2010 prius, 31 mpg, Toyota doesn't care

Have you checked your 12V battery? No one has mentioned this yet, but with the low MPG and now a malfunction light on the dash, it might be due to get checked.

Have you accidentally left the dome light on or some other action that may have drained the 12V battery?

Even if you haven't, it's possible it may be bad also. Unfortunately, this does happen from time to time, even with new ones. The brake warning light shouldn't have any affect on the MPG from my understanding.

I wouldn't recommend either dealer you've gone to thus far based upon the information they've given you. Hopefully you'll have another dealer option!

 

Your dealer doesn't seem to have a good understanding of the GenIII (no bladder, etc., as mentioned by prior posters). Doesn't necessarily mean that they're evil or don't care, but they do seem uneducated on the redesign.

AFA the FE, you definitely *will* observe a mileage drop as the weather gets colder; this is true in any car. However, in your case, as you describe it, it sounds like a sudden change, not a gradual drop as one season blends--er, in New England, I guess the better word would be 'plummets'--into another.

Even here in MD, now, I notice a significant drop in MPG on short trips. On a longer, highway trip, the mileage bounces right back up. I recommend trying Donee's test, but don't be too disappointed if you don't get the advertised 60+ at temps over 32F. There are a lot of variables involved in the whole thing, but as you describe it, something does seem amiss. Good luck and keep us all posted. And be a squeaky wheel with your dealer--it's often the only way.
~T

 

the one time u/a that you experienced and nobody is talking about may be the source of your problem, but there is no advice to be had because it cannot be duplicated and produces no codes. my advice would be to trade it in on an 11 as soon as they are available.

 

A bladder law?!? Now they're just makin things up!

I have read that a bad 12 volt battery can cause poor mileage and various other bizarre symptoms, so as wick1ert said, that might be worth checking!

 

You definitely need a new dealer. The brake warning light should have thrown a code. While the light itself might clear after X successful starts, the DTC should still stay logged in the ECU as a "history" code. It's definitely time to find a new dealer.

Unfortunately, Vermont is a bit of a hike from DE. I've got a copy of TechStream (the toyota diag software) and a cable. I'd be more than willing to run a "health check" through it on your car if you were local or swinging through the area. I'm not an expert on TS by any means, but can navigate and do a few things with it.

What was the voltage on the 12V? Make sure you run a no-load (car off), IG-ON (press power twice without pressing brake pedal), and under load (turn the headlights on in IG-ON).

 

Hey they might be on to something there. Are you in a hilly area? Perhaps the altitude sensor is malfunctioning and your are running rich.

 

A failing 12V battery is one of the "usual suspects" for falling MPGs.
This could occur with a new vehicle due the dealer failing to fully
charge the 12V battery during routine pre-delivery preps.

A second suspect would be a dirty MAF sensor.
This wouldn't be typical on a newish car.

The following is speculative. The unique, non-repeated sudden
acceleration incident may hold the key. Perhaps an insect or other
piece of airborne debris got past the intake air filter. To do so, the
filter would have to be ripped or improperly seated.
Unfortunately, this has been know to occur at a dealer servicing.

FWIW, here's a thread that discusses the very important difference
between cleaning the throttle body and the MAF sensor:

http://priuschat.com/forums/gen-ii-...roubleshooting/57617-cleaning-maf-sensor.html

[Edit] It also typical for service techs to reset tire pressures to ~35 PSI.
If you run at 42/40, this can drop as much as 5 MPGs.

 

I agree that you should keep after them. In Boston, my FE dropped by about 4MPG when temps plummeted, but your situation seems to be much worse, so you need to keep after them to find out what's wrong, so that you can get back to enjoying your Prius. We love ours!

 

From the sound of it, I think that "running rich" means something a bit different to his dealer, and it has absolutely nothing to do with combustion.

 

The 12 volt battery powers the computers, but has nothing to do with starting the engine in a Prius, that is the 201 v battery.

 

I hate to say it, but with the brake "warning", could the OP be driving with parking brake on? It's possible the driver is pressing the parking brake pedal accidentally instead of regular brake. That would explain the "lurching episode", if brake was released.

 

Hi noexcuse,

How hilly is that route, and did you use cruise-control?

For flat terrain, cruise control would be more consistent for a test. For hilly terrain I think the reverse would be true.

The next thing to do is go through the mileage questionaire, and write down actual measurements in response to the questions. Comments like " it was ok " are worthless in any evaluation. You need to provide numbers. So far, I only see numbers in regards to mielage, and no numbers in regards to anything else.

What was the wind like on that drive? Saying " I tried this " implies the conditions I gave were followed, but you did not give us any numbers.

The cruise-control comment is an attempt to take out variation in the test. The Prius accelerator pedal has a range around which the car maintains constant speed. One can press further in in that range, and get about 20 mpg worse mileage, than lifting to the point at which speed is just maintained.

Of course, I have no knowledge of you, or your personality. And somebody with nervous, frustrated attitude might push on the accelerator pedal at the point where the car is just short of speeding up, rather than just slowing down.

Try the test on level terrain (like Ohio) and use the cruise control. Please document all aspects of the specific circumstances. We really cannot help without this information.

This line of comment was brought out by your comments regarding the battery voltage . You need to be measuring that with a 1 % accurate DMM, and it needs to be above 12.0 volts after a day long rest. Do not assume tire pressure is right because the car is new, or the oil is accurately filled.

The first engineering job I had a boss that had a comment about any engineer who used the word assume, or implied he was assuming. You need to get into that attitude to be able to figure this out.

 

Why not just test the car yourself?

Random driving gives real-world results, but not a basis of comparison. What you need to do is go for an efficiency cruise, intentionally trying to exceed that 31 by a wide margin.

Go for a drive on flat 55 MPH highway. After at least 10 minutes, the engine should be toasty warm. Press reset. You should see MPG in the mid-40's. Exit off, press reset, and drive at 30 MPH. That MPG should exceed 50.

Doing that, I see those numbers routinely... despite the cold.
.

 

Maybe you can find a hybrid owner's group or a lone hypermiler in your area to take your car for a drive? Somebody with a ScanGauge or other tool to hook up to your car - somebody that has the appropriate experience and tools to tell whether the engine is idling too much, or not using regeneration as much as it should, or even if everything appears to be fairly normal. Then you can go in to the dealer and say "the engine doesn't shut off at a stop", and that gives them something more concrete to work with and test against.

 

Well, my gas mileage has taken a big hit in the winter. I'm driving it in the snow (winter wonderland) and it's only a mile (but to far to walk in the dark.... I know a baby...).

The cold weather and short trips have really dropped my mileage. I would contact regional office and discuss with them. good luck...

P.S. Not sure if you tried taking a friend with you to talk to the dealer... If you came on to hard (yelling and screaming) they may be blowing you off. It's not right that they did that but you want your car fixed, so take some extra steps...

 

My experience with dealers (not just Toyota) that they will ignore owner complaints about mileage as everyone knows that the biggest variable is a driver and the same car can have a huge range of MPG depending who drives it and how.

Unless you produce objective evidence of problem (engine malfunction light condition or dripping gas from fuel line), there will be no action on the dealer part. I guess if you ask them politely to check for problems most likely they will do some rudimentary check for basic issues.

Example: my prius is capable of doing 70+ MPG in best case scenario driving when route is long enough and temps mild enough. Yet it only does under 25 MPG in 1 mile only driving when cold.

If my commute was only 1 mile, 25 MPG would normal too.