Just got a Jazz MPG seems too low?

[guest3821]

Yes that is correct, the Jazz in common with most post 1996 vehicles will have a 'learning' type ECU. Apart from the manufacturer's base settings the ECU is monitoring other parameters such as fuel quality and knock values and then optimizing fuelling and timing accordingly in an effort to achieve optimal performance including fuel consumption.

That's certainly true, but it's not a long term thing - the ECU is doing it all the time and will react to a new tank of fuel or if you drive at altitude. 

I'm not aware of any that "learn" the driver's driving style.  Imagine a car used by a couple who had very differnet driving styles (which is likely to be quite common) - the car wouldn't know where the heck it was!

You are correct of course regarding adapting to driving styles and I should have worded my reply more carefully.
 
The ECU however is constantly monitoring, and thus 'adapting' longer term, to more than just fuel quality. Cold start and idle speed control are just two examples of processes affected by 'learned' ECU data.

[degzi]

with ecu's "learning"
They take reading from engine sensors and adjust air/fuel mix then check on emissions side of things, then adjust as necessary. Simples

See if any faults are stored, do a service, see if things improve, if not, get a multimeter and check lambda sensors  reading on cat. Most of the time bad mpg is caused by an old crusty sensor somewhere. And odds on its a O2 sensor in my experience.

Google testing lambda sensor if you don't already do it.