2006 Toyota Highlander Hybrid
 

In 2006 my wife and I traded our 2002 Highlander in for a [used] 2006 Highlander Hybrid. For a couple of years we consistently averaged 26.5-27.5 mpg on 92 octane fuel -- with and without the winter ethanol additive. So consistent was it that we just quit paying attention to it.

Early in 2011 I noticed that it was showing that the average was 22.3 mpg -- about the same as we were getting with the previous non-hybrid model.

We are retired and living in the Pacific Northwest where the weather is mild year round. Our driving habits and typical destinations/routes have not changed.

We tried resetting the car's computer and letting it re-learn everything but the avg mpg stayed the same.

We put new low resistance tires on and set the pressure to 37 psi. Rides like a hay wagon now but the mpg stayed the same.

Had the dealer check everything, looking for anything that might be contributing to lower mpg. They changed out the ECU for an un-related reason and said that they found no indication that the car wasn't running at design efficiency. The car still averages 21.7-22.3 mpg.

Has anyone seen something like this and do you know what was done to get back closer to the expected mpg for this car?

Thanks in advance for whatever help you can offer.

Hello Howard,

Welcome to this site. You might look in the Prius forum and post your question there, since your Highlander Hybrid's Hybrid Synergy Drive is similar to the Prius'.

Do you take your THH on long trips? Has your high voltage battery pack's state of charge dropped? I'm thinking perhaps your HVB is low, forcing your engine to run more. Some retired friends of mine took their THH from CA to UT, and got their best mpgs ever - 30 mpg.

Toyota put out TSB EG018-06 which allows '06 Highlanders with the 2AZ-FE engine to use ILSAC GF-4 0W-20W oil. That thinner oil might boost your mpgs 0.4 mpg.

Thanks. I'll re-post. In the meantime, you've raised an issue that could very well be related. I hooked up a TIS scanner the other day and it showed a low voltage fault. At the time I wasn't able to follow up on it but your comment makes me thing I should.

Is the charge level adjustable or is it a sign that my battery pack is just old and getting weaker?

The Prius can have its battery level read with a Scangauge II, but I don't see any xgauges for the Highlander Hybrid that would do it (unless the ones for the Prius happen to work with it).
It kind of sounds like the battery pack is worn out and its constantly trying to charge it. However, if it has been this way for over a year, I would think that the battery would have completely died by now, which would pretty much render the car unusable until replaced/refurbished (if its like the Prius).
Have you noticed any changes in the way it drives since you first got it? Have you noticed it not turning off at stops or rarely using EV mode? If it has a charge/assist display of some kind, does it display what you would expect, is it constantly charging?

Sounds like you may have a bad cell and your over all lost some capacity. I cant speak for the Prius system, but I know the Honda IMA system will go to almost 10% of its original capacity before it generates a fault code. In the mean time your mpg suffers and you find it charges more and assists less.

Usually that is from a bad cell and using a grid charger at 350 ma to float the cells helps it along.

When I first saw yout topic I was screaming Enginer PHEV as it can really boost your mpg because of how the Synergy drive system works and you coudl easily double or triple your mpg depending on the size you buy and how far you drive.

Thanks VSKID3 and Cobb. Sorry to be so slow in responding. Don't mean to be rude but granddads get pretty booked up when the weather gets nice here in the Northwest. :)

@VSKID3: No, our driving habits haven't changed and we don't/haven't noticed anything different other than the fuel mileage.

@Cobb: "...using a grid charger at 350 ma to float the cells helps it along..." What is a grid charger? Is there something I could look at that would explain it and show how to use it with the Highlander? Can I find out which cell is bad/weak and replace just that one(s)? Also, what is an "Enginer PHEV"? Sounds like something I should look into.

Btw, the dealer replaced the Intelligent Power Module in February of this year when we first took it in to see if they could determine why the fuel mileage had fallen off so much. But I don't think that was in response to the mpg but rather was related to a recall. At least it was notated as "Warranty Pays" on the bill.

It looks like the battery pack should still be under warranty (see below) but on two consecutive occasions the dealer has said that they didn't find anything that would contribute to the reduced fuel mileage. Surely they are checking the battery pack before making that statement.

Hybrid-Related Component Coverage
Hybrid-related components, including the HV battery, battery control module, hybrid control module and inverter with converter, are covered for 8 years/100,000 miles. The HV battery may have longer coverage under emissions warranty. Refer to applicable Owner’s Warranty Information booklet for details.