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

Rock_Star · May 25, 2024

2008 Prius 248,000 miles. I've checked all the fixes that I could find on PriusChat, but none help.

In spring 2021 I got the P lock error for the first time. Error code P3102. I reset the codes a few times over the summer and continued on. No issues once it got cooler in the autumn and winter.

Then it happened again off and on in summer 2022, summer 2023, and just started again in 2024 once it got into the 80s. Again, it never happens when the weather is cooler.

I had an Optima Yellow Top in the car originally. It tested fine, but people here said that the P lock issue was probably caused by a bad battery.

So I replace it with a genuine Toyota battery. It didn't fix the issue--still P lock errors when it got hot. Within a year, the Toyota battery was bad--only 12.2V after being on the charger multiple times. (Toyota wouldn't honor the warranty and replace it. They said it had to test below 12v for them to consider it bad, even though every mechanic at the dealership knows it needs to be above 12.6V to work properly. So I was done with Toyota batteries.)

I replaced the Toyota battery with one from Walmart about 3 months ago. Its volt level is fine, yet the P lock problems started again once it got hot a couple of weeks ago. After 3 different batteries not fixing the issue, I'm sure it's not a battery problem. Also, when the car is on, it's putting 13.88V into the battery so it keeps the battery charged.

Voltage of the 7.5A P con main fuse has 13.88V (on both sides) when the car is on, and even with the P lock error happening, so it's not that.

Pin 13 on the TCU plug behind the glove box also has 13.88V so it's not that either.

Wires going into the shift actuator seem fine.

Since this issue only happens when it's hot, and I know that heat increases electrical resistance, I assume that some wire or sensor is getting too hot during hot weather, the resistance gets too high, so I get the P lock error. And this is why I don't have the issue below 80 degrees. If it's 86 degrees or hotter, the error comes on within seconds of the ICE starting. If it's 80~ degrees, sometimes I can drive without errors, but other times in 15-30 minutes the error will occur. And if it's something like 80 degrees and the car ran without error, but I park on a hot asphalt parking lot, when I come out and start my car, the error comes immediately. (Sometimes the Prius outside temp gauge shows over 100 degrees in this case from the radiant heat)

So for all of those reasons, I think it's definitely heat-related. But what?

Rodents ate some car wires last fall. I fixed all I could find, but that's a possibility. Maybe they ate some insulation off a wire so that radiant heat affects it. But which wire? However, this problem started three years before I had rodent issues, and didn't happen at all when it was cooler even after the rodent issue, so maybe it's not that.

Any ideas? Thanks!

bisco · May 25, 2024

sounds like you need a scanner that will reveal the sub codes:

2007-gen2-prius-ongoing-nightmare-problem-w-p-mechanism-hv-code-p3102.242762

Tombukt2 · May 25, 2024

So when the p lock error is happening You still have the 12 volts of battery voltage coming out of the white plug that plugs into the white receptacle in the very top of the battery the mysterious blue wire that seems to run out of that plug when it's plugged into the fuse box goes down to the side of the fuse box over into the harness where it tees like it's going to go down under the crankshaft or something and then the plug into a crank or cam sensor timing chain sensor something like that? I do know that that skinny blue wire on the back side underneath the fuse box it becomes a still skinny blue wire but it has silver dots on the wire and it just rares around and goes somewhere into the cabin I have to take the windshield out of this parts car so I can lean over and look and see where this blue wire goes when it goes into the cabin just impossible to see and rummage around in there with the windshield in place.

Rock_Star · May 27, 2024

bisco said: ↑

sounds like you need a scanner that will reveal the sub codes:

2007-gen2-prius-ongoing-nightmare-problem-w-p-mechanism-hv-code-p3102.242762
Click to expand...

I'll look into that. Mine only shows the top level ones apparently.

Rock_Star · May 27, 2024

Tombukt2 said: ↑

So when the p lock error is happening You still have the 12 volts of battery voltage coming out of the white plug that plugs into the white receptacle in the very top of the battery the mysterious blue wire that seems to run out of that plug when it's plugged into the fuse box goes down to the side of the fuse box over into the harness where it tees like it's going to go down under the crankshaft or something and then the plug into a crank or cam sensor timing chain sensor something like that? I do know that that skinny blue wire on the back side underneath the fuse box it becomes a still skinny blue wire but it has silver dots on the wire and it just rares around and goes somewhere into the cabin I have to take the windshield out of this parts car so I can lean over and look and see where this blue wire goes when it goes into the cabin just impossible to see and rummage around in there with the windshield in place.
Click to expand...

Sorry, but I'm not following what you're saying. Are you telling me to check for voltage on a specific wire?

Tombukt2 · May 27, 2024

Yes when you're experiencing the pealock problem while you're in the midst of it on the wire that's blue that's in the top of the fuse box that's in the white plug that plugs into the white receptacle in the very top of the fuse box that blue wire the fourth one over on the very top row of wires in that plug is a blue wire what happens is apparently this circuit loses 12 volts from somewhere you'll measure it and it'll be like 6 volts 0.6 volts 4 volts weird numbers people run a jumper wire from that blue wire down to the 7.5 amp p lock fuse I think that's what the rating of that fuse is. And then that restores the 12 volts and the p-lock malfunction goes away. So when you are in your throes of the plock malfunction. Do you have a full 12 volts on that wire coming out of that plug The blue wire fourth one over That's the one that everybody's having problems with usually when they're having the p lock malfunction You can read about it in other threads I was just curious if during your troubles with the P-Lock issue are you having still the 12 volts on that blue wire that blue wire takes off goes down from that plug and over to the harness and looks like it goes down to the bottom of the engine where it may connect to crank or camshaft sensors or something. Then the blue wire from under the fuse box is blue with silver circles on it and goes into the cabin but until I get the windshield out of this parts car I can't reach my hands and lights in there and find where that blue wire goes and what it goes to that would be losing 12 volts and creating the p lock problem.

Rock_Star · May 28, 2024

Tombukt2 said: ↑

Yes when you're experiencing the pealock problem while you're in the midst of it on the wire that's blue that's in the top of the fuse box that's in the white plug that plugs into the white receptacle in the very top of the fuse box that blue wire the fourth one over on the very top row of wires in that plug is a blue wire what happens is apparently this circuit loses 12 volts from somewhere you'll measure it and it'll be like 6 volts 0.6 volts 4 volts weird numbers people run a jumper wire from that blue wire down to the 7.5 amp p lock fuse I think that's what the rating of that fuse is. And then that restores the 12 volts and the p-lock malfunction goes away. So when you are in your throes of the plock malfunction. Do you have a full 12 volts on that wire coming out of that plug The blue wire fourth one over That's the one that everybody's having problems with usually when they're having the p lock malfunction You can read about it in other threads I was just curious if during your troubles with the P-Lock issue are you having still the 12 volts on that blue wire that blue wire takes off goes down from that plug and over to the harness and looks like it goes down to the bottom of the engine where it may connect to crank or camshaft sensors or something. Then the blue wire from under the fuse box is blue with silver circles on it and goes into the cabin but until I get the windshield out of this parts car I can't reach my hands and lights in there and find where that blue wire goes and what it goes to that would be losing 12 volts and creating the p lock problem.
Click to expand...

OK, I understand what you mean now.

Yes, I had a jumper from that 7.5A fuse to the blue wire above for the last three years and it didn't change anything--I still got the P-lock error. I guess it's possible that I didn't make a good connection with it and that's why it didn't work.

A few days ago I removed the jumper because it wasn't helping. I think I checked that blue wire terminal before I removed it and it was still at 12+V with or without the jumper, but now I'm not 100% certain. I don't have the P-lock error now because the weather is cooler, but I'll check the voltage on that blue wire if/when the error comes back again.

Are you saying the 12V power comes FROM the blue wire with silver circles below the fuse box, through the connector, and into the blue wire on top? If that's the case, are you also saying maybe it's the blue wire with silver circles below the fuse box that's actually failing? I think there's a thread that mentions a fuse in the fuse panel above the driver's left leg and to the left of the steering wheel that could also be involved with that circuit. Maybe that's where the blue wire with silver circles goes. I think I checked that fuse a few years ago and it was fine, but it's possible that I'm thinking of trying to fix another issue.

Rock_Star · May 28, 2024

Tombukt2 said: ↑

Yes when you're experiencing the pealock problem while you're in the midst of it on the wire that's blue that's in the top of the fuse box that's in the white plug that plugs into the white receptacle in the very top of the fuse box that blue wire the fourth one over on the very top row of wires in that plug is a blue wire what happens is apparently this circuit loses 12 volts from somewhere you'll measure it and it'll be like 6 volts 0.6 volts 4 volts weird numbers people run a jumper wire from that blue wire down to the 7.5 amp p lock fuse I think that's what the rating of that fuse is. And then that restores the 12 volts and the p-lock malfunction goes away. So when you are in your throes of the plock malfunction. Do you have a full 12 volts on that wire coming out of that plug The blue wire fourth one over That's the one that everybody's having problems with usually when they're having the p lock malfunction You can read about it in other threads I was just curious if during your troubles with the P-Lock issue are you having still the 12 volts on that blue wire that blue wire takes off goes down from that plug and over to the harness and looks like it goes down to the bottom of the engine where it may connect to crank or camshaft sensors or something. Then the blue wire from under the fuse box is blue with silver circles on it and goes into the cabin but until I get the windshield out of this parts car I can't reach my hands and lights in there and find where that blue wire goes and what it goes to that would be losing 12 volts and creating the p lock problem.
Click to expand...

The P-lock error came back today when the temperature got hot again.

I checked the blue wire that you talked about and it has 13.88V even when the P-lock errror is happening, so that's not the issue.

Tombukt2 · May 29, 2024

If you look on YouTube I'm going to look again today and try to find it there is a video of some Russian guys with a generation 2 Prius with the P-Lock error going on in the video this is a repair shop and they show them using a version of Toyota tec software. And the version of the software they're using is English and while the video is running you can see the Russian guys looking at the English version of the repair manual dealing with the p lock error now I can't understand all of what they're saying because my Russian is limited from the Cold war days but basically what they wind up doing is lifting the car up and looking at a wiring harness that looks like it goes under the crankshaft pulley and over to the crankshaft or camshaft or some kind of timing sensor over on that side of the engine and when they undo the wrap that's on the harness they either find some burned wires or some wires that have been rubbed by something and then it shows them soldering some wires together in that harness that I guess were rubbed apart or what have you and when they do that the p.lock error goes away. Well certainly quite interesting and something in this Toyota software for this code told them to be looking at the wiring that goes to the position sensor over on that side of the engine because if something is wrong with what that wiring is seeing the lock code will be there That's what I gathered from it It was quite interesting to watch.

Rock_Star · May 29, 2024

Tombukt2 said: ↑

If you look on YouTube I'm going to look again today and try to find it there is a video of some Russian guys with a generation 2 Prius with the P-Lock error going on in the video this is a repair shop and they show them using a version of Toyota tec software. And the version of the software they're using is English and while the video is running you can see the Russian guys looking at the English version of the repair manual dealing with the p lock error now I can't understand all of what they're saying because my Russian is limited from the Cold war days but basically what they wind up doing is lifting the car up and looking at a wiring harness that looks like it goes under the crankshaft pulley and over to the crankshaft or camshaft or some kind of timing sensor over on that side of the engine and when they undo the wrap that's on the harness they either find some burned wires or some wires that have been rubbed by something and then it shows them soldering some wires together in that harness that I guess were rubbed apart or what have you and when they do that the p.lock error goes away. Well certainly quite interesting and something in this Toyota software for this code told them to be looking at the wiring that goes to the position sensor over on that side of the engine because if something is wrong with what that wiring is seeing the lock code will be there That's what I gathered from it It was quite interesting to watch.
Click to expand...

I've searched youtube for 30 minutes and I can't find the video you mentioned. Please send me the link if you find it.

I'm also leaning towards it being a damaged wire.
I can't really understand where exactly the wire is you're talking about. Do you think you could look at this Prius wiring doc and maybe tell me which wire they fixed?

https://f01.justanswer.com/El_Jared/d9ca3293-744a-4baa-8b9c-a097c86e1d58_prius_component_loc.pdf

I took the car to my buddy's shop and his Autel scanner only showed the P3102 error like my scanner does. Someone above linked to a thread which said that the Autel Maxi AP200 could show the sub codes so I'm going to look into getting that to see if it give me more info. Also in that thread they said there's one that's almost as good as the Toyota scanner but I think it's a lot more expensive.

But if you can tell me which wire to look at that would probably be a lot easier to figure out. Thanks!

Tombukt2 · May 30, 2024

If you go out and look right underneath your crankshaft pulley you'll see a wire loom I do believe that runs under the crank pulley this is where the Russian guys were working I will try and find that link today It was pretty cool they had the car on a lift so they could see this wiring harness really easily laying on the ground you can see it easily too It goes in curves right under the crank pulley that's the thing that has the belt on it for the water pump

Tombukt2 · May 30, 2024

I have an '05 that's up on jack stands it's being ripped to pieces I'll go out and take a picture later this morning of the area these guys in the video are working on there's a wire loom like I say that goes right under the crankshaft pulley I do believe you can't really miss it You have to take the clips down and get it to hang down wire and goes from the circuit that runs the P-Lock mechanism from a crank or cam position sensor that's over on what would be the firewall side of the engine and it comes from the radiator side of the engine or that blue wire comes across the transmission I believe it goes under the inverter or along side of it this wire loom then it hits this t in the wire loom that runs up over the valve cover or drops down towards the air conditioning hoses in the side of the motor and then crosses under the crankshaft pulley to reach the sensors that are on the firewall side of the engine I believe that thin blue wire will wind up over there to detect some type of position of something to allow the p lock to stay off or on

Rock_Star · May 30, 2024

Tombukt2 said: ↑

I have an '05 that's up on jack stands it's being ripped to pieces I'll go out and take a picture later this morning of the area these guys in the video are working on there's a wire loom like I say that goes right under the crankshaft pulley I do believe you can't really miss it You have to take the clips down and get it to hang down wire and goes from the circuit that runs the P-Lock mechanism from a crank or cam position sensor that's over on what would be the firewall side of the engine and it comes from the radiator side of the engine or that blue wire comes across the transmission I believe it goes under the inverter or along side of it this wire loom then it hits this t in the wire loom that runs up over the valve cover or drops down towards the air conditioning hoses in the side of the motor and then crosses under the crankshaft pulley to reach the sensors that are on the firewall side of the engine I believe that thin blue wire will wind up over there to detect some type of position of something to allow the p lock to stay off or on
Click to expand...

Good info. Thanks!

I'll crawl under the car tomorrow and see if I can get to it.

Rock_Star · May 31, 2024

Tombukt2 said: ↑

If you go out and look right underneath your crankshaft pulley you'll see a wire loom I do believe that runs under the crank pulley this is where the Russian guys were working I will try and find that link today It was pretty cool they had the car on a lift so they could see this wiring harness really easily laying on the ground you can see it easily too It goes in curves right under the crank pulley that's the thing that has the belt on it for the water pump
Click to expand...

I found the wire you were talking about. I pulled about 6 inches of wire out of the plastic protection shroud but I saw no damage. I couldn't get my hands on any more of it, but I couldn't see any damage to the plastic shroud so I'm assuming that the wire inside it is OK. I also inspected every wire I could find from above and below and I didn't see any damage. I unplugged that wire and sprayed electrical contact cleaner on the plug and sensor, so I had minor hope that would fix it. It didn't.

I drove it after that and it was fine driving at 82 degrees outside temperature. When I came out of the place, after sitting on the hot asphalt, the Prius said it was 89 degrees. The P-lock warning came on as soon as the ICE started, so it's the same ole problem.

Tomorrow the Autel Maxi AP200 will be delivered so hopefully, it will tell me a subcode that will lead me in the right direction.

pasadena_commut · May 31, 2024

Perhaps try blowing cold air at various locations in the engine bay and under the car when it is malfunctioning, or try blowing hot air when it should be working. If you can "flip the state" this way it could let you find the temperature sensitive spot. Probably easier to do the latter - just use a hair dryer (NOT a heat gun). Duster in a can products blow cold and usually have nonflammable propellants. The cold gas produced probably doesn't have enough heat capacity to cool a big chunk of metal, but it should be able to cool a wire bundle fairly quickly. Downside is it may cause condensation or possibly even frost pretty quickly.

Edit: what is probably going on is that the expansion with increased temperature is just enough to make an electrical connection somewhere, and that breaks P lock. Seems pretty unlikely that it is a mechanical issue.

Rock_Star · May 31, 2024

pasadena_commut said: ↑

Perhaps try blowing cold air at various locations in the engine bay and under the car when it is malfunctioning, or try blowing hot air when it should be working. If you can "flip the state" this way it could let you find the temperature sensitive spot. Probably easier to do the latter - just use a hair dryer (NOT a heat gun). Duster in a can products blow cold and usually have nonflammable propellants. The cold gas produced probably doesn't have enough heat capacity to cool a big chunk of metal, but it should be able to cool a wire bundle fairly quickly. Downside is it may cause condensation or possibly even frost pretty quickly.

Edit: what is probably going on is that the expansion with increased temperature is just enough to make an electrical connection somewhere, and that breaks P lock. Seems pretty unlikely that it is a mechanical issue.
Click to expand...

One of my mechanic friends also suggested using a hair dryer to try and find the issue, so we may do that later this week. Looks like rain here for the next several days or I could do it myself.

RE: "increased temperature is just enough to make an electrical connection somewhere"
Are you thinking that a wire connector/plug is defective and the heat shorts it out or something? If not the connectors, I guess try and heat up along the length of all of the cables and hope I can set off the issue?

pasadena_commut · Jun 1, 2024

Rock_Star said: ↑

Are you thinking that a wire connector/plug is defective and the heat shorts it out or something? If not the connectors, I guess try and heat up along the length of all of the cables and hope I can set off the issue?
Click to expand...

I suspect a wire has lost its insulation (from rubbing or rodents or overheating or whatever) and above the right temperature it touches some chunk of metal which is at ground and the P-lock code appears. Alternatively, two pins in a socket/connector may only be in the most tenuous of contact, possibly from not being fully inserted, and heating up the connector causes the plastic to expand which separates them.

It doesn't have to be wires. Circuit boards can go bad such that they don't work above certain temperatures.

Rock_Star · Jun 1, 2024

pasadena_commut said: ↑

I suspect a wire has lost its insulation (from rubbing or rodents or overheating or whatever) and above the right temperature it touches some chunk of metal which is at ground and the P-lock code appears. Alternatively, two pins in a socket/connector may only be in the most tenuous of contact, possibly from not being fully inserted, and heating up the connector causes the plastic to expand which separates them.

It doesn't have to be wires. Circuit boards can go bad such that they don't work above certain temperatures.
Click to expand...

You'd think that a damaged wire would be visible but I can't find any that look bad. (Other than the eight wires to the right headlight that the rodents ate a few months ago. I've repaired those and the lights work fine. And, this P-lock error started happening 2.5 years before I saw any rodent damage.)

Or perhaps some insulation burned off over time from engine heat and it's still within the plastic shroud so it's not visible.

I've examined every connector that I can find and I don't see any damage or loose wires. I've removed the ones that I can, and I've sprayed them with contact cleaner, just in case. No luck so far.

Perhaps the hair dryer trick may be the only way to isolate where the issue is.

Rock_Star · Jun 1, 2024

I got the Autel Maxi AP200 and it gave me the subcodes (and another code) that my previous reader didn't show.

Error Codes:

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

I found this video about that exact error and subcode, but I think it's in Turkish so I don't know what to make of it. I can mostly see the wires they're messing with but I don't understand what the fix was.

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

I haven't found anything yet about that possible fix. 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.

The scanner allowed me to save PDFs of the complete error report data (several screens worth) but I can't find where it saved them or I'd upload them.

Rock_Star · Jun 1, 2024

Other things suggested on PriusChat that I checked today. None were the issue.

"Check the P CON relay condition. Remove the relay and use an ohmmeter to find the relay coil terminals (should be ~100 ohms or so.) Apply 12VDC across those terminals. Measure the resistance across the switched terminals, which should be less than 0.5 ohms"

I checked voltage and resistance on the relevant Transmission ECU and PCON harnesses, as per this Diagnostic from Toyota
https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/repair%20manual/04pruisr/05/21bpm/3102524.pdf

Since those things checked out as per the diagnostic procedure for P3102. Detail code 2: 581, the next thing it says is:
"REPLACE HV CONTROL ECU, TRANSMISSION CONTROL ECU AND POWER SOURCE CONTROL ECU"

I think every thread I've read here says people replaced those things and it didn't fix the problem so it doesn't seem logical to do that. I'm sure they're pretty expensive parts.

I read this today "There have been reports of the resolver plug on the front side of the trans failing due to corrosion."
I assume that's the M9 plug on the front left side of the transmission. Last September a rodent chewed through a wire to it and it gave a P0A40/41 error. We fixed the wire, cleaned the sensor and plug, and all the wires looked good. Of course, it's possible that something else is wrong with it. (But these P lock issues started 2.5 years before the rodent issues, so it could be unrelated or coincidental.)

Any other things that I can check?

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

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

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