Problem with "P" Lock Mechanism

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.

 

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!

 

i like how often people come here and say, 'i tested the 12v and it is fine"

 

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.

 

i don't blame the o/p for using it. but reporting the results would be more helpful

 

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.

 

and yet, a dealer was not able to accomplish that

 

The dealer wanted $2,500, not to fix a car.

 

hey, it's a great gig if you can get it...

 

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.

 

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.

 

a dealer wanting to fix your car dislike a lawyer wanting your case to end

 

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?

 

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.

 

poly not, but i'm just guessing

 

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