Intermittent "low coolant" warning

[OmegaV6]

Hi all .. car is a 2014 Allroad with the 3.0 litre TDi (245 bhp) engine. in the past week it's started giving intermittent "low coolant - stop engine" warnings that last about 5-6 minutes then dissapear, only to come on again at some almost random time, although part of me thinks they come on more often going uphill and go out faster going downhill !!!!!!! A part of me also thinks the warnings only start once the engine reaches full operating temperature - on the gauge that is.

Level has, obviously been checked numerous times ... its halfway between MIN and MAX when stone cold ( 2°C last night ) and a fraction above MAX when fully up to temperature but with the warning ON !!

I don't have any access to a code reader.

Any ideas what the problem may be and what, if anything, I can do to resolve it please ???

Ta muchly

[Crasher]

Try it on max from cold.

[aaronvg]

I have had this problem in the past on my A6 and also on my wife’s A4 it was due to a problem with the sensor in the coolant tank. I believe the sensor is in the bottom of the tank. I had the tank replaced on both cars and the problem went away and has not returned since. It was annoying as the loud beep when the warning flashes up always made me jump the tank is not expensive to replace.

[OmegaV6]

Try it on max from cold.


many thanks .. will do ...

[OmegaV6]

I have had this problem in the past on my A6 and also on my wife’s A4 it was due to a problem with the sensor in the coolant tank. I believe the sensor is in the bottom of the tank. I had the tank replaced on both cars and the problem went away and has not returned since. It was annoying as the loud beep when the warning flashes up always made me jump the tank is not expensive to replace.

Thanks, I'll try crasher's idea first !

[OmegaV6]

Unfortunately upping the level as Crashers suggests makes little difference, drive up a hill and the warning comes on .. level off or downhill and out it goes !! looks like a replacement header tank needed as I can't see the sensor being replaceable. Any one know a part number and/or reasonable source please.... and what is the recommended anti freeze for these beasts ?

Regards

O

[Crasher]

It will probaly be dirty sensor prongs, in my work it is more economical to replace the tank, which has been revised from 4G0 121 403 AC to 4G0 121 403 AG due to... false low level readings; seek and ye shall find! They are £33.50 genuine retail inc. VAT or you can get one from fleaBay for £43! Autod0c stock the Mahle CRT 60 000S but I am always nervous buying from them.

[OmegaV6]

Many thanks for that, local indie has quoted me £90.00 to replace with genuine .... £30.00 for the part, 1/2 hours labour, antifreeze. Seems reasonable enough to me as I'd need to buy both the part and some antifreeze, and now I've turned 70 I don't fancy working on the car in the weather forecast for next week ! (no garage available, all work is done outside!!) ... booked in for monday morning :)

[OmegaV6]

Car went in yesterday for the work .. couldn't be done as the part failed to be delivered !!

So done today .. part #4G0121403AG - £27.92 , labour £45.00 .. dreaded VAT £14.58 .. total £87.50 .. no mention of antifreeze on the invoice, but some has been spilt around the tank !

Will have to wait and see if it's fixed the problem as won't be going far for a few days - nowt to with covid .. wife has a knackered knee and can't walk, so playing nursemaid !! - and I won't use the audi for short journeys.

[OmegaV6]

Ah well .. drove it for the first time today.... warning came up twice in 60 miles .. out after less than a minute both times, and was on a level bit of road at the time. Level checked .. spot on the "max" mark when cold. Got to go out again tonight so wil see how it goes before taking it back to the garage ......doubt I'll get much support from them however ..... :(

[Crasher]

Hmmmm, odd. Where did the new bottle come from, was it from TPS?

[OmegaV6]

Hmmmm, odd. Where did the new bottle come from, was it from TPS?

No idea of their source, but the invoice quotes the audi number you referenced as the updated version ... perhaps I need to examine the item to check if it a genuine audi one ....

However .. a further "matter of interest" that serves to muddy the stgnant waters of my tiny brain ....

Tonight I did 2 x 35 mile journeys, with 2 hours between arriving at destination and departing. The car was well cold before we left as it had stood since 09.30 this morning.

On the way there I got 3 warnings in 10 miles . the first before the engine was even fully warm, about 1/2 way there on the gauge, each one went out within a minute, and all were "on the flat" as it were ..... I got no more warnings at all for the rest of the outbound trip.

Coming home the temp was down to about 1/3rd normal on startup and obviously got to normal temperature much faster. No warnings at all on the way home !!

So, could this problem be temperature related ?? no idea why that should be the case...

..... or has it taken a while for the "system" to recognise/recaibrate itself to the new bottle ?? Should a new bottle be "coded" to the car and if so, was it done or was it done wrongly ?

Or is it all coincidence and the intermittent problem still exists but just didn't happen so often??

Be interesting to see what happens on Saturday .. a return trip of just over 50 miles each way, again with about 2 hours between arriving and departing

Confused of North Wiltshire

[johnsimcox]

Ah well .. drove it for the first time today.... warning came up twice in 60 miles .. out after less than a minute both times, and was on a level bit of road at the time. Level checked .. spot on the "max" mark when cold. Got to go out again tonight so wil see how it goes before taking it back to the garage ......doubt I'll get much support from them however ..... :(
Surely when cold it should be on the Min mark, rising to the Max mark when the engine is hot. Is the issue that the system is overfilled?

[Crasher]

You don't get an overfilled warning, if it is way too much over max the cap will release the excess. The VAG protocol is to set the coolant at max when cold.

[OmegaV6]

More and more confusing ..... tonight the warning occurred 5 seconds after starting (obviously very cold) ..left engine running and checked level .... a fraction below "MAX" ...wiggled wires going into plug... warning was out by the time I got back into the car... so about a minute ??? Did 48 miles with a 15 minute stop in the middle .. no further warnings at all .....

If it was a broken wire/bad connection at the tank plug would that give a warning ?? ie is the warning triggered by powered on (float low makes circuit) or by power off (float low breaks circuit) ???

Really confused of North Wiltshire now ....

[OmegaV6]

Resurrecting this in the hope of some help .... Problem has slowly got worse, warning is now "on" more than it is "off" ... and the "off" is totally random ... might be 5 seconds or 5 minutes.. up hill or down, accelerating or braking .. who knows..... garage who did the work are saying its not the tank as that is new (and they refuse to consider a new one "might" be faulty) so it "must" be a wiring problem and won't give a price as "investigating wiring problems is an inexact time scale, might be a few minutes, might take hours"..... so basically want an open cheque !!

What I'd like to do is a little investigation of my own, for which I need a little bit of help... 4 questions really.. if anyone can answer them I would be extremely grateful..

1. How does the plug onto the expansion tank come off ?? (tried a straight pull and nothing happened)
2. Two wires into the plug, what should be voltage across them when unplugged with the engine running
3a. Two contacts in the tank socket, what should the resistance across them be when tank is full (light "should" be out), ....3b. resistance when tank is empty (light "should" be on)
4. Does anyone have a wiring diagram of the bits that include the tank sensor and other bits .. or do I need to subscribe to erWin to get one ??

With the above info I hope to use a meter to narrow down the possibilities... can't think of any other way to track down the fault ... unless someone knows better (highly likely!!)

Many thanks in advance