Allroad "Tank system malfunction"

[Flufy]

A6 C6 Allroad - been on holiday for a week, started up the car to find this error. Car had 1/4 tank of fuel.
Anyone one have any idears on what this may be?
The car is going in to an independant garage Monday to get it checked out but the fault happend during 4 - 5 trips then its been ok since.
25731

[Whippy53]

Sounds like a sender unit fault.

[Flufy]

Sounds like a sender unit fault.

Was thinking the same, had that fault and many others with my last A6 3lt TDI Le Mans, not too bad on the wallet.

[Guest 2]

No point in guessing until a scan is done ;)

[dan2485]

Apologies A6_Chris did not know how the dislike button was pressed removed now.

[gianton]

Had the same, had the sender unit in the tank changed to fix it. My indie said that it's better not to squeeze any fuel in once the hose auto stops.

[MarkTM]

My indie said that it's better not to squeeze any fuel in once the hose auto stops.

Really? So some think overfilling can be the cause of this...how exactly:confused:

[gianton]

Really? So some think overfilling can be the cause of this...how exactly:confused:
I was surprised too, but I do what my indie said. Gas stations stuff always overfill unless you tell them to stop when the hose auto stops.
BTW I had the same issue on my BMW again always overfilled.

[MarkTM]

OK I had the tank repair kit (£28 and have quoted the part no on another thread on here) installed after tank was reading empty, am guessing that an 07 3.0 doesn't have the 'tank error' capability in DIS that the AllRoad does?

I have always overfilled especially before long journey's and can squeeze 85l in if this is done, as purchase 100l (the remainder in jerry cans) as with fuel vouchers can get as low as £1.10 per litre.

The repair was done in 2012 and no issues since then, but am a little sceptical to think that overfill can result in failure.

[Flufy]

Indi said if the fault had not come back then just leave it and if id does then pop back in when the fault shows, car down to 1/4 tank and fault comes back again but i need the car for this weekend so i put £60 fuel in and fault goes away again.
Iam thinking that the system has an issue when the tank is 1/4 full so will have to time it right after this weekend to take it back in.
Thanks for all the replys.

[Splash]

As a rough rule of thumb I use a "safe" range of 500 miles on my C6 3.0 allroad with its 80 litre tank filled to cut-off. The dealer once said that the gauges and ranges on C6 are notoriously inaccurate.

My C7 allroad has a smaller 60 litre tank, but is 10% more efficient so I still use the same 500 mile limit and have got my wife into the habit of resetting the odometer if she refills either (a rare event).

I'm sure you can do more than this quite safely, but I'm allowing for adverse weather conditions and some hold-ups etc. or indeed anything which reduces MPG.

[Splash]

I'm now repatriated with my C6 and was going to look at recalibrating the sender(s) to provide a larger "reserve" to match up with my 500 mile rule-of-thumb (above). I remember seeing a link to to a Russian site that explained something like every 1 point increase made for 1/4 litre difference. After several searches I can't locate the link. Anyone able to help?

[KjetilRos]

I always get this fault when I fuel up at "Statoil-stations". They use 8% biodiesel in the fuel. When I fuel up at Shell I never get the fault. A bit strange, but I have tried it through this summer and fall, and it seems to be correct.

Sorry for the bad English. Im norwegian..

[gianton]

I always get this fault when I fuel up at "Statoil-stations". They use 8% biodiesel in the fuel. When I fuel up at Shell I never get the fault. A bit strange, but I have tried it through this summer and fall, and it seems to be correct.

Sorry for the bad English. Im norwegian..

Strange cause I never get this when using regular diesel (with 8-10% biodiesel) or using Shell V-Power diesel. I think it's either showing this message if the sensor is defective or not showing it at all, no matter what type of fuel used.

[MarkTM]

I'm now repatriated with my C6 and was going to look at recalibrating the sender(s) to provide a larger "reserve" to match up with my 500 mile rule-of-thumb (above). I remember seeing a link to to a Russian site that explained something like every 1 point increase made for 1/4 litre difference. After several searches I can't locate the link. Anyone able to help?

A quick google found this link, does post 9 help in any way?

DIY: Fuel Level Sensor/Sender Replacement (http://www.audizine.com/forum/showthread.php/306327-DIY-Fuel-Level-Sensor-Sender-Replacement)

[KjetilRos]

Strange cause I never get this when using regular diesel (with 8-10% biodiesel) or using Shell V-Power diesel. I think it's either showing this message if the sensor is defective or not showing it at all, no matter what type of fuel used.

I just do not undrestand why it is so on my car. Dont know how to explain it, but the tank sender will probably fail at some point.

[Splash]

A quick google found this link, does post 9 help in any way?

DIY: Fuel Level Sensor/Sender Replacement (http://www.audizine.com/forum/showthread.php/306327-DIY-Fuel-Level-Sensor-Sender-Replacement)Cheers Mark.

That reconciles with roughly what I remember, but although it might alter the needle position, I'm more interested in improving the accuracy on the DIS "range" calculation. My wife put 20 litres in to safely get her to a location she could make use of a fuel discount - the last location before she got here but still 150 miles away from here! Theoretically she would have been on fumes had she made it without the safety stop (she got a further 55 litres in), but there's no consistent way of allowing a reserve of say 70 miles. It seems to vary from one fill to the next.

Maybe the needle position does impact on the calculation? Resetting the odometer works if you remember to do it, but the female brain doesn't think like a bloke's.

[MarkTM]

the female brain doesn't think like a bloke's.

No it's far simpler, they just like to think they are complex :D

[rcw265]

I've not yet got my C6, as I've said in my intro post, but just a thought regarding keeping a safe reserve.

I've found all trip computers to be vague at best regarding range, due to things such as speed, congestion etc. Instead, whatever vehicle I'm driving, I always go by the fuel consumed. I just reset the trip when I fill up and rely on what it tell me I've used, and thus what I have left. I find this far more reliable than remaining distance display.

I know this doesn't help with your calibration issues, but it might help next time your OH or you need to know whether you'll need to top up or not.

[Splash]

Hooked up VCDS to check today. Despite all other references, the range applicable to my allroad isn't as small as about 10 units but a massive 64 (96-160) covering a volume of 8 litres. Given that I'm the first and only owner of the car it was mighty strange to see mine set at 160 - the most optimistic and least conservative setting!

Reset to 128, but will see how that compares with my arbitrary 500 mile range. At least my reserve should be 4 litres more now (I hope).

[gupsterg]

Hi Splash,

Changing adaptation channel 29 / 30 lower in your case will mean fuel level in tank is under read on ins.cluster, so more fuel left in tank in reality and this is if the corrective value of 160 was right in the first place.

From what I read as the quattro cars have 2 sensors you'd need to do adjust 2 channels?

google Audi portal , select Diagnostic , then ECU , from selection box select Audi A6 4F (2005-) and in other selection box 17 | Instrument cluster ,

Then view J285_4F_90_____6_1203_21_Tankgeber1.htm and also J285_4F_90_____7_1203_21_Tankgeber2.htm

You also may find reading J285_4F_90_____45_0204_21_BeschreibungAnpasskanal. htm helpful plus it have some info on channels 31 32 33 which may or may not help you.

Perhaps what I'm suggesting next is not for you but as most owners state DIS over reads MPG why not correct that? then your range/MPG indicator would be more accurate on DIS. I did it by using my fuelly log , Link:- Correcting my DIS through the seasons ... (http://www.vwaudiforum.co.uk/forum/showthread.php?159424-Correcting-my-DIS-through-the-seasons)

ATB
G

PS sorry for the long winded way of stating the audi portal site but as links could be moderated (removed) only way I could post info.

[Splash]

Thanks Gup.

That's indeed the document that I'd seen before although maybe a direct link to a non-quattro model which may now have been removed.

I had a quick look at the subsequent channels after I adjusted Ch30 only because it said Sender 1 and that logically Sender 2 would appear after. Didn't think to look at Ch29!

I've thought about correcting the DIS, but as I have 3 sets of wheels with slightly different radii and characteristics (19" summer, 18" off-road, 17" winter patterns) I've got my head around the quoted DIS figures as being a constant in the equation so to speak, despite sounding like a contradiction. My winters are about 2% oversized, but it's likely that these will remain on until I sell the car. I'll then refit the 7 double spoke (RS4/Le Mans) in either the 19" or 18" (I have both) per the new buyer's preference. I'm keen to leave it as close to stock condition as possible i.e. no mods (incl. DIS), although increased confidence in the "distance to empty" wouldn't go amiss - especially for the new owner on their first long trip.

[Splash]

Had a chance to hook up again today and went to Ch 29. No description - just a value: 137. Decided not to change it.

Clicked on the drop-down menu at the top which shows all the channels (not in order?) and there's only 1 relating to a Tank Sender. Another relates to a refill calibration or similar.

I decided to adjust Ch 30 (Sender 1) to 96 - the opposite end of the range from its setting as I found it. I did notice it uses the word "parallel" in the description so maybe this applies to both senders. Either way at least one of them should be conservative now.

[gupsterg]

The word parallel does not mean it apply to both sender units.

The word parallel is used to describe when sender unit say x fuel adjustment is done in parallel to it by the set value.

Read description of channel 33 on audi portal, that adjustment does not work in parallel.

You may not be getting description for channel 29 as it may not be in VCDS label file.

My educated assumption would be that channel 29 & 30 will be different adjustments due to how its designed to allowed manufacturing difference between reading from sender units? but really don't know :)

[Splash]

Thanks again.

My interpretation of "parallel" is like "pro rata" or linear like a 1:1 gear, whereas the description of Ch 33 implies the "gearing" can change from a 1:1 profile further up the level. I hope you understand my analogy as it sounds muddled when I read it even if I know what I'm thinking.

Will maybe try changing Ch 29 as I can always change it back. I think you're suggesting that the different values for Ch 29 and 30 is a sort of bias adjustment tuned to the different manufacturing variation of each car or variant?

[gupsterg]

My interpretation of "parallel" is like "pro rata" or linear like a 1:1 gear, whereas the description of Ch 33 implies the "gearing" can change from a 1:1 profile further up the level. I hope you understand my analogy as it sounds muddled when I read it even if I know what I'm thinking.

I agree and understand your analogy, it was just the bit where you stated:-


I did notice it uses the word "parallel" in the description so maybe this applies to both senders. Either way at least one of them should be conservative now.

that made me post :) .


I think you're suggesting that the different values for Ch 29 and 30 is a sort of bias adjustment tuned to the different manufacturing variation of each car or variant?

I agree it must be to allow for differing shaping of fuel tank/capacity due to car/variant. Now we know a 2.0 TDi has the same ins.cluster as a 3.0 TDi but the 2.0 TDi doesn't have the same shape/capacity or number of senders so the bias of adjustment would differ plus could be to allow manufacturing variation of sender unit or allowing use of differing sender unit as I haven't checked but the 2.0 TDi may have different sender to a 3.0 TDi but :dunno:

[Splash]

I agree and understand your analogy, it was just the bit where you stated:-



that made me post :) .

No, hands up. I was thinking that parallel meant bilateral until I read about Ch 33 with a bit more thought (generating my dubious analogy). Previously my "tech censor" had intervened to prevent me studying the dark arts of VCDS and getting into deep water.

I'll see if just changing Ch 30 gives the desired result versus my notional 500 miles before I work out how to apply the right amount of bias (% or absolute) to generate a new value for Ch 29. Maybe I'm overcomplicating something simple.

And I thought O2 Gurus were clever... ;)

[gupsterg]

I think I have over complicated it :o and you have made me see the light!

The shape of the quattro car fuel tank is a kidney shape to allow for the drive shaft to rear wheel drive unit and this is also the reason for the 2 senders/pumps.

IIRC the left side of kidney is emptied first then the right side, for you to have your extra fuel only 1 sender unit need adjusting.

I will consult service manual and get back to you which is correct sensor/channel.

Everyday is a learning day! :D

I meddle/post to learn more as I think this is a medium for me to further my knowledge to help myself and perhaps others :) .

So thank you splash for your posts as well! :beerchug:

[Splash]

After the recent reset of Ch 30 to 96 and today's run of about 70 miles, I'm pleased to report that the tank is showing about half full since the last fill approx 250 miles ago. A tad over cautious, but a great result. It also explains why the previous setting of 160 was SO wrong, and I'm at a loss to understand how it even got there. Thanks for the advice Gup.