2010 X5 35D Diesel Exhaust Urea Reservo

Funf, you've helped me before and you're active on the DEF related forums so maybe you have an idea regarding this speculative question.
Imagine that for some reason(s) a diesel owner has ignored the warnings and the mileage count down, finds himself in the middle of nowhere with the urea tank empty and the warning stating that his X5 will not start once he shuts it down. Could you fill the tank with water and would the vehicle start, or is there some advanced sensor that can determine that it is not merely the level of fluid but tests for ammonia content? In an emergency could this procedure work and would there be any damage to the system?
Might not even be an emergency, maybe the local dealer says they won't top off the tank to get to the next oil fill and the owner just doesn't want to pay for the solution and so he wants to get by for the next 1K miles or so.

Originally Posted by zimmerrk

Could you fill the tank with water and would the vehicle start, or is there some advanced sensor that can determine that it is not merely the level of fluid but tests for ammonia content?

No.

DEF is available widely, such as at many parts stores (AutoZone, Advance Auto, NAPA, etc.) VW dealers, Ford dealers, Dodge dealers, and almost all truck stops. It typically cost less than $10 a gallon.

"Sensors in DEF tanks will notify the driver if volume is low or
if the product concentration is not of good quality. Another sensor will
indicate if the NOx level in the tailpipe exhaust is too high."

The EPA would not approve an SCR system which would allow the use of plain water.

Originally Posted by zimmerrk

....Could you fill the tank with water and would the vehicle start, or is there some advanced sensor that can determine that it is not merely the level of fluid but tests for ammonia content? In an emergency could this procedure work and would there be any damage to the system?....

What Penguin posted

Funf Dreisig

My 2011 warning light came on at 20,000 miles. Went to a dealership out of town. Oil was low. The dealership said BMW engineers thought the service could take place during scheduled maintenance. At 22,000 miles the warning light came back on. Scheduled service call next week. Anyone else with this problem?

Originally Posted by Zingo06

My 2011 warning light came on at 20,000 miles. Went to a dealership out of town. Oil was low. The dealership said BMW engineers thought the service could take place during scheduled maintenance. At 22,000 miles the warning light came back on. Scheduled service call next week. Anyone else with this problem?

Do you mean DEF instead of oil? Did the dealer add DEF when the light came on at 20K mi? Did they completely fill or just put a bit in there?

Yes, sorry I meant diesel exhaust fluid. The warning is DEF remaining in the reservoir. At 20,000 miles the dealership filled the reservoir.

If they did completely fill it and it is low again in 2K mi, then I think they need to find a leak or replace the metering unit.