45 mpg to 29mpg 2007 prius

Is the engine running any more than normal?

 

Chances are you are running the heater since it is colder than normal this year. This will keep the engine going a lot more as to add heat for your needs. You may want to consider a grill block if you need the heat in the cabin.

 

wukas3 – My guess is the drop in fuel economy you are reporting may well be from a confluence of events.

>> Cold Autumn-Winter’ish Illinois weather.
>> You may be using your heater on your 60 + 60 = 120-miles daily commute.
>> Switching to burning “Winter Blend” gasoline.
>> Replacement of the 12-volt Accessory Battery resetting the HSD.
>> The new Costco Tires you purchased may not be LRR.
>> At 211,000+ miles, your Traction Battery may be getting “long in the tooth,” and is beginning to have trouble efficiently taking and holding a charge, especially in the colder weather, requiring the HSD to cause ICE to run more to keep it at spec’ed charge levels.

Reaching your goal of 300,000-miles on your 2007 GEN II/2G may require you to replace the aging Traction Battery between now, and reaching your 300,000-miles goal --- Replacement of the Traction Battery, with its associated couple thousand dollars expense, may be required sooner rather than later --- maybe even during this 2014-2015 Winter Season.

FWIW – Toyota’s annual Fall/Winter/Holiday Season Toyotathon is under way; maybe a 2014 Model Year Closeout priced or new 2015 Prius would look good under your Christmas Tree this year.

 

In addition to what's already been mentioned......what about necessary routine maintenance, like plugs and air filter ?
With high mileage vehicles the CAT converter is also a suspect.

 

As a red light was on, read the code at a good auto parts dealer, drop like that might be a spark plug not firing, actually, I suspect a non firing cylinder.

 

if a plug wasn't firing, you'd know it. the car shakes and bucks like crazy. I had a plug go bad and I thought the engine was gonna blow. cel was flashing-- scared the heck out of me.
make sure your tires are inflated to 40 psi, check that air filter, and also I've read about the seatbelt blocking the vent for the battery fan causing poor mileage. is the fan working? could it be full of dust or dog hair? my '06 had a mouse nest next to the traction battery when I got it, that could have just as easily been in the duct. you will have to partially dis-assemble the rear cargo area to check the fan but its worth it.

 

Try cleaning the air throat and sensor, there is a special spray for that. Personally I think just a clean cloth suffices.

 

since the mileage has not been the same since you replaced the 12 volt, perhaps it is defective. seems to be happening a bit, lately. what kind did you put in?

 

You are within driving range of one of the best independent Gen2 repair facilities in the US. It is in southern Illinois. Give Steve a call: Prius hybrids sales and service Scottsburg Indiana . He can be trusted.

My opinion is that you bought the wrong tires and are running them at too low a pressure (Cosco does NOT know about Prius maintenance).

JeffD

 

I have just started to have the same problem, I'm in the uk and I'm not using the heater any more than normal, I service my car inbetween annual services and I have gone from 59mpg down to 50 in a matter of weeks, I use it as a taxi but I always have done so no change there

 

Oh a ve also noticed that when I coast to a stop the engine is still running when normally its shut off, is it a sign that the high voltage batteries are on their way out?

 

You haven't said what car you are driving, but presume seeing as you've posted here it is a Gen II Prius.

Have you had your car more than a year? In the UK when the winter formulation petrol is switched in, there is a sudden and noticeable drop in fuel economy. 9-10 MPG is about right. People, such as yourself, who refuel frequently are more likely to notice this than others. I would only worry if your economy continues to drop.

Not necessarily, it could be that you are in Stage 3a/3b and not transitioned to Stage 4. Remain stopped until the ICE cuts out, then the car should behave as you remember. If it is not this report back.

 

Thanks for the reply, yes it is a genII, it's also due its routine service so I'll do that, is there a way to check the hv batteries?

 

What year and how many miles has it done? You should update your profile with your car model and year, so people don't have to ask.

You could purchase a Mini VCI cable with Techstream and you can check it out yourself, or use a dealer for your service and you will get the Hybrid Health Check (HHC) included. Provided the HV battery passes the check, the warranty on the HV battery is extended for 12 months. This can be done every year until the 10th anniversary of the car's in service date. If you do not use a dealer for servicing you can still take your car to the dealer for a HHC, but you will have to pay £39 for the check.

To date no one has reported here that their car has failed the HHC, that I've seen.