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Hybrid system warning light....and how I fixed it

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Michael48, Dec 13, 2016.

  1. Michael48

    Michael48 Junior Member

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    Recently, my bluetooth signal went away and I was preparing to replace the radio unit. Then before I could do that, while sitting parked, my hybrid system warning light message came on with warning lights for every other system. The car would start fine but along with the warnings, my cruise control would not work either. I have some tech experience and scanning produced no codes. After thinking about it, I took a volt meter to my 12V battery and checked the voltage. While the car was running, it was over 14v. Without running it read 12.3 but with a drain from the headlights and heater, it quickly dropped down to 11.4. All in less than five minutes. I replaced the battery with new and all errors and non functioning systems were once again working correctly. The car runs great and no more issues. I hope this helps someone with their issue.
     
  2. bisco

    bisco cookie crumbler

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    welcome! great post, thanks! had you run the battery down at all in the past? 4-5 years is pretty young.
     
  3. zoeboi954

    zoeboi954 Junior Member

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    It's not your 12v battery. all you did was just reset the system when you unplugged the 12v battery. your check hybrid system will come back on. self experience.
     
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  4. Eclipse1701d

    Eclipse1701d Prius Enthusiast

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    A weak 12 volt will cause all sorts of issues. Erroneous codes are one of them. There is no guarantee, but from previous posts I have read, over the years, you may have no further problems. Good luck!
     
  5. Rebound

    Rebound Senior Member

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    Not necessarily.
     
  6. ChapmanF

    ChapmanF Senior Member

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    If I may ask, what scan tool did you do the scanning with? I'm asking because there are many scan tools out there (and most of the generic ones) that are only able to see the industry-standard OBD-II codes, and few or none of the ones specific to Prius. And, it turns out, most of the codes that light the Prius master warning light are the Prius-specific codes that generic scan tools don't see. That leads to a lot of threads on PriusChat where the first post says "hmm, getting the master warning light and there aren't any codes", which is rarely, if ever, true: the codes make the MWL light up.

    Those voltages are no worse than what I'm used to, in a car functioning entirely normally, so I hope your problem is solved, but I won't be astonished if it comes back, as zoeboi954 suspects. If it does, and you weren't using Techstream to scan for codes before, I would recommend doing that (or going to someone with Techstream to have it done), and there probably will be codes, and that will be the start of tracking down what the real trouble(s) may be.

    I know there's a strong belief on PriusChat that 'low 12 volt battery' can be the explanation for any code or set of codes not tracked down to any other cause (even when that's just because no one has tried yet). For whatever reason, my own experience has been different. I've had two different Prii for a total of 8½ years now, and codes I've pulled up have always been traceable to real causes, related to what the manual says they mean.

    My day job's in IT, and I'm totally familiar with the possibility of out-of-spec voltage causing computer glitches. I've repeatedly, though (not on purpose) had seriously drained batteries, in my Gen 1 several times down to 8 or 7 volts during the start request. I'll vouch that the car is hard to start that way, but once started, it hasn't begun making up random codes. (I have managed to glitch the computers by bouncing the cable clamp when reconnecting the battery, and had to disconnect and try again to get a clean boot. Usually the codes in that case will be a slew of Uxxxx codes from every other computer in the car, saying they can't talk to the one that glitched.)

    I can't explain why everybody else sees random codes at hardly-even-marginal voltages, and I don't even down to 7 or 8 ... somehow, all the Prii that do that are getting sold to people who aren't me.

    In case you do get the light again, and can pull codes using Techstream, it would be great if you could update this thread with the codes. There are just so many different issues that can light the master warning light, there's no real way for someone else to judge whether your fix would be their fix, unless they can see whether your codes are their codes. (And even then, most codes point to a few usual-suspect causes that still have to be pinned down, not directly to a single cause.)

    -Chap
     
  7. zoeboi954

    zoeboi954 Junior Member

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    If he getting 14 volt charging, 12.3 resting 11.4 under a load from the fan and lights for almost 5 min. That battery Is still good. Prius will start perfectly at 11.4 volts. and remember it's a small battery. I've have the check hybrid come on and for me to reset the codes I had to unplug the 12v for at least 30 seconds
     
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  8. Michael48

    Michael48 Junior Member

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    I bought the car from Enterprise Rental with 43k miles on it just over a year ago. I have put over 100k miles on it since then. I know my scan device, Verizon Delphi with App, is not the definitive device to use but at the time, it was the only thing available to me. I went more with the fact that the battery drained too fast under load and my dealer wanted me to wait two weeks for an appointment. I was working two jobs at the time so time was a luxury I didn't have and went with the hail mary try of replacing the battery. I didn't mean to imply that this was always going to be the fix, just that it is a possible answer. More of an FYI I felt should be shared.
     
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