2007 Gen2 Prius ongoing nightmare - Problem w/ P mechanism - HV code P3102

Hello Prius Chat,

This is a tale but I want to include all the info I can remember. I'm a big DIYer and I am at my wits end with this situation.

Long time lurker since getting our first Prius back in 2018. Loved it so much that when it came time to replace our other vehicle, we got a Prius.

2007 Prius gen ii bought back in April with 130k miles. Rigorous test drive and seemed perfect. Took it home and worked fine until the end of May, commuting and long trips. Put about 500 or so miles on it and then after a long weekend of no use, went out Monday morning and got the "Problem with P mechanism" error and could not shift to drive.

Quick research on that showed it was not a good error message to receive on these.

At first I was able to fix it by letting the car sit off for 15 minutes and trying again. When that stopped working I had to unplug the 12v battery for 30 mins, and then it would be good to go. For awhile it would only show up like once every other week. In early July it kicked on and this time would not go off. Left me stranded down the road from my house unable to move it.

Did the research and found 12v battery most likely cause. Went out and got a new one, replaced it myself, car started up and all was good. Drove it for a week and then the error came back, could not clear it again.

Got an OBD sensor, multimeter, and Dr. Prius app. Pulled codes P3000, P3102, and P0A80. Bad hybrid battery.

I work in tech so decided to try to fix the hybrid battery myself by replacing bad sections. It was tough but not too difficult in my opinion. Got refreshed battery back in. Prius ran for 2 days, coded out again with the P mechanism error, same codes.

Got a professional to replace the hybrid battery with a refurb. All codes cleared! Hallelujah! Test drive fine. Back to work for 3 days - warning lights come back on dash. Code P3102 is back. Transmission control module failure. Makes sense with the original issue so maybe it is two fold?

Replaced the TCM. Glorious working Prius for 2 whole days and then get the P mechanism error. Only started after the code and light reappeared for a few hours. Can't clear it or it comes right back. Can't shift car. Car won't go into ready - same as before but still only pulling code P3102.

Throughout this all I also replaced some fuses and only issue I noticed regularly is a parasitic drain on the 12v that was more than should be. In the beginning it would die on me after not driving dor 3+ days and would have to charge it. Noticed that even with Prius off, you could actually watch the voltage drop on the battery. Also noticed that it was not the original 12v, replaced in 2017. Even with the new battery this still occurs, but not always which makes no sense to me. If left sit for a few days even the new battery will drop to <6 volts.

When the issue returned the latest time, the first thing I checked was the 12v battery and voltage was actually fine at right around 12.5. Seems to charge fine when the car engine runs.

I don't know what to do next. I dont have the funds to have the car experimented on and I have seen horror stories of thousands in labor to diagnose this problem only to have it not Be fixed.

Can anyone help me out on what next steps might be here?

 

The hybrid battery itself is testing fine all around in all apps I've tried.

I have a Veepeak bluetooth scanner. When I check the freeze frame in Car Scanner app, it appears to work but the code shown is p0000. Does this mean my adaptor cannot read the INF codes?

I checked the page but it still isn't clear to me. What is the cheapest option I can get to scan those codes?

 

To update:

Had the 12v unplugged for the last 2 days while I backed away from the situation for a minute.

Plugged it up today and no codes, went right into ready mode. Engines fired up. Tested 12v at 12.3v before I started.

Let it idle for 30+ minutes and nothing. Took it for a 3 mile drive, parked and indled for another 10 mins. Got big in and as I was pulling away coded hit. P3102. Red exclamation in triangle, exclamation point in circle, and VSC light all on, little ribbon across the top of the screen with an exclamation point.

But I was able to drive it the 3 miles back and park it at home again. It did not yet do the "P lock mechanism error" but that is usually what comes soon after.

Interestingly enough it seems to drive better than fine when it is working, I just dont get it.