"There is a problem with the Transmission P Lock mechanism" when road is wet

I'm having the same issue in wet weather. See /!\ Caution The transmission P lock mechanism is abnormal | PriusChat

A weak 12 v battery can bring about this error as many threads report. Seems the parking pawl is deployed by a motor. If doesn't move fast enough the ECU thinks it might be bad. Obviously that's not your problem.

This thread reported success by jumping the transmission ECU power wire which seems hard to believe. I would expect the problem to be with the sense wire as its wet related. See Red Triangle, no DTC, car drives fine? | PriusChat

I've been good for a few months, but today we had a big melt and everything is wet. If I solve this I'll post in my thread above.

Take a look at this luscious garage video. Notice that flex circuit that has the Hall sensors on it.

. I wonder if that puppy's getting wet.

 

I saw that warning in a Prius that just had it's transmission replaced. I traced the problem to the plug on park control motor being loose. I recommend removing the plug and spray some contact cleaner. Then look for any likely spots for water getting in to.
Brad

 

Sorry to resurrect such an old thread.
I have an 06 prius with 245k miles thats been throwing the "Caution The transmission P lock mechanism is abnormal" code on and off whenever I drive in the wet, as in beeping numerous times during the drive, really its great I've looked at the thread where one guy suggests jumping a wire in the ecu under the passenger dashboard, but that doesn't make much sense to me as that part of the car is more or less shielded from the elements and humidity. Brad, would you be able to give me some direction in finding the plug you suggest cleaning out? Oh, forgot to mention, I just installed a brand new optima yellow top battery which hasn't helped the problem, and its been doing this, albeit less often for over a year now. Thanks for the responses guys!

 

Mike, I think moisture gets into the shift actuator and shorts out the hall sensors on the circuit board. Fortunately the car operates the motor anyway, but you get the warning and serenade of beeps. I bought a used shift actuator off eBay for $50 but didn't get it installed. I gave it to the guy who bought the car who also had access to a lift. I know he's using the car, but I don't know if the p lock was fixed.

 

Also sorry to resurrect this thread, but did anyone get confirmation on any of these hypotheses? I have been searching for months and finally found this thread which fits with what I'm seeing. First started when drove through flash flooding and recurs when it's wet. Also seems to fluctuate or beep when there is more sudden braking or acceleration. Seems like it must be a connection of some sort. Otherwise drives fine. Heartstopping /!\ is a bit unnerving, but you get used to it.

 

My 2004 is doing the same thing now. Starting is fine. It's not until i start driving around in wet weather that this starts. The alarm becomes more frequent as your drive cycle continues.
I have been researching the P Con Main fuse ciruit online as the culprit. Being that its 15 degrees here in MI right now, I wont get the problem again until the snow thaw or when its wet outside.
Anyways, a quick check of the circuit at the 7.5 P Con Main fuse revealed gouges and indentation marks on each side of the fuse where the fuse block makes contact.
The second thing i noticed with my voltage meter, probing the "hot" side of that fuse spot, is that the top of the copper contact flexed and the voltage was racing up and down from 12.4 to 11.34 vdc. While the check on the lower part of the copper contact stayed at a consistent 12.4. Mind you, I did make sure the probe had good contact through out the flexing many times to comfirm its readings.
Im suspecting that the combination of the fuse and the copper fuse contact may have some blame to this. And maybe a wet condition is just enough to make the connection even worse while driving down the road.
I replaced the fuse hopeing that it will tighten the connection without the indentation or gouges. I'll have to wait till it warms up to see if this is enough.

 

Had a four day stretch within the past week of constistent wet rainy conditions above freezing and can say with confidence that the P Con Main fuse swap out worked. Have had no reocurrances of the P Lock Mechanism error in my driving during or after those four days. Prior to the fuse swap, the error would have most definitely showed multiple times each day.
I'll repost if the error returns.
Hope this helps someone.

 

Well, its been a few months since I last posted. The warning remained off for a couple of weeks through rain and snow. Ultimately it returned during wet weather. Kind of weird how it remained off durring that time.
Anyways, i had replaced my 12v battery a couple of weeks ago. It was definitely below the acceptible threshold during a prestart battery check. Hoping that would solve the p lock issue when it rains. I later found it did not.
Today was a nice day to wrench under the car, so i decided to tackle the shift actuator theory. I took a few pics for everyone, being it doesn't seem anyone here has posted the actual job being done.
It took me 4 hrs to do, due in part to taking the shift actuator back off three times to adjust the stater inside. The car wouldn't start at all with /!\ and p lock message. Also a popup on the screen with "problem". Had i had it set correctly the first time i figure it would have been a 2 hr job.
So i was able to access the shift actuator from underneath the drivers side and through the wheel well. Tight area. Had to turn the steering wheel to the right for more room. Its held on to the cvt with 3 T30 screws. The electrical connector was able to be shimmyed off with an awl pryed under the release tab and a flathead driver pushing up on the bottom of the connecter. Those T30 screws take time to take off. I used a small T30 bit to a universal 1/4 socket with an extention. Access is from behind the subframe. The top T30, I used a small ratched the could adapt to the T30 bit. No room for anything else.
Once off, i pulled the rubber seal and used dielectric grease to lubricate. I also applied the dielectric to the inside perimeter of the electical connector. And when back together, i applied more dielectric on the top of the exterior plug connector for good measure. Moisture should not be getting anywhere in this!
Tommorow has rain in the forcast. I'll update the results of this soon if its a fail, or later either way.

 

Its been less then a week since i did the work. Couple of rain storms, to include a 3 hour drive today in a non-stop torrential downpour with no /!\ . I'm feeling optimistic on this one. Keep all of you posted

 

16 days later........
I consider the last attempt a failure.

/!\ came back. Seemed to take longer this time for this to come back on though.

However, I did find the problem!
I went back to the drawing board with the circuit powering the TCU under the glove box from the P Con Main fuse. While previous attempts to check voltage at the TCU's pin #13 have checked good in the past (after triangle has gone back off), I decided to soak the engine wiring harness on the top firewall with water from a spray bottle to replicate the P lock condition. It took a day for it to soak in. And when it did, the P lock and triangle abnormally stayed on for days. I definitely festered the demon in this problem!
For diagnostics, this was perfect! Honestly i was thinking this was going to point more towards a grounding issue on the TCU.
2 pins to the left of #13 is the ground. That checked good. Then I performed the voltage check to pin 13....... Registered 0.46v ! Should be at least 12v. Ah ha moment! Theres a break in the circuit from pin 13 to the fuse box. I tried moving and adjusting the wiring harness to see fluctuations along the whole stretch. Hard to get to under he hood. I found only a 0.01 fluctuation to the right of the inverter strait feom the fuse box. I'm assuming the break is under the power inverter.
My fix: like what some have done. Provide the 12v from another source to pin 13 on the TCU. I wasn't picky. I probed the passenger kick panel area for connectors with 12v and spliced a wire to connect to pin 13.
So, the P Con Main fuse under the hood is now useless and an abandoned circuit.
Done! Triangle off! I'm done !

 

Hats off to you goodnuff for your persistence on solving this mystery! When I look at your photos, I see how tight is the area to remove the P-Lock Mechanism. I wonder if my big hands could have fit in there.

Seeing that younwere able to fix the problem by re-routing a 12V source to the ECU pin, now we know to keep our minds open to this being a possible cause.

Let us know if you see the problem pop up again.

 

Thanks for the writeup and great access pictures, will be needing these.

 

It's been almost a year and I'm glad to say I have had no /!\ since my last fix with the TCU pin 13 fix. Many of rain and snow storms. Hope this helps those who have the same symptoms.

 

I just want to say thanks for posting this fix. My 2007 Prius had exactly the same problem, intermittent at first, and then steady. I did a similar fix except I found this YouTube video and verified I too was missing the voltage right at the fuse box under the hood.

My P Con circuit read about 2.5 volts on the blue wire and had fairly high impedance back to the 7.5 amp fuse leg. I found another live circuit, put in a jumper right at the box connector, and the light is off. In my case, it must be the connection between the 7.5 amp fuse and the rest of the harness. Good luck to others who have a similar issue. Check the voltage on the circuit before you assume the problem is the same however.

 

I'm running into the same error message. I just checked the voltage using a multimeter, having set the dial to "20" (sorry if I sound like a total newbie -- that's exactly what I am!), on both sides of the 7.5 fuse and the readings fluctuated wildly, going from .78 to .25 (on both sides of the fuse). When I switched over to the blue wire, the numbers were similar, so there is power being supplied there right now. Which makes sense as my red triangle and error message is not showing right now.

I've only experienced this problem twice. I swapped out my battery this spring (it was time, over 5 years old, to another Optima) and the problem went away, but now the problem is back, so I think this is what I'm experiencing as well with the blue wire not getting power. But I'm leery of adding a wire from 7.5 to the blue wire in the fusebox, mainly because I have this question:

If the problem is intermittent (99% of the time, I don't have the error message), then if I were to add that wire, am I not supplying the TCU with twice the amount of power? Or am I thinking of this the wrong way? Thanks...

 

Folks, the numbers I reported are wildly inaccurate. A friend set me straight and it turns out I didn't have the ground touching the chassis properly. With the engine off, the reported voltage was right around 11.8V. So next time the red triangle and the error message comes up, I'll check the blue lead to see if it is indeed reporting a lower voltage.

 

Hey there, been doing a ton of research since this P Lock issue randomly happened to my car right after it was detailed. I suspect moisture got into this area somehow, but will double check tomorrow. I went out and bought a new battery which didnt fix it (which sucks, but the old one was like 8 years old so whatever). Going to test the voltage on these wires tomorrow. I don't believe in coincidences so i think the wetness of the car detailing screwed something up...

 

Yes, I've seen the video posted in #15 before, or even others like it. This seems to be a commonly-reported Gen 2 issue with that known solution right there at the fuse box.

 

@ goodnuff, thank you for your exquisite report! After reading your report and diagnosing with TechStream software a year and a half ago, I finally followed your instructions today and found the plug receiver cracked with corrosion around the pins.

IMG_8618 by DMajetich posted May 10, 2022 at 8:19 PM