06' Prius SOC at highway speeds

Dcrabtree, it sounds like your re-manufactured battery is going south. If you can get it replaced for nothing that's great. If not, imo, you should put a brand new battery in her, seeing that you've got such low mileage and it's been maintained properly. With a new hybrid battery, you should easily get another ten years out of your Prius...

 

Hi there,

Sounds to me like the HV battery is starting to fail, as that sounds very similar to what I experienced; rapid fluctuations between very high and very low charges (on flat terrain with consistent speed). About 2 weeks later, my HV battery failed (dash lit up like a Christmas tree and "Problem" appeared across top of MFD) and as a result had 4 cells replaced and I have been good as new ever since.

The good news is the car did NOT strand me, I could still get home, albeit a bit hobbled and little power once the electrical motor disengaged (had to reboot the car several times to get back to 'normal' mode).

3 different Toyota dealers quoted me a full replacement packs - over $3K with labour - but fortunately I found a private mechanic specializing in Prius who could rebuild the battery for me for a fraction of the cost...

 

My first disclaimer is I am in no way a Prius tech, so take what I say with a grain of salt.

Sorry to hear it is inconclusive, I am in a similar predicament with a mysterious red triangle which is not throwing any trouble codes and the car is otherwise driving fine (I put another thread on this -(Red Triangle, no DTC, car drives fine? | PriusChat).

My thought is that the problem is still your battery, it just hasn't reach a threshold low enough to trigger a fault. Like I mentioned earlier, I noticed this behaviour for a couple weeks before it finally failed. So you may need to wait it out for now. When I was with my mechanic and he had his computer hooked up to the car, he showed me the voltages on all the cells and it was clear a few of them were fluctuating quite wildly. Of course, this was after the failure, but I suspect it may have looked abnormal as well just prior, just not as much.... Again, just my opinion.

The good news though is if this is the same issue and the battery fails, your car will likely still be able to move, but you will want to get it to the shop as soon as you can to prevent any further damage due to failing cells.

Or I could be completely off base. Lol.

Good luck!

 

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I am not sure if you continue to experience this issue with unusual discharging or if a deeper issue has presented itself. I own a couple or Prius now, a Gen I my son drives with 180k miles on it and I drive a 2006 Gen II with 148k on it. I also buy these vehicles fix them and sell them. For a Gen II it is unusual for them to need a battery at 100k. Oh, I forgot to mention I live near Fort Worth, so am most familiar with vehicles that have experienced hot temperatures, which also impacts battery life. Certainly the Toyota dealers have the best equipment to scan and analyze the Prius battery and electronics. What they may not be exceptionally experienced with is diagnosing issues specific to Prius as they work on a broad range of Toyotas and the Prius has. Number of unique features. I agree of course those features span Prius, Camry, Highlander and even Avalons. They are also challenged to do a diagnosis quickly and move on so they make their paycheck. The very common issue for Gen II vehicles around this mileage that provides some unusual symptoms is the failure or beginning failure of the inverter coolant pump. It being an electric motor driven device, may begin to fail by slowing down or stopping intermittently. This causes the inverter to overheat slightly at first and confuses the electronics. When final failure occurs, it sets a code and check engine light, but causes all sorts of issues prior to that all which appear to be battery related. There are all sorts of posts on replacing and diagnosis of these pump failures. They are easy to replace if you just clamp off the hoses to it, one can change them and lose very little coolant in 30 to 45 minutes. I will say they run all the time if the car is in drive mode, so they do get a good bit of wear. Monitoring inverter temps and ensuring this pump is good as well as ensuring air flow through the battery pack is a good thing.