Decreasing Gas Mileage in 2002 Prius

[Blue Moon Pearl]

I've always gotten in the mid-40's until the past year. MPG decreased slowly over past year, but didn't cause concern until recently when the loss sped up. During past month, it's dropped from 41 to 40.2. Also, the turtle light has come on twice for the first time ever. Car is not due for oil change/ check-up for another 1K miles. I've not been doing anything differently in my driving or fuel choices that I'm aware of. Have any owners of older Priuses experienced a similar loss? Is this to be expected over time? Thanks!

[fthorn]

My 2001 just started doing this, too. Got new tires and I went from 50 to 46. Now this weekend I am like 42.

I'm ready to give up on it.

[JimN]

I'm not an Electrical Engineer but it sounds like the 7-8 year old traction battery isn't holding a charge as well as it used to causing the ICE to run more. New tires will also cause a bit of a hit but that will be temporary as they wear in.

[john1701a]

Originally Posted by Blue Moon Pearl

Is this to be expected over time?

Yes. As the years & miles pile up, efficiency will drop.

Of course, that's true with non-hybrid vehicles too. In their case, things like cylinder compression decrease causes more fuel to be consumed to deliver the same amount of power as in the past.

How many miles?
.

[bwilson4web]

Originally Posted by Blue Moon Pearl

I've always gotten in the mid-40's until the past year. MPG decreased slowly over past year, but didn't cause concern until recently when the loss sped up. During past month, it's dropped from 41 to 40.2. Also, the turtle light has come on twice for the first time ever. Car is not due for oil change/ check-up for another 1K miles. I've not been doing anything differently in my driving or fuel choices that I'm aware of. Have any owners of older Priuses experienced a similar loss? Is this to be expected over time? Thanks!

The NHW11 Prius traction batteries appear to impact mileage as they reach the end-of-life. The lower Ahr capacity requires the engine to run more often. Eventually, one cell will fail and you will start getting worse errors. Also, the battery fan will run more often and longer.

Proper diagnosis is to measure the battery module pairs, which your Toyota service center can do with a scanner. Ask them to read out each and give you a listing of the 19 module pairs. If the highest and lowest modules differ by more than 1.2 V, you have a failed cell and the time has come for a hard decision.

You have been changing the transaxle oil?

Bob Wilson

[Blue Moon Pearl]

Originally Posted by john1701a

Yes. As the years & miles pile up, efficiency will drop.

Of course, that's true with non-hybrid vehicles too. In their case, things like cylinder compression decrease causes more fuel to be consumed to deliver the same amount of power as in the past.

How many miles?
.

143 K miles. Thanks!

[Blue Moon Pearl]

Originally Posted by bwilson4web

The NHW11 Prius traction batteries appear to impact mileage as they reach the end-of-life. The lower Ahr capacity requires the engine to run more often. Eventually, one cell will fail and you will start getting worse errors. Also, the battery fan will run more often and longer.

Proper diagnosis is to measure the battery module pairs, which your Toyota service center can do with a scanner. Ask them to read out each and give you a listing of the 19 module pairs. If the highest and lowest modules differ by more than 1.2 V, you have a failed cell and the time has come for a hard decision.

You have been changing the transaxle oil?

Bob Wilson

Thanks! I'll take your info to service center and will ask about the transaxle oil.

[mlibanio]

Try changing the transaxle fluid, replace it every 60,000 miles, trust me it helps! Also replace the stupid Panasonic 12V battery with an Exide Spiral Cell Battery as I did, I got at least 2-3 mpg back. I thought it was the traction battery causing my mpg drop, it was that stupid Panasonic battery that I had to replace every 2 years. The spiral cell battery is amazing in temperatures as low as -24 degrees centegrade up here in Canada. Car was registering at least 12.3 volts in that weather. The Panasonic even when new would show 10.6-11V in similar weather.

[abundantlyyours]

Originally Posted by Blue Moon Pearl

I've always gotten in the mid-40's until the past year. MPG decreased slowly over past year, but didn't cause concern until recently when the loss sped up. During past month, it's dropped from 41 to 40.2. Also, the turtle light has come on twice for the first time ever. Car is not due for oil change/ check-up for another 1K miles. I've not been doing anything differently in my driving or fuel choices that I'm aware of. Have any owners of older Priuses experienced a similar loss? Is this to be expected over time? Thanks!

YES! I've recently experienced a loss of power, as well as decreased MPG. About 10 days ago, when driving home on the highway, I started losing power while on cruise control, and even when I turned it off. Since then, it's daily, off and on. I hit the gas, and the gas is going *some*where, but the car doesn't respond. My car has over 160K miles on it, and I usually average around 36.8. When checking after the last 1200 miles, it's now down to 32.9!

I've always gotten regular oil changes and service, and took it in for this specifically last Monday. They did replace the air filter and repair/replace something about the spark plugs, and said they could then follow a misfiring to cylinder 3 (or some such tech talk), but couldn't find anything after that. They said they noticed something wrong with oil burning/usage and they're now having me do periodic visits to have the oil level checked (after 500 miles today, then after 1000 again). I'm supposed to be waiting to find out if I might possibly have to rebuild/replace the engine. Help!

[tochatihu]

abund, there seem to be several things going on in your case. A messed up engine is possible, surely, but not at all what we expect for Prius.

One very useful diagnostic not discussed yet is engine oil analysis. If there is metal wear enough to burn oil, you will get very unusual results.

It costs 20 or 25 dollars and could greatly simplify your diagnostic landscape