Please help, Prius sometimes won't start on first try

lizardqueen · May 21, 2022

Maybe y'all can help me with some insight as to what is wrong with my car.
It is a 2011 with 185k miles.
within the last few weeks i noticed that using the key fob won't unlock the trunk sometimes, but pressing the unlock button on the door will unlock it.
since then, I occasionally have to press the start button twice to get my car to turn on, this is becoming more frequent.
then last night I went to turn my car on and it would not turn on even after pressing the start button a bunch of times. this is when i started to be really worried. the trunk wouldn't open also, (i know that it needs power to open). eventually i got it to start , but when i went to turn on the headlights, the car turned off. a couple minutes after that, I tried to start it again and it worked fine and I was able to drive home.
today i tried to do some troubleshooting. I tried locking and unlocking the car using the key fob. it would lock and unlock the doors just fine but not the trunk. both my key fob that i use everyday and my spare which i know has a full battery behaved the same, so i think i can rule out the key fob being the problem.
then i took my multimeter and measured the auxiliary battery. it measured a 12.5v so i think that is fine.

i know that the hybrid battery is only supposed to last 150k miles. but i also read on some websites that it is supposed to last the lifetime of the car, which i know toyotas can last twice that. i know that my battery isn't holding charge like it used to , but i'd like to put off replacing it for as long as i can.

are there more options as to what might be wrong with it, or is it just time to go ahead and replace the big battery? I don't want to take it to a shop who is just going to tell me to replace it if theres a chance that there is something else going on.

thank you

bettergolf · May 21, 2022

Test the 12v battery....the hybrid battery doesn't usually just "go bad" without some kind of warning lights or codes. The 12v battery can cause all kinds of weird problems that don't even make sense.

ASRDogman · May 21, 2022

12.5 is getting low, for the Prius. How old is it? 5+ years, and it's about time to replace it.
How often, and how long do you drive? You may not be driving it enough to keep the battery charged.
You could trying putting a 4amp or less charger on it over night, if you don't drive much.

lizardqueen said: ↑

Maybe y'all can help me with some insight as to what is wrong with my car.
It is a 2011 with 185k miles.
within the last few weeks i noticed that using the key fob won't unlock the trunk sometimes, but pressing the unlock button on the door will unlock it.
since then, I occasionally have to press the start button twice to get my car to turn on, this is becoming more frequent.
then last night I went to turn my car on and it would not turn on even after pressing the start button a bunch of times. this is when i started to be really worried. the trunk wouldn't open also, (i know that it needs power to open). eventually i got it to start , but when i went to turn on the headlights, the car turned off. a couple minutes after that, I tried to start it again and it worked fine and I was able to drive home.
today i tried to do some troubleshooting. I tried locking and unlocking the car using the key fob. it would lock and unlock the doors just fine but not the trunk. both my key fob that i use everyday and my spare which i know has a full battery behaved the same, so i think i can rule out the key fob being the problem.
then i took my multimeter and measured the auxiliary battery. it measured a 12.5v so i think that is fine.

i know that the hybrid battery is only supposed to last 150k miles. but i also read on some websites that it is supposed to last the lifetime of the car, which i know toyotas can last twice that. i know that my battery isn't holding charge like it used to , but i'd like to put off replacing it for as long as i can.

are there more options as to what might be wrong with it, or is it just time to go ahead and replace the big battery? I don't want to take it to a shop who is just going to tell me to replace it if theres a chance that there is something else going on.

thank you
Click to expand...

prius16 · May 21, 2022

It sounds like your 12volt battery.
A 12volt battery lasts ~3-5 years. Just because some people have very old 12volt batteries, that does not mean that 12volt batteries last a long time.
It means: That some people get lucky.
Yea, spending money on replacing a 12volt battery isn't fun. Especially with the prices of batteries today. (This month, I spent $80 for a Lawn Tractor battery - ugh!.)

However, all automotive 12volt batteries are wear items (like tires), and should be replaced after ~3-5 years.
You can drive on worn tires, with little tread. That doesn't mean it's a good idea.
The same is true for an older 12volt battery.

Expect your Toyota Prius hybrid battery to last ~200K to ~300K miles. So, ~~250K miles typical?
There are many factors.
You're in Tennessee. Imho, you're in a Very Good location for life expectancy of Hybrid batteries.
It's not always warm/hot. And, your "cold" months, are good for Hybrid batteries (not too cold ).

Good Luck!

rjparker · May 21, 2022

Have the 12v battery load tested at a shop or auto supply. Blindly changing it could work but its just as likely to be $250 that does not fix it.

bisco · May 21, 2022

lizardqueen said: ↑

Maybe y'all can help me with some insight as to what is wrong with my car.
It is a 2011 with 185k miles.
within the last few weeks i noticed that using the key fob won't unlock the trunk sometimes, but pressing the unlock button on the door will unlock it.
since then, I occasionally have to press the start button twice to get my car to turn on, this is becoming more frequent.
then last night I went to turn my car on and it would not turn on even after pressing the start button a bunch of times. this is when i started to be really worried. the trunk wouldn't open also, (i know that it needs power to open). eventually i got it to start , but when i went to turn on the headlights, the car turned off. a couple minutes after that, I tried to start it again and it worked fine and I was able to drive home.
today i tried to do some troubleshooting. I tried locking and unlocking the car using the key fob. it would lock and unlock the doors just fine but not the trunk. both my key fob that i use everyday and my spare which i know has a full battery behaved the same, so i think i can rule out the key fob being the problem.
then i took my multimeter and measured the auxiliary battery. it measured a 12.5v so i think that is fine.

i know that the hybrid battery is only supposed to last 150k miles. but i also read on some websites that it is supposed to last the lifetime of the car, which i know toyotas can last twice that. i know that my battery isn't holding charge like it used to , but i'd like to put off replacing it for as long as i can.

are there more options as to what might be wrong with it, or is it just time to go ahead and replace the big battery? I don't want to take it to a shop who is just going to tell me to replace it if theres a chance that there is something else going on.

thank you
Click to expand...

change the fob battery

how old is the 12 volt?

TMR-JWAP · May 21, 2022

Your symptoms are indicative of a failing 12v battery or a loose connection in the 12v battery circuit.

lizardqueen · May 22, 2022

prius16 said: ↑

It sounds like your 12volt battery.
A 12volt battery lasts ~3-5 years. Just because some people have very old 12volt batteries, that does not mean that 12volt batteries last a long time.
It means: That some people get lucky.
Yea, spending money on replacing a 12volt battery isn't fun. Especially with the prices of batteries today. (This month, I spent $80 for a Lawn Tractor battery - ugh!.)

However, all automotive 12volt batteries are wear items (like tires), and should be replaced after ~3-5 years.
You can drive on worn tires, with little tread. That doesn't mean it's a good idea.
The same is true for an older 12volt battery.

Expect your Toyota Prius hybrid battery to last ~200K to ~300K miles. So, ~~250K miles typical?
There are many factors.
You're in Tennessee. Imho, you're in a Very Good location for life expectancy of Hybrid batteries.
It's not always warm/hot. And, your "cold" months, are good for Hybrid batteries (not too cold ).

Good Luck!
Click to expand...

thank you! it ended up being just a lose connection on the 12v.... crazy how i thought i was in for a 4000$ repair and all i ended up having to do was tighten a screw lol... 200k to 300k?! thats awesome i did not know that, when i google how long theyre supposed to last i get so many different answers

TMR-JWAP · May 22, 2022

Grit · May 22, 2022

lizardqueen said: ↑

...the last few weeks i noticed that using the key fob won't unlock the trunk sometimes...it would lock and unlock the doors just fine but not the trunk.
Click to expand...

Which button on the remote do you press to open the trunk?

Please help, Prius sometimes won't start on first try

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Please help, Prius sometimes won't start on first try

lizardqueen New Member

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rjparker Tu Humilde Sirviente

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TMR-JWAP Senior Member

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