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

One weird thing I found today with the Autel Maxi AP200--error code B1421. Solar sensor circuit passenger side. Seems like that was within the Air Conditioner ECU section.

"The solar sensor, which is installed on the upper side of the instrument panel, detects sunlight and controls the air conditioning AUTO mode. The output voltage from the solar sensor varies in accordance with the amount of sunlight. When the sunlight increases, the output voltage increases. As the sunlight decreases, the output voltage decreases. The Air Conditioning Amplifier detects changes in the output voltage from the solar sensor." Read more: Code B1421 Toyota Solar Sensor Circuit Passenger Side

Is there any way that error could be setting off the P lock error? (The autel couldn't clear that error code so maybe it's real.)

On one of these threads, someone said "my solution was passenger door handle malfunction. I disconnected the good sized electrical plug behind the handle..."

Someone else said "Transmission fluid moisture buildup was causing a high voltage leak error code P to engage error"

So maybe something seemingly unrelated could cause these electrical issues. The prius does seem incredibly sensitive to electrical weirdness.

 

Someone else suggested installing a used shift actuator as a likely fix.

 

Yeah, I've checked everything suggested on these forums and elsewhere. It's clearly not one of the "easy" fixes. Most likely a hidden bad wire or connector as some have said.

Today the problem was the worst it's ever been. It happened at 74 degrees on a cloudy and rainy day which was the first time I've ever had the issue below 80 degrees. And even after the car sat for 90 minutes, I cleared the codes and they came right back before the ICU even fired up. Since the other day I was messing with that wire under the crank pully like you suggested, It seems likely that I made it worse doing that. That's where I'll start further investigation. I'm going to take it to my mechanic buddy this week and hope he can isolate the problem.

I appreciate the help you've offered!

 

Here's what I've tried lately...

It was 83 degrees today so I took a hair dryer blowing 140 degree hot air on EVERY WIRE I could see and held it there for a couple of minutes everywhere to let it get plenty hot. All the wires I could see from the top of the engine, below the engine, in the back of the car below the trunk, fuses, relays, connectors, transmission ECU, all of the wires near the glove box, the shift control actuator and wires--EVERYTHING. (Just realized I didn't try heating the wires below the steering wheel or center console. I'll try that tomorrow.)

And I never got the P-lock error. Normally it comes at around 84 degrees and above, so if 83 degree weather and 140 hot air blowing on the wires doesn't make it happen, I guess that heat alone is not the issue.

It was only 38% humidity today so I wondered if it's a combination of heat AND humidity that causes the error. It never happens in rainy weather and never below 80 degrees, and usually at 84+ degrees. But why would that be? Maybe heat causes expansion, and humid air is wet enough to cause a short, but dry air doesn't. Seems far-fetched, but perhaps possible.

I even went out driving for 20 minutes to get the engine and transmission hot but didn't get the error. I applied the hair dryer again when everything was hot and still didn't get the error.

What is it that's magic about 84~ degrees that causes the error? If it's not the wires and connectors, what they heck could it be?

 

Also, I've been smelling gas when I drive for the last month or so. It seemed worse when the P-lock error happened, but I couldn't figure out why. I thought maybe that caused something fuel-related to stay engaged.

Well, today I happened to see a drip in front of the right rear tire. I saw that a squirrel had gnawed a tiny hole in the plastic fuel line. So then I looked everywhere in that back section and saw teeth marks all over the place. They have gnawed a bunch of the undercoating below the spare tire well, brake components, other fuel line components, and what seems to be the stuff they seal the seams in the metal underbody. (Photos attached.)

I couldn't find any damaged wires. I also applied the hair dryer to everything back there as well but the P-lock error never happened. I wonder if there could be heat and humidity getting up into the car from where the squirrels ate away the metal joint sealers and affecting a wire up there?

Are there any wires back there that could cause the p-lock error if they ground or shorted?

 

Finally...I saw teeth marks on the white plastic covering over the orange high-voltage wires that run below the car on the driver's side from the hybrid battery to the front. I took off that plastic covering and saw that part of that orange wire has foam on it but the foam on the part coming out from the battery has either worn or been eaten away.

Surely that foam is not for heat protection. I don't know what it would be for.

But just in case, I put a bunch of fiberglass insulation around that whole section of the wire and put the white plastic back on it. Hopefully, that won't hurt anything.

I pulled off part of that plastic shroud and didn't see any wire damage. Now it's got me wondering if the squirrels ate a wire back there that's causing the P-lock error, but I can't find any damaged wire.

 

It makes sense that it would protect from something, but I don't know what. There's nothing up there around it, even with the plastic cover. As I said though, I put fiberglass insulation all around it, just in case.

Ok I'll measure the voltage like you said, next time I get the P lock error. I measured it today vs the 12v battery running and in standby. The voltage at the 12v battery is pretty consistently 0.05V less than at the front jump terminal. I don't know if that's normal or not.

Oddly enough, I went driving today when it was 86 degrees and didn't get the error. Normally I would have at that temperature. Maybe some of my messing around with everything under the sun fixed it, but I'm not hopeful.

I mentioned before that heat AND humidity is a new theory. Today it was only 34% humidity, despite the high heat. Tomorrow it will be near 90 and supposedly humid, so we'll see if the error happens then.

One other odd but plausible theory I came up with yesterday. For the past few years I've had this very thick hand-made quilt in the trunk, sitting right on top of where the hybrid battery is. It's about 18" thick so I wonder if that has been holding in a lot of heat in the battery causing electrical issues. Yesterday I moved it to the back seat and today no error, despite the high heat. If I don't get the error tomorrow I'll put the quilt back in the trunk and measure the battery temp with Dr. Prius. I also put some ribbon at the battery fan outlet to see if it actually blows. So far I haven't seen it, but I heard it may not blow until the battery gets to 130 degrees or so.

 

Today I took a drive down the highway. It was 88 degrees and 55% humidity. 15 minutes into the drive and no P lock error so I was hopeful because normally at the temperature I'd expect it. So I pulled onto a side street to test the blanket theory. I took it out of the back seat and put it in its normal place in the trunk on top of the battery. Not 15 seconds after I started driving, I got the P lock error! So I'm thinking to myself, this is crazy. How in the world could that happen?

(It also gave a C1310 256 code for the first time. That's in the ABS system. Makes me wonder if it's related to the TPMS sensor error that I've had since they installed these tires in March 2021. I assume they didn't put it on right when I got new tires. That orange TPMS dashboard icon has been on constantly since March 2021 and the P lock error started a few months later. Probably a coincidence, but maybe not. Started me wondering if it was the tires and/or that sensor or something ABS-related, getting hot that's causing or contributing to the P lock error!?!)

I went back home and deleted the error codes but they came right back. (Heat related I'm still thinking.) About an hour later after the car cooled off I deleted the codes.

Then I removed the blanket from the car and went for another drive. This time it was 90 degrees and 51% humidity. No P lock error in 10 minutes/6 miles driving down the highway. So I pulled into a gas station to turn around. As I was braking and slowing down to reenter the highway, the P lock error went off again. (The C1310 256 error didn't happen that time.)

So this got me thinking....both times it happened today I was driving slowly and was braking or had just been braking. I thought about other times it happens...mainly the first start of the day when backing out of the driveway on a hot day (foot on the brake) or starting the car in a hot parking lot (foot on the brake) so that seems like a potential pattern. It has also happened 10 or 15 minutes into a drive on a hot day so it's not always while braking, but I would have been braking a few minutes before.

If it is brake sensor-related, that could make sense. I've gotten the P lock error a few times backing out of the driveway. You'd think nothing could be that hot instantly to cause the error if it was engine or transmission-related or even from a wire near the engine getting too hot. There wouldn't be time for any of them to get hot.

I think there is a thread here where they talk about either the parking brake or the brake pedal sensor being defective and causing the P lock error so I'll have to look into that.

So it could be something INSIDE the car getting hot and causing the error. I hear it can get 140 degrees inside a locked car on a 90-degree day so that could be it. The car is parked in the woods so rarely gets direct sun on it but I'm sure it still gets plenty hot. During cold weather with the heat on I guess it doesn't get hot enough to cause the error. Yesterday I ran the 140-degree hair dryer along all the wires under the dash and didn't get the error, so maybe it's somewhere not under the dash or I missed the exact spot.

Another thing that makes it seem likely to be inside the car is that when you're driving, even on a 90-degree day, surely a 55 MPH wind running through the engine compartment and underneath would dissipate any heat.

I'm pretty sure the error has come before when I had the AC on, but maybe wherever the issue is, isn't getting cooled enough, quickly enough. I know I had the AC on for part of the first drive today, but I think I turned before I pulled over, moved the blanket around, and got the P lock error.

It's supposed to be between 90-96 for the next few days so I'm going to crank up the AC while in the driveway and not start driving until it's good and cool. If I don't get the error then I'll know I'm on the right track!

(I also thought about what you said about the doors-- I did open the rear right and trunk so those are variables too...maybe a loose wire in them.

 

I first moved the blanket from the backseat to the trunk, on top of the battery where it normally is and got the code 15 seconds later as I said. Then as a test I cleared the codes, completely removed the blanket from the car, and went for another drive. 10 minutes later I got the error so it's not the blanket.

I did the brake test as you mentioned and the error didn't go away. But I don't think it would go away on its own. I think you have to clear the codes.

I should mess with the parking brake pedal too for good measure, but since I did the AC test I don't think that's it.

It was 88 degrees today and only 35 degrees humidity. I ran the 140-degree hair dryer all under the dash again and around the 12v and hybrid batteries and didn't get the code.

Then I cranked the AC for 10 minutes in the driveway to make sure the inside was cool before driving. I drove for 10 minutes with the AC cranked and got the P lock error. So I guess it's not an internal wire or component issue. (And with low humidity, there goes my heat AND humidity combo theory.)

Clearly though the high heat causes the issue. I've had the hair dryer on every single wire, connector, and component inside, outside, around the engine, transmission, and rear of the car and that doesn't make the error happen.

So maybe it's a component or wire inside the engine or transmission that needs to reach a certain temperature to make the error. But what? I have had the hair dryer on the shift actuator for several minutes, but it could be that it's something inside that unit that's not getting hot enough with the hair dryer, but does get hot enough when the ambient temp is high. Still though, if that were the case, I'd think the air going around it when driving would keep it cool enough. But maybe at high air temps it can't get cool enough even with airflow.

 

Yep, I put the codes and subcodes in message #19.

P3102. Detail code 2: 581
System: Hybrid Control
Description: Transmission Control ECU

C2306. Detail Information3: 20
System: Transmission Control
Description: Open or short circuit in w phase

The live data recording shows all (3 I think) circuits being within 0.2 - 0.3 volts of each other (all 12.3 - 12.5v if I recall correctly.) I figured the w phase would have been super low to trigger that message, but it wasn't.

"W phase" seems specific, but I still haven't been able to find the fix.

 

Thanks. I didn't know about the translate function. But I can't understand what they're talking about either. I think other posts have mentioned a blue wire and a blue wire with stripes, so that may be what they're talking about. I already pulled back the plastic shroud around the wires below the crankshaft pulley that they were working on and it was fine in the 5" I was able to access.

Last week I checked the voltages and resistance of the wires as instructed in the diagnostics manual that I attached here. No luck, unfortunately.

If you get no errors, the last part of it says:
"REPLACE HV CONTROL ECU, TRANSMISSION CONTROL ECU AND POWER SOURCE
CONTROL ECU"

So maybe those are the next steps.

But first I will do a full battery test with the Dr. Prius app. My current OBD reader is only wifi, and when it's engaged, you can't reach the internet and so I can't pay for the app upgrades required. And stupidly, Dr Prius requires you to be hooked up to the OBD reader in order to pay for the upgrade. It's dumb that you can't just click a link and pay, but you can't.

I should have the new reader on Monday so I'll run all of the hybrid battery tests. I read that problems with it can cause random error codes so it's worth doing. All voltages and temps look good on the free part of the app, so it's probably not it, but who knows.

I saw posts about hybrid battery terminals getting corroded and then shorting with heat and humidity, so that may be the next thing to check.

Or just start replacing ECUs. I haven't priced them yet to know if it's worth doing just in case.

As always, thanks for your help with this!

 

My reader gives both freeze frame and live data. I assume the differences are self-explanatory, but not sure if one is better than the other at any particular time. And I don't know what the different phase windings are or mean. I was just looking for anything that seemed abnormal.

I just went out for a drive and got C2306 and a new one: C2300. I've attached the live and freeze frames from C2306. Thought I made a C2300 live but guess I didn't, so there's just the freeze frame of it.