Engine Idle concern: won't shut off, runs high

I've noticed the last few days that my Prius seems to be dropping MPGs horridly (even worse than the typical winter drop). The engine will idle hard and loud when stopped sometimes or when braking even. I noticed this morning, when I am braking to a stop, the MPGs are registering at 75 or below and it's running when idling and it seems to be running the gas engine more. It will sometimes shut off at a stop light, but hardly at all the last few days regardless of if it's been running 5 minutes or over an hour.

I thought maybe it was because it's cold-- we've dipped to single digits, but have been above 30 or so the last week or two and has only happened in the past two or three days. It happens at start up and at the end of my hour long commute to work. I've turned off the defrost and heat and it still does this.

She's a 2005 and has just over 105,000 miles. I just had her oil changed, a fuel injection cleaning and spark plugs replaced two days ago and had the inverter serviced and recommended transmission work done at 100,000 miles. Her water pump was replaced in the last year with the recall. I just replaced the air filter. There are no warning lights, so I"m not sure if anything would show up with the codes. I'm worried because it did not do this previously, and started to as soon as I got the car back from the injector cleanings and plug work...

Has anyone else had this happen? Or does anyone have any ideas? I skimmed through the forums and saw a comment for a 2001 about a traction battery possibly needing replaced and the end result being a replaced computer...

I plan on calling the dealership once they open today...

:welcome: to PRIUSchat. :cheer2:

Most likely the problems stem from a failing 12V battery. Their typical
service is ~4 years, although some folks have gotten 6 years of service.

http://priuschat.com/forums/newbie-forum/73400-weird-stuff-happening-mpgs-dropping-test-battery.html

Overfilled oil also results in MPG loss.

As Rokeby has said, the 12 volt battery can cause all sorts of weird problems when it fails - and it often fails about 4 or 5 years old. Unlike in a traditional car the Prius 12v doesn't have to crank a starter motor to start the engine and as such is not easy to tell when it is starting to fail.

I guess you have two options, the first being to pay about $200 and replace the 12 volt and see if that helps and the second, more expensive option is to go get the car diagnostically tested at a Toyota dealers.

If your 12 volt battery hasn't been replaced already, then you're going to have to replace it whatever you decide.

Thanks guys!

I'm hoping that's all that is... relatively cheap compared to other things that can go wrong with a vehicle. I'll be swinging by there after work to see if that's the issue and will touch base back when I know. A co worker wondered if something may have been knocked loose during mantainace, but noted the 12v may be the culprit as well. I'll be checking the oil before I head out to see if that could be part of it.

I've had the car a little over two years and doubt the previous owner replaced it so I may bite the bullet and get it over with regardless today and see if that resolves it.

It could just be the engine running to create heat. Give it a quick test with all heat and A/C off and see if it still does it.


Re the 12v battery. Do the service menu test as described here to measure the battery voltage: http://priuschat.com/forums/gen-ii-...conditioning-12v-aux-battery.html#post1188923

For the OP: When you say you "had the inverter serviced", just exactly what does that mean? Normally there isn't anything to service on the inverter. It either works, or you replace it.

Tom

Inverter was checked over at the 100,000 mile mark. It wasn't replaced, but they had changed out the fluid for that if I remember correctly, and I had the transmission done in the last year or so. They generalized it to "inverter serviced" and "transmission serviced". Sorry for that confusion. Beyond a serpentine belt replacement, nothing has been replaced since I've had it extending beyond any recalls (water pump). This was done at the dealership so I'm assuming the properly bled the system to avoid air pockets re: inverter. I have a trusted mechanic, but anything relating ot the engine I take to the dealership to be cautious.

I have tried turning off the a/c and any heat. I had initially thought that to be the case when I left work yesterday. The engine makes a similar sound to when I am going up hill as far as the pitch and type... I don't have a scanguage or anything to pull exact numbers unfortunately. When it idles hard it's well beyond anything I've had just running the heat, particularly since I've been keeping it low or off to see if that was an issue. I had a car transmission slip and spike RPMs with little movement signifying the end of it's transmission, so I"m a little weary...

Haven't had any throttle body work or cleaning, but will add it to my list of "possibilities" to work through.

I've been at work so I've been unable to run the maintenance mode, but will hopefully get a few minutes soon, or a chance before I leave to see where it's at so I have some additional info for the techs.

Thanks for additional input!

How much state of charge are you seeing on the HV battery when this happens Ninja?

Just ran the maintenance mode:

AC: 12.1
with a current load (but not on): 11.8
Ready mode is 14.3

I'm thinking the 12v battery may be the ticket judging by the ranges given in the instruction thread... the cars been sitting for 6-7 hours with out running. Either way I have something to bring to the techs since it will have to run an hour before I get to the dealership!

Thanks so far guys! This has helped immensely!

? ? ?

Whoops, I didn't read that part.

Still it's harder to completely turn off the heat than many people think. I've found that even if you have A/C (and auto A/C) off, if just the fan is on then the heat is still on. You have to turn the fan off too, or set the temperature down to "max cold".

Percentage wise, I'm not sure, but the battery icon is no lower than a bar or two down as of now or of late... it's in the green or top end of the blue, lowest. Glancing at it on my way in today the graphics show the gas engine running a lot. But when in idle whether it's idling higher or not it doesn't show any power going anywhere on the diagram from what I noticed. It's feeding ot the battery and wheels when driving. If this didn't answer your question, let me know and I can try to hit more specific points! I haven't noticed anything specific when it idles, but then again I haven't looked specifically at it while in drive to see regarding the HV.

If the engine is running but arrows are not going into the fully charged battery then I would say the car is either warming up or warming up the heater or both. Are you having a colder than normal winter or just noticed what the car is upto more?

It's actually been much more mild. It does it whether the heater is one or not and regardless of how long the car is running. An hour of high way driving and the engine is still kicking on when braking leading to MPGs reading 75 or below when it should be charging and the mileage is suffering horribly. It feels like it's not driving as well...

So, before heading to the dealership, at 8 hours with the car off I had the following volt readings:

11.9 no load
11.3 load
14.2 on
which was lower than the reading only a short while before...

I drove a little over an hour... hour and a half to the dealership and the readings I took when I got there were:

12.3
12.1
14.3

It seems like it isn't holding charge, which may explain why it seems so much worse int he mornings after sitting for 12 hours? I had the numbers and explained everything to the intake people at the dealers and provided these readings. I should hopefully know shortly for sure...

I kept an eye on the battery icon and it seems to stay a consistent two bars down, with little increase or decrease relating to a question earlier...

Definitely appreciate the input! I don't think I would have thought of the 12v battery... I'm hoping this is it but will touch base once I get word for sure. It's very helpful to get input

Hmmm odd. My car exhibited similar issues about a year ago for a couple days, though not as bad as yours, before it brought up a hybrid warning one morning. The HV battery would stay one bar from full and the engine would rev and then sometimes it would run ok and then others it would stay 3 bars from full.

Turned out to be a failed/failing HV battery ecu which was replaced under warranty. This was found easily under warranty but I guess could be expensive if not. At least your 12v looks like it's failing anyhow and will need replacing one way or another. If the problem is still there replacement then good luck.

It seems to have been the 12v battery. (whew!)

The tech had tested the batteries and run diagnostics and said nothing came back indicating an immediate issue. Initially both he and the service person had suggested to drive it around a few more weeks to see if it got any better. Resistant to the idea, I ended up talking to the tech about the symptoms directly. He reviewed the read out, but showed that one for the 12v had printed "Good-recharging" which was in support of the idea that it is working, but not holding a charge well... there was just nothing to lead the battery to "condemnable". The HV battery was fine and he said the system is doing what it's supposed to, just that something was causing it to read that it had to run. He had thought maybe an oxygen sensor, but noted there were no codes which was not pointing to a specific problem. Any time I've taken the car for maintenance it's been after work with over an hour drive, which is why it wasn't a red flag when I had it in on Tuesday as it was closer to normal readings.

After a few minutes, there was a general agreement that it's obvious it's not holding charge well, and that since it's 6 years old, it'd need done sooner than later and may resolve the issue. So I bit the bullet and replaced it.

Both my drive home and my drive to work were much smoother and the car seems to be back to how it used to run (mpg's and all!).

Thank you again for all of the input! I don't think they would have found a solution without the information and direction I had received! Being a girl, I particularly value having some grounding to make sure I'm not played and that things get taken care of. The battery was still a bit pricy in itself, but small in comparison to other things.

Turning off auto and the fan is the most important part.

I almost NEVER use auto. For me, to get the ICE to turn on/off at will to provide cabin heat when FWT (Fahrenheit Water Temp) is low (<146 F), heat at max and fan on/off is good enough.