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

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

 

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.

 

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!

 

Not necessarily.

 

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

 

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