Gen1 with constant P3001 code but no other issues

Looking for help with an odd problem - I think. Have searched, but can't find a thread on this
I have a 2001 with 140K miles or so, purchased a few months ago because the only problem seemed to be the motive battery and I had an extra battery with only a couple of bad cells. Time got away on me so I purchased/installed a Falcon Hybrid rebuilt with Gen2 cells. Everything worked well for a while, but the car now throws a P3001 (battery ECU) code periodically. No other codes and everything seems to operate normally. 12v battery (apparently fairly new) shows 12.5v after the car is parked for a day. After clearing the code, it sometimes comes back immediately, sometimes after several miles of driving. No recognizable correlation to temperature or driving conditions. Have heard of temperature sensors causing the problem, but not sure where to go with troubleshooting and, there are no other codes. Any ideas? I can swap in the ECU from the other battery I have here, but was hoping for some way to isolate the issue first. BTW, using Torque Lite (Android) to read/clear codes.

 

Thanks very much for helping me out. Sorry for the slow response. Terrible internet service today and couldn’t even log in most of the time.
For pulling codes, I use a generic OBD2 to Blue-tooth adaptor and have the Torque Lite app on my Blu phone (Android). When I request the codes, all I get is the P3001. I used the same setup on the same vehicle before changing the traction battery – when there were a few more codes to see.
I'm not at home right now but will check all the connections again when I return.
BTW, Falcon Hybrid said the rebuilt battery would come without a battery ECU and I would have to transfer mine, but when the battery came with one installed, I didn't swap them, thinking the one from Falcon was just as likely to be good as the one from the failed battery that came with the car.
Thanks again for your help.

 

Thanks for the advice, Brian. Noticed some chat about OBD2 readers, but most I saw referred to the hand-held devices. Looks like the Techstream software is freely available so long as one has the specialized cable. Too bad (for me) the software uses USB rather than blue-tooth. What version of the software are you using, or are the updates generally stable? I'll order a cable and check again. I have 3 old Priuses (Prii?) so will make good use of the tools.

 

Cable and software are supposed to arrive tomorrow. Should be able to scare up an old laptop to run the software.
Thanks again for all the guidance. And thanks for the suggestion to drive to Raymond. I think I'll try on my own a bit, first, but good to know there is someone who can help if needed.

 

Family interruption limited time this weekend and struggles with the Mini-VCI drivers kept me from getting any more information when the car was available. Will try again next weekend.

 

Update: Ended up with an unexpected 'short term' contract out of state (and country, actually). My daughter is the usual driver of this car and tolerated the error on the screen, paying attention to anything else the car did (or didn't do). Some time later (weeks, not hours or days), she started the car as usual, but got the normal display - and has not seen a code since. I am back home today and, yes, everything seems to be normal. Priui are amazing, but I didn't expect them to be self-healing Guessing whatever was unsettled is finally where it belongs. If something comes back, at least I have the tools now. Thanks again to all for your help.