Exhaust gas temp sensor?

[S4INT]

Apart from the obvious, what does this do and how important is it that I replace it?

Came up as a fault on VAG-COM a few weeks ago but until today haven't noticed any problems with performance. Felt a bit sluggish on full throttle today, but could have been the heat?

Any advice would be welcome!

[Morpheous]

If you have acrobat reader, send me your email and I will send you the 2.7 self study guide, everyting is explained within.
I have one of these sensors for sale on ebay, there are two, mine is for bank 1. Cyls 1~3.
Check out the link

http://search.ebay.co.uk/_W0QQsassZwngcdrbader

[Wak]

There's only 1 on a BAM TT and if it goes you can have the ecu cutting power and erratic behaviour .

if it underreads you could be stressing the engine, if its overreading then it could cut power as well. Symptoms are similar to maf degredation.

[Imolavirus]

the EGT simply measures the temp of the exhaust gas before it enters the turbine housing. It is located in the flange on the exhaust manifold that bolts to the turbine housing on the turbo.

Like the others said a failing/failed EGT sensor can cause weird behavior as well as decreased performance. The EGT is used in adjusting afr's relative to the temp of the exhaust gas so a malfunctioning sensor can cause issues there.

Replacing it is not too bad depending on which side it is. Bank 1 (passenger side) is a lot easier than Bank 2 (drivers side). The main battle is getting the heat shield on the downpipe out of the way enough to get to the EGT sensor.

[Morpheous]

You got a left hand drive car then?
Bank 1 is cylinders 1~3, bank 2 is cylinders 4~6.

If the sensor malfunctions, it can't determine the temperature in the exhaust.
As the temp rises above 950 C it will richen the mixture to cool things down.

Never seen one of these sensors on a TT, it does however have two O2 sensors.

[Wak]

Never seen one of these sensors on a TT, it does however have two O2 sensors.

Here's the puppy...on a TT
225 BAM engine only, so later S3's should have one
http://www.wak-tt.com/egt/egt.htm

The centre arrow is the control box for it


I only found out after 3 years of ownership recently

[Morpheous]

You got a part number for it? may be the same as mine, could sell it to TT owners too.

[tartan_rob]

The part on the TT does not look the same as fitted to the S4. The s4 has a long probe (l-shaped) and a copper nut to hold firm onto the exhaust. The wires are shrouded in metal braid and go into a control unit that a multiplug connects into it. Both left and right bank on the S4 are the same partnumber and both (I think) are located AFTER the turbo, left bank about 1/2 foot down the downpipe, right bank, immediately after the turbo. If the code still exists your performance (and fuel economy) will be gubbed. You notice this when you change it. They are about £120 from Audi and if they are gone they should be changed. Would you drive without Lambda sensors working properly...?

[Imolavirus]

Morpheous-
I do have a left hand drive car Also on the TT's, the lastest of the 225TT's have the EGT sensor in the turbine housing. There were two different K04's used on the TT, the K04-20 and K04-23. The K04-23 used in the later model 225TT's has an EGT bung in the side of the turbine housing.

Tartan Rob-
The EGT sensors are located before the turbos, in the flange on the exhaust manifold.

[tartan_rob]

ImolaVirus, possibly on the right bank but not on the left bank. I'll take a photo and post it.

[S4INT]

Thanks for the info and replies guys, but I'm a bit confused as although the sensor is throwing up a fault code, the car seems to be running fine at the moment, does it actually need both to be working or can it take the temperature from one side only?

Morpheous - thanks, I'll PM you my e-mail address - the study guide would be useful!

[Morpheous]

Sent you the self study. hope your not on dial up!

I had a problem a few years ago with my S4 and one of these sensors on a trip to France, they only start to be of use when you have been under full load for about twenty seconds, there is a MVB so you can see the temps of bank 1 and 2 and the % of enrichment.
If you scroll through the MVB look for two 950 C readings, these wont move until you are under the above conditions, one of mine shot upto 1300 C, the other increased very slowly.
When working, they should increase steadily at the same rate.
Vag Com would be very useful, a 5052 on the seat with no means of freezing the readout aint funny at those speeds.

If it were my car, I would reduce the load and drive a bit slower until you identify the fault.
No, the reason for two sensors is you could be in a situation where one side has an ignition or turbo problem etc, the ecu needs to know what is going on so if one side does run too hot it can take precautions to help save the engine, the self study explains it better.

[Imolavirus]

ImolaVirus, possibly on the right bank but not on the left bank. I'll take a photo and post it.

Both sides are like this pic......it's mounted in the exhaust manifold flange

[Turbo Joe]

Recently one of the Exhaust Gas Temperature Sensors went on my S4 twin turbo(B5). Recently the technics at Audi have modified this part and not informed anybody about the change.Ref new part number to old part number.
078919529D-Original part for S4 and RS4.
078919529F-New Modified Part.
As we can see the prefix 'D' has been changed to an 'F' but thats isnt all that has changed. This new prefix 'F' part is less tolerant to high temperatures than the old and a limiter programmed into the sensor reduces performance by 10-15%.Ie modified S4-330bhp, down to 300bhp and standard RS4-380bhp down to 342-345bhp and trust me you can feel the difference from the original part. If you can hunt down the old part, my advice is do that unless the power drop doesn't really bother you.

Additional Info: 1 theory to over come this if you have no choice but to use the new modified "F" part is to change the sensor over, clear the fault codes but don't and I mean do not set the learn valves back to basic settings. Therefore the car will still operate under the original "D" settings instead of the New "F" sets. I was mocked when I posted this information before by folks who have had theirs changed and didn't notice a difference. With them, the learn valves on their vehicles probably remained untouched so they retained the old data and thus the original power. My suggestion is if you can, get a reputable garage to change it outside Audi so your learn valve settings won't be reset.

[Morpheous]

Bollox, the ecu learned values are for throttle position ignition knock map and fuel trim, this is an input sensor. The learned value wont change how this sensor operates so what your saying is there is no change with the sensor! if deleting learned values it will be ok.
Kim (QST) had mine upto 330 on a special stage 1 from MTM with F type fitted.
RS6 use same sensor, does that feel flat to anyone???

This sensor is supplied by the parts as a supersession, as only one of these goes down at a time, do you think audi would allow one modified part to be fitted to the car when the other is still the origional?? They make you change both turbos as a pair!! and allow only one of these to be changed?