prius state of charge goes way down

Sounds like you might be having the start of the HV battery going bad. People discribe that the state of charge of the HV battery varies wildy in a short period of time as one of the symptoms of the HV battery going bad. I'd take it to the dealer and let them check it out. Keep us updated.

 

No, you're not causing any harm, just drive it gently until it's warmed up.

Edit: Where are Patrick Wong and the other experts when we need them?

 

Just curious: How many miles are on your Prius? Have you been the sole owner?

 

What is the weather like where you live? Is the car really cold?

 

I have noticed a similar reading for the past two summers.
It happens just as the OP described - usually when there is a heavy initial
draw on the battery (e.g., reversing uphill out of a parking space). Also
typically when there has been no warm-up, and for me anyway in relatively
hi ambient temperatures. the SOC display can go from half-wayish to one purple
bar instantly. The good news is that after a few minutes of driving the battery
display goes back up to half-way. The engine runs as though it display is
the true SOC (no stealthing allowed), but the rapid recovery time always seemed to
me to suggest that the true SOC was not being read correctly by the sensors during
those first few moments of start-up and go.

At all other times the car behaves just fine and I'm still going strong a year and a half after first seeing the "symptom". No failures, so no trips to the dealer. I put it down to being a "quirk" rather than a harbinger of impending doom.

 

Could it be a MFD fault? Does the radio go off too?

 

Hi PG,

One person in Colorado who had a steep initial uphill, and did not realise what the car was doing did eventually have to get his battery replaced.

I think it would be prudent to start the car, and just let it do the 1 minute dance stationary, then proceed.

Did you typo when you said SOC down to ZERO ? That seems wrong. Did perchance you leave out a leading digit like 4? Or 40.

 

I had noticed very similar behavior as the OP on my 2006. At times, I would pull out of the garage in the morning with the display at 5 or 6 bars and by the time I drove the 3 blocks to subdivision entrance it would be down to 3 bars or occasionally 2 bars in the purple (flat, paved roads, no A/C or heat running, always in vent mode). Other days, it would only drop 1 or 2 bars.

I also found the car was much more prone to charge the battery up to the green zone (7 bars). Up until the car was 2 years old, I would very occasionally see the green (maybe 1-2 time/week) on my very repeatable suburban commute and usually after I had to brake quite a bit. After about 2 years I would see it charge into the green 1-2 times/day, a lot of the time driving at a steady state on flat level roads. On one occasion I was driving on a 45 mph, flat as a pancake, surface street I had traveled on hundreds of times. By the time I had driven about 5 miles (no stops) the car had charged all the way up to 8 bars

The charging behavior the last year I owned the car was considerably different car compared to the first two years. The funny thing is, the wild charge swings were the only indication something might be amiss. My mileage stayed the same, the car always ran great and there were no MIL warnings.

 

Since you have an uphill drive upon startup, I agree with your decision to let the engine warm up for 45 seconds prior to driving. Considering the relatively stable SOC readings once the car has warmed up and the excellent mpg that you achieve, it doesn't sound like your traction battery (or the drivetrain for that matter) has a problem.

By the way, do you note that the MFD SOC bar gauge corresponds to the SOC readings on your Scan Gauge?

I do not think it is necessary to have your car checked out unless you see the red triangle and the MFD warning - either hybrid vehicle or traction battery icons.

 

I'm having a somewhat similar problem with my 2006 Prius. I've had it since August 2006 (sole owner), and it's got almost 40K miles on it.

About a week ago, the battery vent fan came on high for the first time ever. This happened right after I started it; it was about 11 pm, outside temp in the low 80s, and the car had been turned off and locked for about two hours. I stopped the car after going about two blocks to try to figure out what the noise was, and I left the car idling as I went through the owner's manual. (I found the section on the battery vent and verified that the vent was not obstructed.) By the time I was done (maybe 5-10 minutes), the state of charge had dropped to the purple range. I turned the car off and then re-started it. The battery fan didn't come on, and the state of charge started in the purple range but was in the high blues (probably 1-2 bars short of green) by the time I got home (about 3 miles away).

Since then, the battery fan hasn't come back on, but the state of charge has been varying far more than normal. Two or three times, the state of charge has been almost to green when I started the car, dropped through the blues as I backed out of the driveway and started to drive on the street, and dropped down to purple within about two blocks. It may be worth noting that the drive to the main road from my house is uphill--a gentle slope, not a steep grade. When I start driving at higher speeds on the main road (30-40 MPH vs. low 20s from my house to the main road), the state of charge steadily goes back up to high blues within a few minutes.

This sudden variation in the state of charge has never happened before, so I am concerned. I have not gotten any warning lights, and the car runs fine--no shuddering, no weird noises.

I'm planning to take the car in to the Toyota dealer later this week for an oil change (it's due) and to ask them to run a diagnostic on the hybrid battery. I'm hopeful (probably naively so) that because the hybrid system is still under the 100K warranty, they won't charge me to run the diagnostic.

Does this sound like a bad hybrid battery, even though the car only has 40K miles on it? If so, how likely is the dealer to try to blame the battery failure on something I did and refuse to honor the warranty? The only service that hasn't been done by a Toyota dealer is replacement of all four tires about 3 weeks ago (done at Costco) and some bodywork completed about 8 months ago. Has anyone heard of dealers blaming other shops for damaging the battery even when the work had nothing to do with the battery?

 

I don't think that your traction battery is bad yet, although it may well have lost capacity compared to when it was new. If you ask for a test of the battery without any warning lights on, you will probably be charged for diagnostic time.

When you first start the Prius after it has been resting overnight, the gasoline engine will not produce power for a brief period until the catalytic converter has warmed up. Ignition timing is retarded during this period of time. So, if you have to climb a slight hill at the start of your trip, the energy needed to do this comes from your traction battery. This is why you see the battery SOC go down, then come back up after the gasoline engine has warmed up the catalytic converter and is producing power to spin MG1 and charge the traction battery.

I've also noticed that the SOC gauge on my 2004 shows greater variation than in the past (currently have 86K miles on the odometer). I attribute this to the battery aging and reduced capacity, but it is not bad enough yet to make warning icons in the MFD appear.

 

Patrick, thank you for your quick and thoughtful answer. I hope the battery isn't losing capacity already, but that may be the case.

I just scheduled an oil change at the Toyota dealer for tomorrow morning, and I described the SOC behavior to the service manager and said I was concerned. He said he would ask the techs about it and that any necessary diagnostics would be covered by the warranty. Of course, he could sing a different tune when I show up in the morning.

I'll update the thread after the service call.

 

I am having a similar problem with my 2007 Prius.

The SOC seems to fluctuate quite rapidly and frequently now. I can be at blue stop at a light for 10 seconds and it will drop down to purple. My MPG's have gone down to almost 40 (I have never driven the car correctly, but I average around 46).

Of more concern to me is that I can park the car with a green/blue charge for 1hr, come back and when I start again, it will be on purple.

I have taken it to the dealer and they said that the battery checks out fine. All cels working properly, but I just don't believe them.

Any suggestions?

 

I took my car to the dealer today for an oil change and a battery diagnostic. The diagnostic was covered under the hybrid system warranty, thank goodness, but it came back clean--no error codes.

I'll continue to monitor the state of charge and to document how frequently and under what conditions the charge drops so quickly. I really want to isolate whether it only happens on that uphill drive when the engine is cold or whether it starts happening under other conditions.