Generally High SOC, Battery Charging Uphill with "Green" SOC

What's your heater usage?

 

One possibility is that your original 12V battery has a shorted cell, which causes the engine to run more, trying to charge it, but it never gets to the value needed. Definitely you should start by checking it, as it is due to be replaced. If the engine is running excessively, then some of that ends up charging the HV battery. Make sure the engine stops running when you are at a stop. You should be getting better MPG.

 

Driving habits can use way more of the HV battery or way less of the HV battery... It's always better MPG wise to use the HV battery as little as possible. Of course when your charge is high its a good time to position the throttle so you use more HV power and when the battery is low it's a good time to position the throttle / brakes so you harvest more charging power.

 

I think the MPG is a function of the battery. If it is green, that is bad. Something is going on forcing it to charge, and the only way to charge is with the engine, so your MPG will drop. I think finding out why the battery is high will autocorrect the other problem.

 

Your driving habits.

How long have you owned the car and how many miles on it and what have you done to maintain the car.

 

^^^ What Ed said. How long have you had the Prius and what fuel consumption were you previously getting?

 

I am skeptical about the driving habits guess as a complete answer to this. In my car, it seems there is nothing I can do to get SOC to change much from 6 blues. Exceptions: going down hill (all green), and stop and go with A/C on (sometimes purples). If there are green bars going uphill, the battery arrow on the MFD will switch from charge to no arrow, and to discharge if I accelerate more. I think there is something else here.

Questions to J Skyler: When you accelerate quickly, does the battery arrow on the MFD switch to discharge? If you are seeing green bars SOC, it should do so without much effort. Can you do EV mode easily below 40 mph? You should be able to accelerate gently and not have the ICE turn on.

What's the mileage on the car? When did you notice the changes?

One thing I have noticed is that the car will adjust its behavior based on the slope of the hill. It has sensors to detect tilt angle, and it will use the engine more aggressively going up anything steep. I wonder if those sensors ever go bad. I haven't seen anything about it on PC, but if the car was thinking it was always going uphill, that would trigger the OP's symptoms.

 

Sounds to me as if you're over thinking things.
How fast are you driving on the freeway? How many miles is a typical trip?
Unless you're seeing big fluctuations in battery SOC I think your car sounds pretty normal.

 

Hardest but most important thing to learn to get good mileage in a Prius is not to engage regen. Its counter productive to mpg gain. Its braking the car. You must spend gas to get back up to speed. And It will hyper charge the battery too. Always in the green.

My wife drives the Prius mostly. She gets 43 av and the battery is always green. Always. She could care less about hyper miling and drives it like a regular car. Gas on gas off gas on. You get it.

When i drive it i can keep it out of the green and av 53 same route.

You must do all you can to not let off the gas pedal routinely. You must let off the pedal enough to slow down but not engage regen. Takes planning and looking ahead and proper speed for the traffic and careful pedal modulation and watching the consumption meter. It will quickly become second nature. Its worth 10 mpg's. You do not know how to do that yet.

That's step one to hyper miling. Its fun and easy.

Now if you think your car is sick here's the defacto test. Find a nice straight highway with little or no hills that's about 5-10 miles long. Get up to 55 mph. Engage cruise control. Rest mileage meter selection on the mfd energy screen. Says RESET. Zero it out.

A healthy prius in cc for 10 miles at 55 should reflect around 52 mpg's at the end of 10 miles. Unless its wicked cold. On a warm day should be at least 52.

 

That's almost exactly my experience too ed. I had an arm injury over Christmas and had to ride as a passenger with my wife driving. I could hardly believe how much of the time she had the engine running compared to what I typically get in the same route. This wasn't freeway though, so plenty of opportunities to glide, but none of those opportunities taken.

For me, green bars are like a green light for gliding and liberal use of full electric modes (and 5 or less is like a stop sign to use those modes sparingly). I often have to consciously try not to glide or EV too much so that I don't drop the SOC too low, whereas my wife in exactly the same car has it in green SOC most of the time.

 

Yep it could be part or all of the problem (though technically it's not really a problem, and the prius is generally more responsive to drive with a high SOC compared to a low one).

But there is an art to driving a Prius, if you really want to get the best out of it. (Though it's not really a problem if you don't know the "art", you just get fairly good fuel consumption instead of outstanding fuel consumption.) For example, if I drive my Mazda2 as carefully as possible, using every hypermiling trick that I can muster, the fuel economy only improves by about 8%. If I spend about half that much "hypermiling" effort on the Prius then the fuel economy improves by about 15%. I my experience there's definitely a much bigger payback for slightly modifying your driving habits (eg mild hypermiling) on the Prius compared to a normal car.

While driving style is a major contributor to this type of issue, there are however some actual "hardware" problems that will contribute to it. For example when I first got my Prius (s/h) it had a badly blocked rear battery ventilation fan. I didn't discover this for a while, but it was causing the battery to run hotter than it should and then the Prius was minimizing the battery usage to protect it (from further heating). This tended to have the effect of keeping the SOC higher and not letting it use that charge very effectively.

 

On my car, when my wife drives, we see about the same battery SOC as usual, even though she is, like the others above, not paying much attention to hypermiling. I have very low miles however, so perhaps what you are seeing is just a factor of, at 130K miles, an aging battery. The straight and level run test at 55mph is a very good idea.

Yes. I use PriiDash software on a netbook to see that. It is a great way to see more than you ever wanted to know.

Another important thing, and something often encountered here. Again, PriiDash allows you to see the voltage going to the battery fan, and the battery temps as well. The battery cooling fan should be almost silent, running at about 6-9 volts under normal conditions.

 

But the fan only comes on in overheat conditions not in normal temp day to day operation.

 

Actually I'd say that my (HV battery) fan runs most of the time in summer! Usually only at low speed though, you wouldn't hear it unless you place your ear right against the vent.

Back when it was clogged up it did run at high speed, which is what first alerted me to the problem. Since I've cleaned the muck out of the fan I've hardly ever heard the fan running at high speed again. It does however run very often at low speed.

BTW. I've got the unfortunate combination of fairly high temperatures and lots of hills around here. This is a pretty tough combination for the battery and it does cause it to get warm.

 

Yes we flatlanders don't have that problem. My car has never seen a hill before. Worst it see's is the airport parking garage. Plus I keep the interior cool with ac no open window hot cabin for me. I don't think my fan has ever turned on.