I have not had this problem again since the last report. And I'm more confident that it was (is?) just an intermittent weirdness from high interior moisture. (My half-baked "theory" but the only one I have). So the rest of the half-baked theory story... I never found any actual water leaks to the interior. But what I did eventually figure out is that maybe I just need to keep the damned car clean? The "gutter" area around the trunk seal is pretty big and deep, which is cool b/c it can channel a lot of water. But it also likes to collect debris. When the COVID crap went down, it was easy for me to shift to remote work and stay home. So I did. I live on a heavily wooded lot, and not using the car very much (and even then rarely going into the trunk in any case) the car got pretty grungy sitting around under the trees. So one day I decided to give it a good cleaning. That trunk gutter was stuffed full of crap - shards of tree bark, twigs. leaves. It makes like a big sponge. It wasn't "leaking" to the point that my trunk was wet. But it was a route for moisture to make it inside. But I still have to wait until next summer too. By my half-baked theory, I need both hot and humid weather and heavy rain. I'm in Central VA, so we get some fat rain once in a while through fall and winter. But no hot and humid weather until summer. If I think of it I'll update. Another "seasonal affliction" is my P0420 (cat below efficiency). I've had the car like 4 years. Every winter it starts throwing that code, and then only during interstate driving (60-70+ mph). Come spring I can clear it and it won't come back until winter... Or I can not bother to clear it and it clears on its own. Or it can be winter and I stay off the interstate driving and stays away. There's some half-baked theory that could go into that too - cold weather fuel mixes are richer. So a cat nearing it's inability to do its work might do that. But seriously? Not for 4 years in a row. If it's on its way out, then it's on its way out. I guess I'm just saying that I do trust the computers and their error monitoring...but with a grain of salt. In any case, @Stock808, be very careful about equating your P3009 issue with mine. If you have a car just plain throwing a triangle and P3009, then that's not the same thing. And it's not something to take lightly. Mine would randomly pop up and then magically just ... poof ... disappear and not come back - for like a year. But I haven't seen it now for like 6 mos. I'll see what happens in 6 mos. In the meantime, I've now only got a "temporary" P0420 set...because it's wintertime. And I've been on the interstates lately.
I'm pleased to have report once I cleared the codes, made sure all the connectors to the HV Battery is snug and I even cleaned out the duct work (very dusty and gross). It has not since come back and the car is driven daily. I was afraid it was my transmission since my battery is a newer Dorman Reman battery Again this only came up when a heavy rain storm was just pounding on the car and I think the high humidity created a ground somewhere that's not present when its under normal operating conditions.
Just time for the yearly report. We had a very dry spring and early summer. Then a huge round of rain followed by high humidity. Then I got the P3009 again. The last time was last summer at my lat report. No good details. Still no signs of leaks to the interior. Soon after all the rain and the code I had to go out of town for a week so the car wasn't driven (left the 12V disconnected). During that time there was high humidity and daily thunderstorms. Came home yesterday and we hit a period of lower humidity today. I aired out the car, drove it today (ample time for code setting) and got nothing. That's it. The yearly appearing/disappearing P3009. I put a tub of "Damp Rid" in the trunk. Probably means nothing, but can't hurt anything. I have the random P3009 in the summer and the less-random P0420 in the winter (but only on the highway). So just an update if it helps anyone, Tho' IDK why it would since it answers no questions.
Just updating this post for the last time since I recently sold this car. I never did come up with anything definitive. And that's all I've got... I drove the car and 99% of the time it threw no errors at me. Once in a while in hot/humid/rainy weather it would throw a triangle and P3009 at me. One of the last times, I didn't have my code reader with me. And by the time I got home where it was (15 mile round trip or so) the triangle was gone and no codes. So, IDK. Maybe it was the P3009. Maybe not. But I'm sticking with my half-baked guess - that humidity and temp variations created some manner of short-lived condensation that evaporated once the hybrid pack got warm enough to basically burn it off. Plausible? IDK. But it's all I've got. But I went with it for 5 yrs and only had the P3009 during the humid/rainy summer weather. And even then, not consistent. For those searching, wish I could give you more info.
Must of missed this thread when I was dealing with my own P3009 issues back in November/January. Very different weather conditions (Eastern WA is a lot more dry than seattle) but iirc a similar theory of mine is that the times it happened was also more humid. Both codes happened when I was in a drive through late in the evening, and when the second one happened i caved due to being unable to replicate it and went and got the car looked at. No 3rd party mechanic around here would touch it and toyota never responded to my calls so I took it to a Honda dealer that had a Toyota master tech that worked there. They got the battery out and found a good chunk of corrosion on the terminals. Was quoted... $600+labor? For a new wiring harness, or they said they could clean the terminals and call it a day, which is what I chose. $800 total to get the battery out, harness cleaned/sealed, and reinstalled. Haven't had any issues the last 6 months. I also get the P0420 code, only in the winter, only on the freeway. Current thought is replacing the O2 sensor but honestly I probably wont bother unless I go back to doing a lot of freeway driving.
That is some ugly corrosion! My reman battery pack was only a year or two in from install when I got my first P3009. I was thinking maybe some corrosion - but nothing like that! I never looked. It showed up briefly once a year and then left me alone. So I did the same. As for the P0420, first I graphed it out and never did see why it would have set. I've graphed plenty of up/downstream sensors with no P0420 and saw much worse "jiggle" on the downstream then I ever saw on this Prius. I did replace the upstream sensor thinking, why not? If it was being "lazy" that could matter. And it can't hurt to replace it. (Even though the normal idea would be the downstream sensor, but the 0420 just comes from comparing upstream to downstream). Anyway, it made no difference. I think I might have had a tiny exhaust leak under certain load conditions. Doesn't matter for me as now I'll never know.
