DEF info

DEF specificationISO 22241-1
Capacityabout 4 gallons
Shelf lifeIt expires, don't hoard!

How to read the remaining DEF in the tank

Using VCDS or similar:
01 Engine ->
  Advanced Measuring Values ->
  IDE 05232: Reducing Agent Fill Level

result is a % of filled

Other things you can query:

IDE05232Reducing Agent Fill Level% full
IDE03142Remaining Vehicle Distance Until
Reducing Agent Deficiency
IDE03144Used Reducing Agent Since Last Servicegrams
IDE10032Reducing Agent Quality Sensor: Urea concentration% ureaShould be 32.5%
IDE10246Reducing Agent Tank Volume Actual Filteredml≈ 13,400 ml
IDE10247Reducing Agent Tank Volume Actual Calculatedliters≈ 13.4 L
IDE03143Remaining Engine Starts Until
Reducing Agent Deficiency - Bits 0-7