Adblue

[Izzug]

Just got a warning "additive failure" accompanied with the ad blue yellow warning and a message saying "700 mls remaining " sounds like the add blue pump has failed....not happy

[evdama]

Just got a warning "additive failure" accompanied with the ad blue yellow warning and a message saying "700 mls remaining " sounds like the add blue pump has failed....not happy

Possibly crystallised.
Our works vans got through countless tanks until the drivers were told to just keep enough for the week in.
Problem went away

[Izzug]

Warning says 600 mls now, car booked in for next week, only done 20k, I'm assuming that the system does not have any direct feedback at the the system operating, how would it know? So what generates the fault signal?

[boop]

There are sensors in the AdBlue tank.

[notsofast]

Possibly crystallised.
Our works vans got through countless tanks until the drivers were told to just keep enough for the week in.
Problem went away

Interesting. A worker in the parts department in my local dealership advised the opposite - he said or implied it was more likely to crystallise if the level is really low, I think his reasoning being it could become more concentrated due to evaporation. I don't know if this was company information or just his own speculation, though the manual recommends topping up "as soon as the first alert is issued indicating that the reserve level has been reached", so maybe he was paraphrasing that and drawing his own conclusions. Though I've tended to let it get low so that there's not so much old stuff hanging around inside the tank when new liquid is added - what I've read before has suggested it's the age of the adblue that affects how readily it crystallises (and the experience of your work vans possibly confirms this). Do you know how many miles per week they were driving?

[Izzug]

What sort of sensors in the tank? Just a low level sensor would give you the addblue warning, I get that , but how does it 'know' it is not adding fluid?

[evdama]

Possibly crystallised.
Our works vans got through countless tanks until the drivers were told to just keep enough for the week in.
Problem went away

Interesting. A worker in the parts department in my local dealership advised the opposite - he said or implied it was more likely to crystallise if the level is really low, I think his reasoning being it could become more concentrated due to evaporation. I don't know if this was company information or just his own speculation, though the manual recommends topping up "as soon as the first alert is issued indicating that the reserve level has been reached", so maybe he was paraphrasing that and drawing his own conclusions. Though I've tended to let it get low so that there's not so much old stuff hanging around inside the tank when new liquid is added - what I've read before has suggested it's the age of the adblue that affects how readily it crystallises (and the experience of your work vans possibly confirms this). Do you know how many miles per week they were driving?

Average 600 per week.
The tanks were nearly 20litres and never got less than 80percent full.

Running it low goes against the grain for us old timers having had it preached ad-nauseam that you top up fluid levels as a religion.

The units were just swapped out for new ones by the fleet operators maintenance monkeys so we never really got to the bottom of it ,if you excuse the pun.
I would have tried a hot water flush to see if it would clear the warning.

[Izzug]

AdBlue light and warning now extinguished. The recall software has been updated, maybe it has just reset some counters and the AdBlue warning will be back if I don't use too much, don't know how it 'knows ' , doubt there are flow sensors in the tank, but boop says that the tank does have sensors, can't just be the number of times the low level sensor is triggered as evdama says the constant full tank does not give problems. So crystallised fluid seems a good bet. Perhaps short journeys, engine still cold, dont know if AdBlue operates when cold? Maybe my next fill will just be distilled water! Does anyone know more details about how the AdBlue works?

[kingy1912]

AdBlue light and warning now extinguished.  The recall software has been updated,  maybe it has just reset some counters and the AdBlue warning will be back if I don't use too much, don't know how it 'knows ' , doubt there are flow sensors in the tank, but boop says that the tank does have sensors, can't just be the number of times the low level sensor is triggered as evdama says the constant full tank does not give problems.  So crystallised fluid seems a good bet. Perhaps short journeys,  engine still cold, dont know if AdBlue operates when cold? Maybe my next fill will just be distilled water! Does anyone know more details about how the AdBlue works?

The injector knows when it is injecting and at what pressure. I assume if the tank stops pumping to the injector or the injector is receiving no fluid it give a light for a blockage. As for crystallisation i have no idea how it knows that specifically. However i did read about the use of optical level sensors so it is possible it has one in the tank (part of reason why they are maybe so expensive) that gives different messages depending upon the light that returns to it.