Red Traingle with a message that there is a problem with the transmission"P" lock mechanism

That symptom almost always means that you have a discharged 12v battery. Check the 12v battery voltage either with the car off or in ACC mode (Press power without pressing the brake). You can either use a voltmeter ($25 at radio shack) or put your Prius in maintenance mode (see: Checking 12v Battery Health - Hybrid Car Forums ). You probably need a new 12v battery.

JeffD

 

Replace the 12V battery now. That will take care of the strange warning msg.

 

I have the same P Lock message. I have to ask Why would I replace my battery. I checked it and with the car off it has 12.74 v. Tha seems like a good battery to me. What am I missing?

 

And I am having this issue with my 2nd Prius, a 2007.

 

is it the original battery? did you check it at the terminals, before starting the car in the morning?

 

I had the same issue last week. I bought my 2007 on Tuesday and on Thursday I got the red triangle and everything shutdown. I got the "P-lock in the transmission does not work" message and instructions to get on a level surface and apply the brakes. Hard to do when I can't put the thing in reverse or drive. Eventually after a series of turning things off and on, applying parking breaks and pressing various buttons, I go it into gear and drove home, red triangle still lit up. I read some Prius forums and followed the direction to pull the 7.5 amp fuse then put it back, red triangle remained. I checked the battery and it was at 12.74v (car not running) so I knew I did not have a battery problem). Then I removed the negative cable from the battery, cleaned up the cable connections, the terminal and the spot where the cable connects to the body (this had a lot of paint on it that I cleaned off. I sanded it down to the metal. I put the negative cable back on. I disconnected the positive cable from the battery and cleaned that connection up then reinstalled it. I started the car. The red triangle was gone and it has been running fine since (knock on wood).

 

did you notice any water in the battery area?

 

I have a 2006 Prius and I got the dreaded P-lock mechanism warning but I was able to put the car in neutral and then park and then start it up. I waited a day and went into diagnostic mode and saw that the battery was weak so I brought it into a Toyota dealership and they replaced the battery after checking see it that the charging system was working well and that the battery (5 years old) was weak. I then drove home and the next day when my wife went to start the car I got the dreaded triangle and P-lock warning again. One thing the dealership did find was evidence of rodent activity under the hood. Can it be that the rodents chewed through some wires that are causing the error message to reappear despite having a brand new battery?

 

That's certainly a possibility. You didn't mention anyone checking the trouble codes/freeze frame data from the transmission control ECU before trying the battery-replacement route. If the diagnostic information points to possible wiring damage, that would be more evidence toward the rodent idea. In any case, getting the data would be the next step ... it will point somewhere.

Out of curiosity, what voltage did you see in diagnostic mode at the time you concluded the battery was weak?

-Chap