P3028 - 008 - Implausible Signal
 

Where do I start......

I've been a bit quiet the last few months as I've been quite overwhelmed with work and the majority of my cars all having niggling, expensive and hard to diagnose faults. Both my v10's have been off the road now for most of this year and I was really getting to the end of my tether with it all to be honest.

But this post is a positive one, as I seem to have a solution for a problem that is so far undocumented anywhere in the known universe, and my god have I googled the **** off it ;)

So, a 2010 RS6. Remapped, and with Miltek to add a little extra complication, and had a large number of other niggles, and poor tyres and worn brakes and basically it was a blown fuse short of a write off some weekends I'll tell you.

It drove almost perfectly when I got it. Very hard to fault it, but due to a large number of other issues to deal with, it spent a lot of time sat and at some point it just became obvious that it was very not right.

The symptoms were simple. Drive it like a saint and all seemed well. Drive it like an RS6 and it would crap out at the most inopportune moment, ESP/engine warning lights, limp mode, violent deceleration and you basically look like a knob in an Audi who can't manage to overtake a fiesta successfully.

The error that was a constant was:


012328 - Angle Sensor 2 for Throttle Drive 2 (G298)
P3028 - 008 - Implausible Signal
Freeze Frame:
Fault Status: 01101000
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 108134 km
Time Indication: 0
Date: 2017.07.25
Time: 15:22:42
Freeze Frame:
RPM: 5061 /min
Load: 14.1 %
Speed: 81.0 km/h
Temperature: 82.0°C
Temperature: 50.0°C
Absolute Pres.: 1000.0 mbar
Voltage: 13.335 V

Ignition off and back on, and all was sweet again. Until you put the throttle down.

Every single piece of advice under the sun will tell you to change the £1000 throttle bodies. Or clean them. Or do a rain dance around them. Or polish them or basically just keep messing with them indefinitely until it works. Ignore it. The throttle bodies are perfect. All 5 of the ones I fitted over the time... :rolleyes:

I spent countless weekends driving like a fairy for 20 mins to warm it up, then like a pillock trying to figure out what the actual root trigger was.

And about a month ago, I nailed it. Reproduced it time and time and time again. I was so happy, in a weird way.

I found I could drive any way I wanted in 3rd, 4th, 5th and 6th gear - but - in 1st or second hard boost over ~3500 rpm and it would crap out. Every single time.

It is no co-incidence that this is the time that the throttle bodies are moving their fastest to alter the inbound flow of air. In every other gear, the revs build a bit slower, so no sudden swing.

The throttle bodies (2 of, 1 per bank) are the simplest contraptions ever. They have 6 wires. 2 wires are DC voltage to the flap motor that moves the flap backwards and forward to increase/decrease air.

Then, there are 2 pairs of wires. Each pair goes to a position sensor, exactly like the accelerator pedal. One sensor reads high and reduces with movement. One sensor reads low and increases with movement, hence the sum of both sensors must be same give or take a particular tolerance.

So, if its complaining at the readings, lets see the readings. Here is a good working example from ECU1, reading throttle body 1 using vagcom on turbo mode. You can see when the throttle is blipped the sensor readings invert with perfect precision.

http://forum.a8parts.co.uk/attachmen...1&d=1507363990


Now, look at the graph for ECU 2:

http://forum.a8parts.co.uk/attachmen...1&d=1507363990


So, circled in yellow is the problem. They simply don't match. The ECU thinks that the value is considerably different to the other sensor, and freaks out....

Now, if that wasn't weird enough. Check out this graph. Sorry for the noise, but look at the pink and brown lines.

http://forum.a8parts.co.uk/attachmen...1&d=1507363990

According the ECU, the value is over 100%... wtf. So its reading more voltage in, than its sending out. huh ?

At this point, I struck up conversation with Doug at MRC as I was trying to understand if the remap in any way could affect the measuring blocks. I wasn't sure what response to expect from my detailed DIY self diagnosis email as I'm sure they're busy guys, but to their credit he engaged with me and suggested as throttle bodies had been changed, first port of call was to swap out the ECU just to make sure.

Its worth knowing that MRC can clone ECU's, so forget key coding and immobilisers and all that jazz, they just hoover the entire config and blat it over. Very handy.

Before that though, Doug had spotted that the signal on sensor 2 showed irregularities on idle. This was another major breakthrough as no longer did it have to be warmed up and then driven quickly to diagnose. This was the car wobbling a bit on idle at their workshop:

http://forum.a8parts.co.uk/attachmen...1&d=1507363990


Good, easy to reproduce, but sadly the ECU swap made no difference. On the plus side, @ £1500 i was sort of glad tbh.

I had personally changed both throttle bodies. Cleaned them. Stripped them and cleaned them. Swapped the sides over, and then Doug also swapped them over again to rule it out, but never, ever did the fault move.

So, the final, and least likely culprit is the wiring. Its a perfectly intact, unmolested beautifully looking loom, so it made no sense - but - I did find that the VW Tourag had an Technical Service Bulletin out regarding a similar issue that suggested that the connector on the Throttle body, having only 6 wires, was prone to a bit of movement and could over time cause problems.

I had previously questioned Audi on TSB's for the V10. Nothing. Spoken to independent Audi specialist, not ever heard of a V10 issue. It was new to MRC also, and to suggest changing the 6 pin plug and the wires back towards the ECU seemed rather odd, but having literally eliminated everything else I authorised the works.

A few days later I got another screenshot:

http://forum.a8parts.co.uk/attachmen...1&d=1507363990


It seems fixed came the message, but as they'd also serviced it and found the inner edges of the front tyres to be bald they could no longer road test it.

Aargh. How frustrating :rolleyes:

So, Finally, today got it trailered home and I am abso-fecking-lotely chuffed to report it is now spot on.....

I thought it would be, but the proof was in the pudding. Interesting it had a dyno session whilst it was there and posted up virtually identical numbers to 3 years ago, which was a bloody good sign.

Its also drives a bit smoother, and the exhaust doesn't pop quite as much as presumably the fuel/air mix is now spot on. I'd say gear changes are even sweeter too........

Hurrah.

So, quite a trek to drop it off at MRC but it was worth the effort.

Now for a set of new brakes and an MOT and we're about there on this one. ..... I now have a full 750 bhp just in time for winter. Oh goody.... :D

So chuffed in fact that you forgot to include the images +++

No, sadly like everything else with this car, if it can go wrong it will..... ;)

I didn't forget the images, I actually forgot to submit the post....

I realised many hours later and almost unbelievably, did enough 'backs' on Internet Explorer to find the last preview I had, and was able to submit it..... but my laptop had cached the images so didn't realise it had lost the photos... !

I've done the same many times, there's something about the way this forum software behaves that makes it easy to forget you're still editing/revising/previewing a post and then just do something else and lose it.

More than once I've gone back to look for something I'd posted and ended up convinced that the forum had "lost" it. Eventually realising that I'd just never actually posted it in the first place! :o

Though the way Microsoft software works does make such slips easier. :tuttut:

Excellent. Love it when things get sorted, especially the annoyingly (possibly) expensive kind.

So having replaced the connector (and by the sound of it a length of loom leading to it) was there any detailed examination to see what had failed?

Things that spring to my (relatively inexperienced) mind would be:
- Contamination/corrosion in the connector(s) that mate to the throttle body.
- Wear/looseness in these connectors.
- Poor contact between the cable core and the connector due to manufacturing problems or wear.
- Connector insecure in the plug body.
- Failure in a cable core.

I'm sure there are other things to look for as well.

I too would love to know the forensics on the cause, dirty contacts can explain variable readings but can't explain the >100% values unless there was shorting between pins.

On another note, how did you decide to remedy the brake situation?

With hindisight, perhaps I should have asked for the old bits they removed, but to be honest its been quite a chew on to manage the operation long distance as it is with everything else going on.

My strong suspicion is that the cable core had a number of frayed strands where it 90 degree bends towards the throttle body.

The connectors and pins had been thoroughly inspected and cleaned several times....

I picked up a full set of steel callipers, with < 300 mile new front steel discs. I had already dropped a set of brand new steels on the rear as they are the same fitment.

The 'cheapest' I've managed to source a full set of ceramics is about £6500. There is also some doubt how bad the front ones are. Audi say they're due, MRC say they look ok.

Until I get them off and weigh them I won't really know.

Ceramics look dam pretty, but for my driving style, I just don't need them, and ultimately for resale, I wonder if having ceramics puts people off so it seems almost certain steels the route that will be taken......