msaudiq5

Have s6 for a year and recently noticed mpg dropped from low 20ish to 14s.
First thought it's colder temperature but in couple days I noticed cylinder deactivation seems never get activated anymore. Also, when i tried to use Auto engine on/off I received a message: 'System failure. function is not available'.

Taking car tomorrow to the dealership but was wondering what is in common between those two symptoms?

I know in my BMW there is a second battery for on/off engine operation - does Audi use the same technology?

tenspeed

It could be a thermostat stuck open. If the engine is cold, it runs richer and it might not allow the Auto engine on/off to function.

How is the temperature gauge and heat into the cabin?

Part of the low MPG's could be underinflated tires. Should be read cold but you can have them checked during service.

msaudiq5

you may be on something about thermostat! It started when I started to heat the car when temperature dropped to 40s. Tires are fine - i do check them. I'll update the forum tomorrow after the dealer visit.

MikeS6

I actually have a question about the Cylinder Deactivation. I honestly have not ever really noticed it come on/off. There's no light that comes on right?

msaudiq5

there is no direct indicator light for cylinder deactivation function. I see it on consumption (current mpg) display when bar is climbing to the right and become green with green battery sign on the right.
Now I see it will never coming green and mpg <16.

VitaNick

Carbon buildup

msaudiq5

3 days later got my car back. the problem was little temperature sensor.

arrivalanche

Good to know!