Sudden Mileage Decrease

[JanetP]

I have a 2013 ES 300h. I bought it January 2013 and already have more than 72,500 miles on it. Yes, I know, I drive a lot, which is why I bought this particular car. I wanted comfort and good gas mileage. Up until Feb of this year I was consistently getting between 36-38 mpg. In stop and go traffic on the LA freeways I would get 41-43. Suddenly the mileage started going down and now it's at 32-34 mpg. After a fill-up, I'll get the 36 mpg until I hit about 7/8 to 3/4 of a tank. Then it drops. I also seem to get better mpg on highway; it used to be the other way around. The battery never seems to charge all the way. I have done the following to try and improve the mileage:

1. Increased tire pressure
2. Oil changes
3. New tires
4. Fuel injector cleaning
5. Replaced air filter
6. Checked the spark plugs
7. Used Chevron instead of Costco gas
8. Took it to the dealer to have the battery checked out

Has anyone else had the same or similar problem? Any suggestions about what caused the mileage to degrade?

I found something online about the rear brakes causing drag and degrading the mileage on a Prius. That's my next step but I thought I also post here.

Any suggestion is welcome.

[lenore]

Maybe it needs a ISC reset, not sure if it applies to your Hybrid, but on the RX400h it helps.

[JanetP]

What's an ISC reset?

[lenore]

Here is ISC reset....Please note you do not need the scan tool, just make sure the engine is warmed up.....

isc reset..pdf

[engnrng79]

What does the dealer say? All hybrid components are under warranty in California until 150,000 miles. Any codes? Does the displayed mileage match your calculated mileage at each fill up?