So I've been having issues with my EGT sensors for about two months now. I started by replacing the maroon passenger's side EGT sensor because that was the only one that was acting up according to VAG. No problem. It was pretty easy to fix.

Shortly there after, I rescanned and found that BOTH EGT sensors had problems - both had a short to ground. I find this quite odd that now both sensors are either dead or acting up.

I went into the dealership about three weeks ago for inspection and of course they wanted to change both right away because "they must be changed in pairs" according to Audi. I told them to hold off on doing that because I wasn't convinced that simply replacing BOTH sensors would even take care of the issue in the first place.

My question is what could be contributing to both sensors going bad at the same time? Do these sensors share a common ground that I could have some how cut / damaged when I replaced my secondary air pump? I ask this because I noticed that right below where the pump sits there is a good amount of wiring. I suppose if I knocked a wire out of place, I could have pinned it against the block or an exhaust component, causing it to melt.

Any help or pointers with this issue would be greatly appreciated. I'm pretty stumped right now, and am disappointed with how rough the car is running... I miss the power my car had prior to these issues.

BTW, I have a 2003 A6 2.7T.

 

I forgot, here is the latest VAG results:

 

You may know this already, but it's now in limp mode because of the EGT codes. The EGT sensors are actually very sophisticated temperature probes which put out a pulse-width modulated signal proportional to the probe temp between 950C and 1025C. If the ECM doesn't see the pulses, it decides the sensor is malfunctioning and makes the mixture richer, and limits the boost. The sensors usually fail because the wires soldered to the circuit board in the box break off under vibration from the engine. That's why you often get the "intermittant" fault code as the wire only makes contact some of the time.
There are posts on several Audi forums about dealing with this, from replacing them like you did, to how to repair the broken solder joints, to getting a custom flash to make the ECU ignore the signals entirely. I've been working on a way to digitally display the actual temperature in real time from the PWM signal itself (rather than installing separate EGT gauges).
Unfortunately, the replacement units seem to fail quite often. I've seen several people claim that when they re-solder the wires in the box they never have another problem. I find it hard to believe that Audi can't make these units more rugged, but maybe they have a warehouse full of the old ones to get rid of...
Having them both go bad at once is a little suspicious. I'd look to a bad connection, possibly like you suggest in the ground feeding the sensors. Maybe check both connectors to make sure there's no corrosion in them. According to the wiring diagram in ELSA (factory online manual system) the power to the sensors is from the same source that runs a lot of the sensors and solenoids in the engine compartment, so if the fuse for that was blown, you'd get lots of other codes (if it would even run). However, they do both share a common ground, listed as "Ground connection -1- in engine compartment wiring harness" so your thought there may be exactly right. It should be a green/yellow wire, btw.
Unless you want to get a flash that ignores them, you don't have any choice but to get them working again. I have seen one post where the owner connected the signal from a good working unit to the ECU wiring for both banks, fooling the ECU but thereby only monitoring one side of the engine. I'd say if you push the engine hard, you should have them working - the sensors are a lot cheaper than a pair of turbos or a new engine.
Jim

 

Having a similar issue with my 2003 2.7T Allroad and could use some team problem solving. I have already tried re-soldering both EGTs (as suggested in other forums) to no avail.

Faults as follows:

17866 - Exhaust Gas Temp Sensor 2 (G236)
P1458 - 35-10 - Short to Ground - Intermittent
17862 - Exhaust Gas Temp Sensor 1 (G235)
P1454 - 35-10 - Short to Ground - Intermittent
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-10 - - Intermittent
16688 - Cylinder 4
P0304 - 35-10 - Misfire Detected - Intermittent
16689 - Cylinder 5
P0305 - 35-10 - Misfire Detected - Intermittent
17869 - Exhaust Gas Temp Regulation for Bank 1
P1461 - 35-10 - Implausible Signal - Intermittent
16690 - Cylinder 6
P0306 - 35-10 - Misfire Detected - Intermittent
17831 - Secondary Air Injection System; Bank 1
P1423 - 35-00 - Insufficient Flow
17819 - Secondary Air Injection System; Bank 2
P1411 - 35-00 - Insufficient Flow

I am assuming the misfires are a result of the faulty EGT signals, so I'm really focussing on fixing these. I'm suspicious of the fact that both are giving intermittent short to ground and wonder if there's a common cause other than both of them failing. What else can I check?!

 

I finally fixed my EGT sensor issue(s) by REALLY scraping away at the silicone in the sensors and making sure I had a really GOOD contact between the pin and the board. It took me several attempts, so you maybe in the same boat. I thought I had a good solder connection but I didn't.

 

I will try again with a more rigorous bench test (maybe this will help http://www.rst-engr.com/rst/articles/egtcht.pdf) to see if I've actually made a difference before putting them back in the car.

 

I suppose if you get your hands on a decent multimeter you could check for continuity as that is normally what happens with the EGTs on our 2.7Ts - There is no longer continuity between the probe and the ECU, so the car goes into 'safe mode' to protect itself. You could go through what that PDF outlines, but that might be a little overkill with what is likely wrong with your EGT sensors. I would try a simple continuity / resistance test first then go from there.

Though, it is odd that BOTH are acting up at the same time. Then again, I did have to re-solder both of mine at one point or another, so it isn't a huge surprise.

 

Just a note on the OEM Audi sensors. The dealer is correct, they must be replaced in pairs. The reason is, the replacement sensors are different and if you only replace one it will "read" different from the remaining original and set a code(s) and/or put the car into limp-in mode again. If the ECM sees implausible signals (signals in range but that don't make sense) it'll go into limp just in case. Basically, it will see different temps for each side for no obvious reason (like a misfire, an A/F ratio problem, etc) and that's called "implausible".

 

Yesterday I did a test drive with the vag com to see what it's actually reading and they both seem to be stuck at 945C no matter how high I get the RPMs. So it's not an implausible signal but it is just assuming the lowest possible temperature reading on both sides.

I voltage tested the car side of the wiring harness with the ignition on and found reasonable readings, so I'm thinking it is actually 2 busted EGTs. Considering the amount of problems people have had with these, I'm not actually that surprised anymore.

I will remove the passenger side EGT tonight (since it's a lot easier) and re-solder again to see if I can get it to read. If that works, I'll do the other side. Else, I'll replace them completely.

 

No progress on this. It's too cold in Calgary to work on the car without a garage