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Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
Satisfied Customers: 4909
Experience:  30+ Yrs of auto experience, Award Winning Svc. Manager; Just Answer Customer's Choice Award Winner
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My Prius won't start. I get the red triangle and the

Customer Question

My Prius won't start. I get the red triangle and the message:
"P lock malfunction when parking, park in flat place and apply parking brake securely"
I think I must have let the battery get a little low while I was working on something yesterday. I jumped the battery, but I cannot get the warning to clear. I have tried disconnecting and reattaching the battery.
I cannot check the battery via mfd, because it is broken. Voltmeter on the battery reads 12.8 volts. There is no reason for me to believe the battery is bad.
I have two questions:
1) Is it likely the battery is bad, even though it reads fine with the voltmeter?
2) If it's not the battery, how can I reset this computer so the car will run again?
I will pay if you can answer both questions correctly, and my car runs again.
Submitted: 2 years ago.
Category: Toyota
Customer: replied 2 years ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Customer: replied 2 years ago.
I don't need you to call me. I just wondered what would happen if i clicked on it.
Expert:  Toyota Service replied 2 years ago.

Hello. Welcome to Just Answer. Please allow me to assist you. A 'P lock malfunction' usually indicates a weak battery. Since you have a voltmeter, lets turn on the headlamps and then measure the voltage across the aux battery terminals. If it reads low, like under 11.5 volts, your Aux battery is too weak to power up the many computers inside the car. Additionally, jumping the 12 volt Aux battery rarely works iof the battery is weak. These sealed lead acid batteries need a 2 amp trickle charge to restore a discharged battery. Based on experienmce with the P lock malfunction indication, I would not be surprised to see that you need to replace the Aux battery in the rear hatch. .

If you have any questions, please feel free to reply.

Thanks for choosing Just Answer. It was a pleasure to assist you today. I trust my input to your request is satisfactory to you and meets your expectations. A positive rating would be greatly appreciated for my assistance on your inquiry.

Thanks in advance and thank you again for choosing Just Answer

Customer: replied 2 years ago.
Okay I checked the battery again. With everything off, it read 12.7
After turning on the headlights, it read 12.3
Turned off the headlights and it read 12.7 again.
Do you still think it's the battery?
Expert:  Toyota Service replied 2 years ago.

Sounds like it. The battery needs a bit more voltage. Do you have a 2 amp trickle charger?

Customer: replied 2 years ago.
I don't think so. Do you think that would work?
Customer: replied 2 years ago.
if I charge or replace the battery, is there some procedure required to clear the fault. The regular scanner doesn't read it, but it does try momentarily to clear it when I push "erase codes".
Expert:  Toyota Service replied 2 years ago.

Worth a try, a new battery is around 135 dollars. Procedure: disconnect the battery in the hatch and connect the charger set to 2 amps. Allow the battery to charge for a couple hours and restest your voltage. Make sure the battery terminals are clean and free of corrosion before attaching the charger This is exactly what I would be doing in my shop (if I did not have the fancy Toyota battery tester). If you have a Toyota dealer nearby, and alternate transportation, you could take the battery to them and have them test it.

Expert:  Toyota Service replied 2 years ago.

"regular' scanners are not compatible with the Prius product.

Expert:  Toyota Service replied 2 years ago.

I would charge the battery before anything else. The move forward from there. These batteries are very small, and do not have a very high amperage capacity, If one leaves the dome light on for a while, and the battery is older (we recommend replacement every 5 years), the battery may not recharge.

Customer: replied 2 years ago.
I don't agree that $135 is worth a try if it doesn't fix the problem.
My OBD scanner does work with this car. I have used it before.
When you say charge it, then retest the voltage, what should it be? I have read that it is supposed to be at least 12.6, and it is there now. How high would I want it to get if I put a charger on it?
Customer: replied 2 years ago.
Just one more time: Do you think the battery is likely to be bad if it is reading the proper voltage?
Expert:  Toyota Service replied 2 years ago.

I recommended charging the battery before expending money on a new battery. There is one other thing that can cause this code, and that is low converter coolant. Can you check the inverter coolant level under the hood?

Customer: replied 2 years ago.
I will. And I will take the battery to be tested at the dealer. How much do you think they'll charge me?
Expert:  Toyota Service replied 2 years ago.

Your scanner may 'work' on this car, but there are sub-codes that may be present that it is not reading.

Expert:  Toyota Service replied 2 years ago.

I do not charge anything to test a battery, if an hourly tech does the test. If the shop is all flat rate techs, expect to spend 1/2 hour of their posted labor rate.

Customer: replied 2 years ago.
Thanks. I'll let you know.
Expert:  Toyota Service replied 2 years ago.

You are very welcome. Hopefully your inverter coolant is full and the battery will accept the trickle change

Customer: replied 2 years ago.
I'll get back to you tomorrow.
Expert:  Toyota Service replied 2 years ago.

OK thanks

Customer: replied 2 years ago.
Okay, I found the problem. Remember at the beginning I said I was working on something inside the car. Well, the thing I was working on was replacing the blower motor for the air conditioning. I figured I must have let the battery run low, but I didn't want to run out and buy a new battery because mine was testing fine.This morning I thought maybe the work I was doing caused the problem somehow. In about two seconds I saw that the thing I unplugged under the blower was the called a transmission control. Hmm . . . exactly what the message on the screen says. I plugged it back in and all is fine.I'm not going to pay for this session. I appreciate you trying, but you couldn't help me this time. You just told me things I had already learned. When I come to, it's because I'm getting desperate and I need something more. I hope my experience helps you in the future -- remembering that little control module. Everything I read online said it was the battery, but this time it actually was the transmission -- because I unplugged it!Even though I don't feel that I should pay you, I don't want to give you a lesser rating. Is there any other way to avoid paying?
Expert:  Toyota Service replied 2 years ago.

Thanks for the update. In all honesty, I would not know that you disconnected the TCM. Our assistance here is based on everything being connected. In any case, there is no need to pay. It was a pleasure to assist you anyway. As long as you do NOT provide a rating, you will not be charged.

Customer: replied 2 years ago.
Thank you.
Expert:  Toyota Service replied 2 years ago.

You are very welcome. Have a great weekend