NOT Normal P Lock Malfunction - ONLY Happens Over 80 Degrees. Never When Cooler

Yes, pin to ground and both connectors disconnected.

I think I get what you're saying but maybe not. The wiring chart on page 262 shows H17-9 going directly to T4-7 and I didn't see it doing anything else (but I could have missed it.) In that case, your theory makes sense. But the H17-10 seems to connect to a lot of different things, so it seems plausible that there's supposed to be a high resistance because of some device in that circuit. And since it's low, it seems that indicated that the current would be bleeding off to ground, hence the low resistance and the P lock error. That's just my shade tree mechanic logic. Maybe it's not true. Whatever the reason, I assume Toyota knows what it should be.

I'll redo those tests today and see if I get the same results.

 

OK thanks maybe I'll be able to find it. I know roughly where it should be and I see the shape of it on page 384.

I just saw the drawing of a junction connector. It's feasible that one of the "short terminals" is the problem. Maybe I can open up the connector and see them and tell if any are bad.

 

I couldn't find the J14 connector. It must be behind the AC vent box and I didn't want to take that all apart.

I did the
PCON (H17–9) or PCON (T4–7) – Body ground
PPOS (H17–10) or PPOS (T4–8) – Body ground
tests again and had zero ohms on all of them. (Supposed to be 10kOhms or higher.)

I used a few different ground points just to be sure and it all came out the same as before. BUT I just learned that I've been misreading my meter. It read "OL" which I was interpreting as zero. The meter's manual says that means "the input is too large for the selected range." The meter reads MegaOhms so hard to believe that the resistance is beyond that. Maybe that's a sign of something.

Then I plugged in one connector and did the test on the other one's pins, and vice versa. That changed things.Those actually did show 0.00 ohms. But since the connector is plugged in, that's against the diagnostic instructions. Maybe it means something. Also when doing that there were pulses of resistance apparently. I think it would go blank and then back to 0.00.

So if those OL readings mean mega mega resistance, that's over the 10k it calls for so maybe it's not the cables after all.

 

After the above testing...Today was 88 degrees and 90% humidity. I ran the car in the driveway with the AC cranked, planning to drive and see if I got the P lock error. After sitting there 5 minutes in the cold air and not even putting the car in gear, the P lock error came.

Maybe it's a clue that the car doesn't even have to be in gear or driving to get the error?

That still keeps me thinking that the problem is on the engine side of the firewall. It didn't happen instantly, so perhaps five minutes of engine heat is all that was needed to put it into error mode. But on the flip side, when it was 78 degrees I ran the 140 degree hair dryer on all of the wires and components I could get to and didn't get the error, so maybe not. Or maybe I just didn't get the hot air in the right place for long enough.

I inspected all the wires along the firewall again and didn't see any damaged ones. There's plenty of places where the squirrels have eaten the insulation off the hood and firewall, but I didn't see or feel any damaged wires. Still could be though.

The P3102 diagnostic says these are the trouble areas:
Wire harness or connector
Transmission control ECU
HV control ECU
Power source control ECU

Power source control ECU seems to be above the steering wheel on the firewall. Potentially getting hot from the missing firewall insulation?
HV control ECU is to the right of the glovebox close to the body. Potential radiant heat from outside getting to it?
I did run the hair dryer on/near them for a couple of minutes when it was cooler and didn't get the P lock error so maybe not.

I'm running out of ideas for what it could be. Maybe I just need to start replacing ECUs.