1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Problem with "P" Lock Mechanism

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by muddyjeff, Jul 5, 2019.

  1. muddyjeff

    muddyjeff New Member

    Joined:
    Jul 5, 2019
    3
    0
    0
    Location:
    Pittston, Maine
    Vehicle:
    2008 Prius
    Model:
    Base
    So let me begin be saying that I've read a lot of threads on this site regarding the problem with the P Lock mechanism and everyone says it's the battery. I ran through the instructions to test the battery using the multi-information display and it's within the parameters of being a good battery, so that's not an issue. I've been driving the car with this warning for about 5 years. At first, it would come on and off intermittently and was really annoying because of the beeping noise it makes when it comes on. Now it's on permanently.

    I was informed that it "could" be the transmission electronic control module by a Toyota dealer and they want around $2500 to replace it but would not guarantee that it would solve the issue, because something else could also be causing it, but they can't know for certain until this is replaced first. I did some researching of what it is, and it was a very simple replacement. I found a used one on eBay for about $25 and installed it in minutes.

    However, it didn't fix the issue. This could me two three things: 1) it was a bad part that I got; 2) I installed it incorrectly. Did I have to disconnect the battery first? Do I have to reset something after I install it? 3) There is someone else wrong with it.

    Any ideas? Thanks.

    Here's a pic of the Transmission ECM that I purchased. It has 3 screws that hold it in place and a single wire plug to connect it. Installs right under the glove box.
    [​IMG]
     
  2. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    24,906
    16,213
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    That ECU is the thing that announced the "problem with P lock mechanism", any time there is a problem with the P lock mechanism.

    But assuming the ECU announcing the problem is the thing that has to be replaced to fix the problem is sort of like shooting the messenger.

    The problem might well be the actual P lock mechanism. There is a bit of linkage inside the transmission, and an electric actuator mounted on the outside. The problem could be in wiring between the actuator and the ECU.

    It is possible for really low battery voltage to be implicated in a P lock problem (the ECU will say so, if so), but if reading lots of threads leads to thinking "everyone says it's the battery", that means we need some better threads. There's a way on PriusChat that certain ideas start getting repeated enough that they're just not easy to tamp down. If you get ten people who have P lock problems posting that they think it was the battery, and then thirty more posts (like this one!) get made where somebody read the other ten and repeats "I saw all the threads where everyone says it's the battery" even though they're only repeating other people's guesses, and then a hundred new posters read those threads and repeat them, voilà, PriusChat has created a new fact, true or not.

    The most direct way to proceed when the transmission ECU announces a "problem with P lock mechanism" is to plug in Techstream and ask it why it announced that, and it will tell you.
     
  3. VFerdman

    VFerdman Senior Member

    Joined:
    Jul 5, 2017
    1,164
    1,187
    3
    Location:
    Western Massachusetts
    Vehicle:
    2007 Prius
    Model:
    Three
    Shooting the messenger is the most popular way to react in humandom! That's how we humans do.

    As for weak battery creating P-lock error message, I can confirm that as a fact. I had that happening to me for a long time intermittently as the battery was on a verge of being too low for the ECU's liking. Using car's test mode for battery is not 100% reliable. 100% reliable way is to measure the voltage at the battery or at the fuse box under the hood with a good quality volt meter. If the problem has persisted for 5 years then I would not think it's the battery as the battery would die in less time than that if it was close enough to cause P-lock errors. I would still put a volt meter on the battery just to make sure. A five ear old battery may be getting ready to be replaced and is adding to the problem.

    I would also put the old ECU back in so as not to introduce more variables (the ECU you put in is a variable as you have no idea if it's good or not). Then go about troubleshooting. Read codes, look at things, get your hands dirty a bit and you'll probably solve the problem. Then report it here to add to the community wisdom. Who knows, maybe, just maybe something IS wrong with the P-lock!
     
  4. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    110,133
    50,050
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    i like how often people come here and say, 'i tested the 12v and it is fine" :rolleyes:
     
    VFerdman likes this.
  5. VFerdman

    VFerdman Senior Member

    Joined:
    Jul 5, 2017
    1,164
    1,187
    3
    Location:
    Western Massachusetts
    Vehicle:
    2007 Prius
    Model:
    Three
    Yes, that does happen a lot. And just as often it is followed by "I used a voltmeter and the battery is nearly dead" :)

    Toyota did put that "test" mode in there, so you can't put too much blame on the user. Not everyone knows what a volt meter is and how to use it.
     
  6. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    110,133
    50,050
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    i don't blame the o/p for using it. but reporting the results would be more helpful
     
    VFerdman likes this.
  7. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    24,906
    16,213
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    And again, the diagnostic code retrieved from the transmission ECU will flat-out tell you the problem was voltage if that's what the problem was, and the freeze frame you can pull with the trouble code will tell you what the voltage was at exactly that time. Or, it will tell you what other issue was detected instead.
     
    VFerdman likes this.
  8. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    110,133
    50,050
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    and yet, a dealer was not able to accomplish that
     
    VFerdman likes this.
  9. VFerdman

    VFerdman Senior Member

    Joined:
    Jul 5, 2017
    1,164
    1,187
    3
    Location:
    Western Massachusetts
    Vehicle:
    2007 Prius
    Model:
    Three
    The dealer wanted $2,500, not to fix a car.
     
    bisco likes this.
  10. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    110,133
    50,050
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    hey, it's a great gig if you can get it...
     
    VFerdman likes this.
  11. VFerdman

    VFerdman Senior Member

    Joined:
    Jul 5, 2017
    1,164
    1,187
    3
    Location:
    Western Massachusetts
    Vehicle:
    2007 Prius
    Model:
    Three
    As long as the customer understands what dealer's actual motivation is... Many customers don't. They think dealers WANT to fix their cars. Then they are surprised at getting ripped off and car still broken.
     
  12. VFerdman

    VFerdman Senior Member

    Joined:
    Jul 5, 2017
    1,164
    1,187
    3
    Location:
    Western Massachusetts
    Vehicle:
    2007 Prius
    Model:
    Three
    I realized that when I was a lad of 16 or so with my first (POS) car. I took it to a mechanic once and the second time I spent the money on a Craftsman socket set. Still have it, it has seen a lot of use. My cars rarely see the inside of a shop and practically never a dealer shop.
     
    Skibob likes this.
  13. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    110,133
    50,050
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    a dealer wanting to fix your car dislike a lawyer wanting your case to end
     
    VFerdman likes this.
  14. muddyjeff

    muddyjeff New Member

    Joined:
    Jul 5, 2019
    3
    0
    0
    Location:
    Pittston, Maine
    Vehicle:
    2008 Prius
    Model:
    Base
    Thanks for the wisdom everyone. I would not care to fix this but I now live in Maine and I can't pass the state inspection with that warning coming up on my information console and the red triangle illuminated. I was thinking of trying to pull the fuse, but I don't know if that fuse also controls other electronics that will make me fail as well.

    There are so many issues associated with this problem. Some folks can't put their car into gear, others won't start. For some, it happens when it's raining, which how mine began. This lead me to think that perhaps there is an opening in a wire that gets shorted out when it gets damp. I don't know.

    I've seen on this site as well as other places on the interweb that says this can also be caused by a faulty wire. Using a jumper wire from the "P Con Main" fuse to another seemed to do the trick. I posted the video below. What do you guys think about it? Last thing I want to do is fry the electronics in my car, then I'm toast. This is the only issue I've ever had with this car, going on 365,000 miles.

    Here's the video:
     
  15. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    110,133
    50,050
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    i don't like the mfd voltage meter because i don't know how much load is on it. does toyota give a spec for the reading?
     
  16. VFerdman

    VFerdman Senior Member

    Joined:
    Jul 5, 2017
    1,164
    1,187
    3
    Location:
    Western Massachusetts
    Vehicle:
    2007 Prius
    Model:
    Three
    11.8V is way too low and may be what is causing your P-lock message. Try a new battery or use a jumper cable and connect a known good battery with at least 12.4V on it when resting. Also, measuring the voltage of your 12V battery right after running the car (and charging it with 14.4V) is a bad test. You need to test it after it sits overnight with a meter, not MFD. If it's under 12.4V, there is a better than average chance it's one of the issues for your P-lock message. I am not saying there aren't more problems that cause this, but a battery under 12V is DEAD as far as Prius is concerned. Don't ask me how I know.
     
  17. muddyjeff

    muddyjeff New Member

    Joined:
    Jul 5, 2019
    3
    0
    0
    Location:
    Pittston, Maine
    Vehicle:
    2008 Prius
    Model:
    Base
    So here's a follow up. If you look at the video I posted earlier, it shows putting a jumper wire from the P Con Main fuse to the blue wire on the connector eliminated the Red Triangle of Death. I tried it and it worked! This was huge. I wouldn't be able to pass Maine state inspection with the light on.

    What do you think...will keeping the jumper wire connected eventually do damage? I don't want to fix the warning light but completely destroy the wiring harness and fuse box.

    As always, thank you for everyone's input.
     
  18. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    110,133
    50,050
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    poly not, but i'm just guessing
     
  19. Chuckx

    Chuckx New Member

    Joined:
    Dec 19, 2019
    4
    2
    0
    Location:
    Texas
    Vehicle:
    2005 Prius
    Model:
    III
     
  20. Chuckx

    Chuckx New Member

    Joined:
    Dec 19, 2019
    4
    2
    0
    Location:
    Texas
    Vehicle:
    2005 Prius
    Model:
    III
    My solution was passenger door handle malfunction l disconnected the good sized electrical plug behind the handle its self 2 screws whole door panel just pulls off a little force needed 5min fix

    Others possible causes listed...

    1. ToyotaPartDeal web site 33820 47020
    CABLE ASSY, TRANSMISSION CONTROL

    2. Transmission Moisture build up was causing a high voltage leak error code P to engage error, changed fluid.

    3. Transmission plug on park control motor being loose. remove plug and spray some contact cleaner. Then look for any likely spots for water getting in.

    4. Fuse number 34 is P CON MAIN fuse 7.5 amp Parking controlsystem, hybrid vehicle immobilizer system P Con Main fuse swap out worked triangle P lock error gone
     
    jeremybnz and SFO like this.