You may have run though a bad tank of gas, and not shaken the ill effects yet. Pulling the battery will reset some of the fuel trim tables (or whatever they are called - don't pile on me for nomenclature). As they re-build, you may see it decrease again, in which case it's time to do more research. Otherwise, happy motoring.
Other things that could affect the fuel mileage detrimentally over time:
-dirty air filter.
-alignment and/or tire wear (that's likely a stretch, though).
-ambient air temperatures (decrease will reduce fuel economy).
-changes to driving style (Captain Obvious at your service).
-mechanical issues like spark plugs, sensor problems, etc (that would also likely throw codes).
-less boost from the hybrid battery.
SOME SAY, that when he gets into his car, he plugs the IMA cable into his left ear … but no one can tell who is charging whom!
Last edited by CR-Z Canadian; 05-09-2017 at 07:54 AM.
Reason: fix glaring typo