Unexpected hybrid behavior

Hi all. I have a 2008 with 188K and the original traction battery. Aside from my brake controller failing last year (chirping when stopped, and eventual loss of pressure) which I wrote about replacing, we haven't had much drama since getting out Prius in Feb of '14 with 130K.

The past two months our economy has dropped noticeably. We've had many ongoing weeks of 95-100 degree days. The A/C compressor is always at the highest speed I see (viewed with mini VCI), the blower at the highest speed, and the radiator/condenser fans have also been at their high speed. I chalked up the economy, high 20's to low 30's to the heat, short trips, and a traction battery that I suspect is weak. One indicator that is different than I expect is that unless I am going down a long hill, the battery is almost always at 2 or 3 bars of charge. I know that it's normal, especially in summer with the AC on to get to low states of charge, especially while driving in town. Even on the freeway, the acceleration to get to highway speed with the A/C running takes the battery level low and it really struggles to recover back to the normal range - it may not be above purple for 10 or even 20 miles. Available acceleration, as expected, is usually pretty low.

Yesterday I started noticing a different behavior. I am very familiar with the warm up processes and the different phases associated with it. My wife and I were out yesterday where I had 5 miles of slow-speed in town driving with several stops, 10 miles of highway, and 5 miles of congested city driving in the early evening. The temp was 95 and I had the idle-check when stopped before I hit the freeway. When I got off the freeway to a light that I knew would be red, I slowed gradually as I normally do, to recapture what I could. The hybrid charge indicator was two bars above the middle - where I normally expect it to be. However, once stopped, the engine started with quite a noticeable jerk, like it does when the AC is running and the battery is too low. I turned off the climate for a moment (long light), and it didn't change the behavior. There were actually a couple more jolts, often like what is felt when it does it's idle check. The battery was still showing an indicated better than half charge. I put the AC back on and continued driving through the city. Each time I would stop, the engine would be in a stopped state, but would start up again just after I got stopped. This happened 10+ times at lights I got stopped at. The battery never dipped below 4 bars of charge, and I also had acceleration assistance like I would expect with that state of charge. In some ways this engine starting behavior mirrored what I would expect if I were at a low state of charge. One difference though, is that usually if I turn off the AC in these situations and it isn't as starved for power, the engine usually remains off for short stops (I try to run with the AC off in the evenings and with the windows down in town, but my wife was with me and is intolerant of hot temps and windows). I did make sure that I hadn't accidentally moved the drive mode to braking.

After we left dinner to go to a movie (after dark and 80), things seemed back to normal. We drove about 10 miles to the theater. The A/C initially ran high to get things cool, but rapidly achieved the desired temp and wasn't working hard. About halfway there, again knowing that it was fully warm, it started the same behavior. Starting right after I was completely stopped. It did this every single time we stopped until we got home. The electrical load would have been minimal, and traction battery was showing a normal state of charge.

There were no fault indicators present during any of this. I haven't yet pulled out mini VCI to look at things, but I will be doing that later today.

Honestly, if I didn't have a battery state of charge showing a normal level during this, and if the engine had stopped at least some of the time when the AC was off, I would have just assumed that the battery was at a very low state and it was trying to recover. I suspect that my battery is extremely weak, and unusually, very even, and possibly just below thresholds as far as internal resistance goes. I don't know why it would show a relative high charge and act like it was at a critical level.

I've not been sure whether or not I would replace the pack if/when it failed. I like this car, but I don't love it. It's great in town, but for me, miserable on the highway due to the amount of tire, wind, and especially engine noise that are constant companions. I had grown used to it, but got a taste of a new, quiet, comfortable, powerful vehicle when my wife was hit in a parking lot and we were without the Prius for a week.

My question really is, what are your thoughts about the behavior I experienced last night?

 

Well rats, I forgot about this big issue. When the previous owner traded in her car at the Toyota dealership, they replaced the battery, and a month later it must have been bought at auction from the small car lot I bought it from. I'll read how to properly test the battery, but I'm pretty sure it's gone. Using Techstream, I read the voltage of 14.01 volts in ready mode. With the ignition "on" but not ready and everything else turned off, it immediately read only 11.8 - far too low.

RANT ON I know I am preaching to the choir, but why does this have to be such an issue. My dad's 2001 Cadillac DHS is the only other car I've worked on with a battery in the passenger compartment (under the rear seat). That battery is easily 2 times the physical size, and 3 times the weight. His first replacement occurred 11 years and 3 months after he bought it. If that battery can last such a long time (and it's not unusual in that generation) with far more simplistic electrical - at least as far as battery charging goes), why can't our batteries regularly last more than 3 years? RANT OFF

I did pull 3 active codes (no check engine light or ABS/Traction lights on) - one for ABS ECU malfunction which would explain the 3 times we've started the car and there has been no power assist. One for a rear wheel speed sensor (wheel that was hit in the accident), so I'll be taking it back to have them check it out, and one for transmission power supply.

So the first course of action for me is obviously to replace the auxiliary battery after truly confirming the voltage, but I'd be 95% sure it is bad. I'll see how it effects the other issues. I'll look at the battery threads, but what is the current best aux battery and from where? Last time I was on here there were complaints that the Optima was even worse than the stock battery.

As far as bumps or engine misbehaving, that wasn't an issue last night. The roads we traveled on were almost all new, but thanks for the info.

I'll update this after checking

 

You are right JimN. It looks like the Optima reviews are pretty good after all. The price is surprisingly much less than when I looked casually a couple years ago. Those who experience issues are of course those who speak the loudest.

I didn't end up purchasing the Optima. I found an ACDelco branded traditional AGM. Don't care about the brand so as much. This is a brand new item on Amazon, and I bought what showed as the last in stock. The battery has a 24 month free replacement and a "lifetime" warranty. Not sure how well it will be supported, if at all, but it did have one positive review showing proper a proper fit in a Prius. The price was about $20 less than Optima, however, there was a 20% off coupon there bringing the price to $101 shipped. that made it worth taking a chance on.

 

Augustus88, the engine shouldn't have been hot, it was in a slightly cooler part of the day, and it has been through much hotter days recently with no issue. When I got the codes via Techstream all temps were good.

Last night I had the behavior happen again, while in a long drive thru. I had long enough waits to observe the behavior, and it really behaves the way I expect it to when the traction battery is down to 1 or 2 bars. She. I'd sit long enough, it did eventually turn off, however the moment is let off the brake it started, and then stopped when I applied the brakes and remained off for 10 or 15 seconds and then started right back up. One new behavior is that sometime during this wait, the consumption miles reset, but the average economy didn't just like when you fill the car and drive off without manually resetting it.

Bad news about the battery order. It came today, but I was shipped an ACDelco 78AGM. Unfortunately, the original vendor I bought it from wasn't expected to get stock until after the 23rd of this month. Too long for me to wait, so I ordered the Optima. The only good news is that because batteries require special handling, I get to keep it. It's too bad I just put a battery not even two months ago into my TrailBlazer I received the appropriate battery for it (and really, quite expensive given it's AGM). I'll make a little back from selling it though.

 

The traction battery, yes. I'm not sure what normal temps are, but it's usually tops out around 105-108. With those temps, it sets the fan speed to 2 (out of 5).

 

I finally received the correct battery last week. I'm happy to report, as expected, that all is back to normal. I find it amazing what issues this can cause. I would love to put an ammeter inline with this battery to see what is going in and out. I've read a lot of posts about it needing 20-30 minutes to charge, but that doesn't make sense to me. Even at a constant voltage charge, the draw to turn on all the low voltage systems and run them until the contactor engages shouldn't be that much total energy.

Thank you for the contributions and reminding me about this potential failure point. I'm glad that was all it was, though I must admit I am thinking about getting a grid charger/discharger to recover some of the performance from my traction battery. It's very well balanced according to techstream, but just doesn't have much capacity. My wife, whose primarily drives this, absolutely loves it. She just isn't sure of putting that kind of money into it not knowing for sure how much effect it will have. She's perfectly happy with it as it is. I, however grow tired of the sound of the engine running so hard, which is seems to do often in these temperatures. I've always hated 4-cylinder gasoline engines, especially at high RPM. I like the mileage and relatively low operational cost (mine seems a bit higher than average), but I struggle to love the car.