Something going on with battery or maybe transmission?

Tire pressure should be 42-40, your 12 volt battery needs to be replaced and your Inverter Coolant needs to be replaced and the throttle body needs to be thoroughly cleaned.

 

The dealer has to read some codes that have been set before they can offer any help. I have seen a number of these stories now, of vague loss of mpg. Ed has some ideas, let me offer a few others.

The symptom of engine racing is indicative of the hybrid system protecting itself, limiting the power through the inverter and the battery, due to excessive heat somewhere. It is not high enough heat that a DTC is stored, but performance falls off noticeably. The causes of this, can be, among many others:

1. 12V battery never comes to charge fully, due to shorted cell. This runs the converter part of the inverter assembly at max, and keeps the engine from shutting off. If you see 13.6V-13.8V after ~10 minutes or so, then the battery is OK. If it stays above 14V, then the car is still trying to charge the battery, wasting power.

2. As Ed says, coolant needs renewal. One can check for this with test strips.

3. If the inverter coolant pump is bad, but the weather is cold, you may not see errors, but cooling performance can drop off.

4. The HV battery fan needs to be cleaned. Many stories about this lately. The battery itself could get blown clean with air as well. Keep the thermal transfer high as possible.

5. Aging of the HV battery. There is a wide range of life spans reported for the HV battery here. Some stay good for a long time, some go before the warranty period. It depends on terrain and climate. Hills and heat are bad. Eventually a block will go bad enough to set a DTC.

6. Check the wheels for free spinning. Could be brake drag, although I think it is rare.

7. The transaxle fluid needs to be changed, if it has not been done yet. It can get overworked in hot hilly places. It is most definitely not a "lifetime" fluid.

A good way to sort this out is to use a Scangauge, mini VCI, or Prii-Dash software to look at the temperatures and see what is getting hot.

Where are you located? What sort of terrain?

 

Good suggestions from both Ed and nh7o.

Here's a couple of really easy self tests to perform.

1. With the engine warm enough to allow it to sit in ready mode without the engine starting, pop the hood and shine a bright flashlight from left to right (from your perspective looking into the engine bay) through the translucent inverter coolant reservoir (this is the "high" one near the inverter). Looking through from the other side of the reservoir you should clearly see some gurgling or turbulence near the top level of the pink fluid. If you don't see this then your inverter coolant pump is not working properly.

2. On a mild to warm day take a good 30+ minute drive, then stop and place the transmission in "P" mode. With it remaining in ready mode, get out and go around to the right rear seat and place your ear next to the fan vent. If it's not spinning at all then there may be a problem with the fan, and if it's running really fast then your battery may be running too hot (usually due to fur and dust obstructing the fan/ducts).

 

Was this before starting the car after letting it sit overnight (or at least several hours), or was it shortly after running?

 

Then it will probably drop to about 12.0 or 12.1 if you leave it overnight before testing. In any case the loaded value (11.7) is the most telling. Your battery is fairly weak but it's probably not bad enough to cause your specific problems. ("probably not" meaning it possibly could be the issue, but not highly likely in my opinion). I'd still consider getting a new 12V battery soon.

BTW. What was the load that you used when you measured 11.7? Did you use the headlights, or just the "Ig-On" loading?

 

The cheapest and most telling way for a home owner to check the 12 volt battery is to buy a battery charger at Sears for $49. that has 2 amp mode and a swing meter not an LED. Hook the charger to the front under hood jump points and note how long it takes in 2 amp mode for the battery to charge to 0 current draw.
For comparison my new Optima will charge to 0 current draw in about 6 minutes.

Many of us routinely put our batteries on a charger at least once a month and bring it to max charge. Noting how long that took. The car can never achieve max charge as there will always be a load on it. Max charge once a month is very good for battery health.

 

I just had my hybrid battery replaced and I am now getting better mileage than before. I was getting about 45 mpg when taking a certain route. I am now getting 50 mpg on the same route.

It looks like the new hybrid battery has helped the mpg.

 

A clogged air filter will reduce maximum engine power but probably has little impact on mpg. Regardless, why not just go out to your car, open the hood, and remove the air filter.

Hold it up to the sunlight. If you cannot see light coming through the filter, replace it now.

 

Hope not. That usually means there's one in the cabin filter too.

 

Don't bother having the dealer check your 12. For some odd reason they always report its OK.
Just change it out and move on to the next maintenance the car needs.
If your dealing with the dealer alot ask him how much they charge to replace the trans fluid.
The service writer will say its a lifetime fluid which is a joke, just say that's great how much?

 

I had the same problem with my 2007 prios with 45,000 miles on it. It turned out to be a stiking brake caliper on the rear. after it was replaced the milage whent from 36 mpg to 44 mpg in winter weather.

 

that's a big expense for 5 mpg's?

 

I have had an inexplicable loss of MPG over the last 1.5 years, and while switching out the winter wheels by myself for the first time, I noticed the rear wheels weren't turning freely. I regularly use the foot/parking brake and so I suspect that did something to the calipers and/or other rear brake components. I am taking it to the dealer Monday morning.

There were about 3 days this past winter where the MPGs started going back up and the vehicle seemed to travel faster with little power input. I suspect the rear brakes may have suddenly loosened before sticking again.

Now I do have an SG II, and would appreciate any input on what parameters to look for in addition to coolant temperature (FWiA ?). Thanks.