There is a problem with the transmission p lock mechanism

Concerning my 2005 Prius. Mileage 147,500. Replaced the big battery twice, both from the Houston battery firm. Reasonable price, decent service lift, thought not great.

Recently replaced the 12V battery for 2nd time. Used the Optima battery both times. The last time, just a month ago, I bought from Amazon (free Prime delivery). Problem: Amazon has the wrong part number for use in the 2005. Worked out OK though.

I don't get great gas mileage. Never have. Best when new was about 42-45. Lately it runs about 30-35. Most of my trips are only about 2.5 miles each way.

Current problem is disabling. It started about two weeks ago when I tried to start I got the big red triangle and the message:
"The Transmission [P] lock mechanism is abnormal. Park your car at a flat place and apply parking brake completely."

At the time the indicator shows P and can't be put into reverse or forward. Therefore, can't go anywhere

Both times I was able to turn the switch on and off several times and finally got it to go into gear and go. But by this time I was afraid to take it anywhere.

Tried to get error codes with my Torque Lite app and the OBDII. No luck for some reason.

Any ideas. Right now I'm afraid to take it anywhere. Thanks in advance

Test the 12 V battery.....thoroughly.....and the main connections to it.
The Optima is known for early failures.

If you have a battery charger, connecting it for a good long charge might get you going.

Did you check the charging voltage with the car "running" after you changed the 12 V battery last time ?

Test the 12 V battery.....thoroughly.....and the main connections to it.
The Optima is known for early failures.

If you have a battery charger, connecting it for a good long charge might get you going.

Did you check the charging voltage with the car "running" after you changed the 12 V battery last time ?

I connected the charger overnight. When first connected it showed 70% charged. Charged to 100%. No help.
Checked the charging voltage with the car running. 14+ volts.
Tried again today to start it. Went into gear 1 time in about 30 tries, even though the Red Triangle didn't go away. But soon reverted to the "Park" problem and wouldn't go into gear

It appears that you missed the second part of my recommendation.
Before you haul it off to the shop, you need to check those main connections.
That is both ends of both main battery cables.
The frame end of the negative cable is often a problem.

And by "check", I mean loosen and re-tighten each one and check for corrosion in the process.

I did a Google search on the P-Lock error message and found a number of references and YouTube videos.

Several of these videos explain what many have done to fix the problem. The URL I selected to follow is:

That video is made to fix a 2007 Prius but my 2005 has the same fuse block layout.

Basically the fix is to connect a wire from the left side of the top 7.5 A fuse, labelled "P Con Main" to the fourth pin from the left in the upper row on the topmost, upper left connector.

Supposedly the original connection between those two points has failed and the jumper wire we add fixes the problem.

It worked. But I wish I had a Prius schematic so that I could verify what this fix accomplishes. I haven't found the explanation yet.

I have not ignored your suggestion to thoroughly check the Optima battery connections and I will do that soon now that I have the car running again.

Thanks very much for your help.

I wouldn't rely on that "fix" without knowing exactly what it does.
You might be disabling a critical feature of the braking system.
There are a LOT of people who post things on the net that are illegal and dangerous.......sometimes just for the "fun" of it.

Do you know where I can get free access to a 2005 schematic? Do you have it Easy Rider?

Do you know where I can get free access to a 2005 schematic? Do you have it Easy Rider?

No, sorry I don't.