I have a 2006 HCH II that i purchased new and have serviced only at the dealer. Up until around 45k miles it returned around 42-46mpg in mixed driving. Mileage dropped to consistently under 40 around the time that i changed the original Dunlop to Michelin X Costco tires - i thought it might be the tires so it was hard for me to localize what the problem was.

At the last service i asked for a software update to 'get up to date' if there were any changes that might improve my mileage. Afterward what i noticed was that the IMA indicator seems to be more inconsistent and i won't get any assist from the IMA particularly on an uphill grade at around 4 bars showing. I had experienced a similar lack of assist previously but only when the indicator was down to 2 bars or less which was very rare and happened only in the summer or if i had used the AC a lot. Now this was happening several times during a brief drive.

After discussing with the dealer they decided that the battery was beginning to fail and agreed to replace it. While fuel economy seems to have been improved by a few mpg the indicator is still all over the map and the lack of assist at around 4 bars is still there. During a 2 hour all freeway ride there will be times on a slight uphill grade that the engine begins to race and the indicator is down around 4 bars and no amount of pressing on the accelerator will provide any assist.

So since it doesnt seem to be a battery issue does anyone else have any clues as to why this is happening and what i should ask the dealer to look into next?

Thank You.

 

I have a 07 that had the update done, and mine does the same thing. Learn to drive the hybrid all over again.... I try and stay out of EV only mode, and I can keep above the 4 bar freezeout. I also will use the "S" if I get to the 4 bar, it takes no time to get your soc back up.

Now that I have learn to re-drive the HCHII my avg. is back to 45.9 with 90% around town driving.

The HCHII is not a car for a person who does not take an active role in the MPGs it is not a normal car. It is meant to be driven frugally. Knowing what I know now about
the car I would still buy it again. If I wanted a Corvette I would have purchased one, you do not drive one of those for the mpgs, but the hps...

 

The upgrade that they put on (I'm guessing TSB-058) is designed to manage the battery pack better. It decreases the assist affinity when you are below 5 bars of battery, but it increases the affinity at 5 bars and above. That upgrade is designed to run in combination with the transmission software upgrade (from what I've read online) so make sure they have done both--if not there have been some reports of weird behavior (which you could search for here). However, I would say your car is functioning similar to others here who have been upgraded.

That's interesting that you dealer replaced the battery without any serious CELs or anything.

 

I am far from driving it like a Corvette. As i mentioned i got reasonable mileage driving it for the first 45k miles of its life. The problem seems to have happened over time (decrease in mileage) and then suddenly different behavior with the software update. I found a thread over on Edmunds and it seems like there are quite a few complaints of similar problems with the IMA brought about by software upgrades so i will talk to the dealer some more about it particularly the TSB for the transmission update as well.

 

They had to talk to the district/regional manager about it since there were no error codes but it didnt take too much arm pulling. I think they are feeling the heat from the IMA problems and poor performance/reviews from the HCH as well as Insight and don't want to get too much bad press and falling even further behind the Prius.