Indicator fluid...my mate asked his Mazda dealer about the "Adblue" light on his CX7 dashboard.
Dealer says yeah, bring it in...it needs to be topped up.....it will cost $300
He bought 20 litres from somewhere for a few bucks and did it himself....I think it used 15 litres.
Maybe we could start a thread on automotive maintenance rip offs. I was told years ago by a Kmart workshop that my front brake pads needed replacing....I took the car in for a wheel balance. I told them to leave the brakes alone....and those pads were still on when I sold the car 3 years later.