Decreasing Gas Mileage in 2002 Prius

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.

 

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.

 

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?
.

 

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

 

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.

 

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!

 

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

 

Which Exide model did you use as a replacement? Is it around the same size as the original or did you have to secure it differently?

 

As long as you have the Panasonic Battery that came with the Prius, no modifications are required. It bolted right in with my car. The terminals are perfect, and the battery is warranted by Exide for 8 years. You can throw away the stupid vapour tube that Toyota has on the original battery as the Exide spiral cells emit no gasses. If you live in Canada, here is the equivalent. Canadian Tire sells the exact same one for $30 cheaper! The first pictures includes most features found on the extreme, except the one that fits in our car puts out 54 amp hours, while the Panasonic puts out a mere 37 amp hours. In -20 degree centigrade weather during winter time in Canada, the car still registered over 12.8V before startup. The Panasonic from Toyota in similar weather would register about 10.8-11.2 volts. Its a hugely impressive battery. Plus my mpg improved, and I don't have to replace the battery ever 2 years as with the stupid Panasonic one. Plus my Toyota dealership said they are going to look into advising customers about this battery as they tested it themselves and found that its far superior to the Panasonic in all conditions. Plus I have a 300W amplifier in my car, and it can go for over half and hour and the engine does not fire up to charge it. No problems at all. And I think I used the word "plus" enough times to kill a horse! HAHAHA!!! I guess I got carried away with my discovery!

 

No shims? Which model?

I went with the Odyssey PC925 and still had to make some adapter jumpers. So far, works great. However, I want to replace my wife's 2010 battery with something with more capacity.

Bob Wilson

 

Hmm, the Exide batteries look to be about 7" wide on the smallest dimension, compared to 5" for the OEM battery. The hold-down clamp doesn't look like it could take anything wider than 6" at best. The other two dimensions look like they can take the extra sizing...

 

Ahh, OK, I read the older posts, so to answer my own questions, the Panasonic battery was the replacement for the OEM in the TSB, and I need the 04003-23147 aux battery installation kit which is larger and will fit the larger Exide battery.

 

I too was experiencing gradually decreasing gas mileage over the past year or two. Then, the check engine and warning light came on and the fault codes P3000 and P3009 were diagnosed indicating a battery leak. I decided to replace the battery after my dealer agreed to a 50/50 split of the cost. Since I received my car back 5 days ago, I have noticed a signficant improvement in gas mileage, some 7-8 mpg greater, despite the fact that the A/C has been on continuously over this past week. I am hypothesizing/guessing that as the individual cells begin to fail within the battery, some loss of power occurs with the resulting need for the gas engine to fire more frequently, thus the decrease in mileage. Since the car was still driveable, even with the warning light on, I was wondering if each and every cell within the battery eventually failed, would one be able to drive the car solely on gasoline?

 

Dear friends. I'm new on forum, from yesterday I have 2001 Toyota Prius with huge millage, over 170k. I don't understand what I see on consuption screen. My MPG is very high for Prius, it shows 19 mpg when I started engine in cold Chicago weather (around 40 degrease), after drived few miles when blue light with termometer turn off (what this light mean?) mpg changed to 27, is it my consumption for a right moment and my average will be better or it is what my car really burn and I only make max 27 mpg. If yes, why is so high? What should I check in my car to get an answer? I don't understand what my LCD screen show with battery regenrated, after I drive some yellow squares show up with letter E, it's growing, but never go higher than 1/3 high.
I don't have my owners manual, maybe someone can show me where I can find some instructions what screen shows. I really want to understand my car and I need your help with this, I want to thanks in advance for everybody who helps me.

 

Welcome to the club.

The NHW11 (2001-03) Prius is inefficient when cold. As a general rule, we try to use:

• lower bumper air inlet block - I use a split water noodle but anything capable of blocking the inlet helps retain engine heat.
• 1-2 miles at 25 mph - try to run the car through slow-speed streets for the first 5 minutes at speeds of 25 mph and using "N" when feasible. When stopped at a light, shift to "N" to reduce fuel consumption until the car can go into Stage 4, full hybrid mode. At that point, the engine will automatically stop. Search the messages for "stages."
• 0-38, 45-65 mph - try to use these speed ranges. The lower range keeps the car in hybrid mode so the engine can cycle on-off as needed for high mileage. From 45-65, the vehicle is also pretty efficient. There is a hybrid control law transition at 42 mph and I try to avoid that speed or speeds close to it.

Check my mileage.

Try to drive so you don't have to apply the brakes and your mileage will improve. This often means driving at the speed limit and learning to find 'pacing' vehicles like large trucks to follow. Being somewhere first means coming in last in fuel efficiency. Patience and you'll do fine.

Check Ebay for manuals, they come up from time to time. Also, consider having your transaxle oil changed. This can reduce your cold-weather rolling resistance. Also run the tires at the maximum sidewall pressure. Finally, check the engine oil level and make sure it is below "F" and above "E." Overfilled oil has a bad effect.

GOOD LUCK!
Bob Wilson

 

Thanks for the excellent suggestion. I was at 32 mpg with a 2002 Prius with 80,000K and after replacing the transaxle fluid and 12V battery, I am now back to 42-46 mpg. :cheer2:The local Toyota wanted $400 just to replace the 12v battery but took in the notes from the PriusChat Forum to my trusty repairman and he charged me $350 total for everything. The only issue was he had a hard time getting the computer to recalibrate. For a few hours after the work, the car kept dying but they just kept driving it and the computer re-set itself. :rockon: Love to all of you crazy PriusChat forum people. Peace, Debora

 

Try rebooting, resetting, what ever it's called. A simple procedure.