passenger side)

New part numbers:
078 919 529F (drivers side)
078 919 529G (passenger side)

Here is the old and new passenger side sensor boxes:

The only other parts you'll need for this install are new hose clamps for the rubber boots that the Y-pipe fits into. The factory parts are use-once. I picked up a couple 52mm-75mm adjustable clamps. Although the new ones are wider than the OEM ones, and don't fit in the grooves in the boots, they still work fine as this part of the engine is not pressurized. Here are pics of the new clamps:

Anyway, to install the new sensors, you need to remove the intake Y-pipe. There are (3) 10mm nuts to remove, the OEM hose clamps into the rubber boots, the accordion hose and that thing connected on the right side. After removing it, make sure you stuff some rags in the rubber boots so that nothing falls in them. Removing the accordion hose makes it a lot easier to work in that area. For those with M-box ECUs, there is a drain plug attached to the bottom of the accordion. It makes it MUCH easier to reinstall the drain if you lube it up (I used spit). Otherwise, it's a PITA to get back in.

On my car and because the sensor boxes are next to each other, there are (2) 10mm nuts to remove to take them out. Be very careful not to drop these as you'll probably lose them in your engine!!

The passenger side sensor is very easy to get to and remove. You'll just need a 17mm box wrench. It's located behind and underneath the MAF housing:

Close up:

When removing it, note the path of the wire so that you can install the new one the same way. Once removed, just replace it with the new sensor.

The driver side sensor is a PITA because you can't access the sensor from the top of the engine. You need to jack the car up on jack stands, remove the belly pan and reach way up to get to it. It's just about attached to the turbo housing and there is NO room to work. I was able to loosen it a little with a wrench and then do the rest by hand. Again, note the path of the wire and remove it. Installation is the reverse of removal. Here's a pic from Wilson94t's writeup. I didn't need to cut anything to remove it though:

Once they're installed, bolt the boxes to the engine with the 10mm nuts. Reinstall the Y-pipe with the new hose clamps and put everything back together. Clear your codes, go for a drive and enjoy your power again.

Here are the old and new sensors for comparison. The old one is on top obviously:

I would never have known what was wrong without a VAG. Big thanks to Uwe at Ross-tech for making such an awesome tool that is affordable and indispensable for anyone serious about their car. A VAG is something most people don't think to buy, or something that they don't need, but I recommend that EVERYONE get one. It's cheaper than most other mods for the car and it will tell you what's wrong if you're having problems.

As I'm out of warranty, I called my two local dealers to see if EGT sensors were covered under the NJ 8 year/80,000 mile exhaust warranty. Both said NO and that only cats were covered. If you can get your dealer to replaces these under warranty, do it and save yourself $400. If they won't do it, buy the parts and install them yourself. They're really not that hard to replace. On a scale of 1 to 10 for difficulty, I give the passenger side a 3 and the driver side a 7 just because there's no room to work.