Intermittent trouble starting

To rule out it is a weak battery or not (without buying a new battery), just load test the battery. Simply measuring the voltage isn't enough.
My original battery lasted about 9 years. And when it went out, it was still showing 12.5 standing voltage. But when I turned the headlights on (without turning the car on), the voltage took a dive. Then I knew it was time to replace the 12v battery.

You may also go to any local auto parts store and most will test your battery for free.

 

I am also having this intermittent problem with my 2012 wagon. Sometimes it is completely dead, then 5 minutes later it will come on or it may show a red padlock - I changed my key fob battery but that didn't really help. Sometimes the cabin lights are dim, sometimes the whole dash is dark, sometimes the start switch goes to red, sometimes it says KEY; I go inside to borrow a car and when I come back my car suddenly lights up BY ITSELF, no one in the car and all the dash is on and the radio. Then it usually starts. It has always started after 5 -6 tries. I went to Interstate Battery and they tested it, then had me turn my headlights on, and off. They said I had 92% health and 96% charge.

I bought the car used 2 1/2 years ago. I don't know if it's the original battery - there is no date on it. (which makes me think maybe it is original). I called my regular mechanic and described the problem and he suggested an electrical guy. He wanted nothing to do with it!

Does the hybrid battery charge the 12V? How does it go from "dead" to dim to fine? It happens much more if it sits 4 hours and if the weather is colder - but in N central Florida, that is maybe 35 degrees. It seems like it may be the battery but it's the weirdest battery thing I've ever seen if that's the case. Also it started on a cold night and is mostly fine during the day except when the temperature goes to 32 and it has been sitting.

How does the battery need to be tested?

 

Read the reply directly above yours and check the last sentence in the reply.

 

I have already had it tested at a battery supplier - all they do is automotive batteries. They said it was fine. But I'll try testing it somewhere else. Reading different threads it seems others get a good test, but when they replace the battery the problem goes away.

 

I'm having tgus same issue too, except it happens everytime i start. 2014 prius. When i first start, the dash turns on, the ac turns on, nothing else.. 5 minutes after starting, it will eventually engage every thi g else and the car drives just normal. I've already replaced the 12v once, still under warranty i might replace it again. I'm hoping someone else finds a solution.

 

might be cheaper to test it

 

2013 Prius got it in February. Has had this same issue 3x over the last month. It was in at Toyota today and they say it needs new 12v battery. I do not find any information on 12v batteries where they provide no power (maybe 1 dash light and the inverter fan) but then start just fine 5mins later. Dead batteries die and need to be recharged. I have uploaded the reading from my battery. It could use replacing at 107cca with a stated cranking of 350cca. My work is that this acts more like a wiring issue and it could kill a new battery.
Toyota has no clue... this is clearly an issue on multiple cars. Hi do we get them to find/fix the actual problem?

 

So, I showed at an auto parts store I needed a battery after getting jumped by a tow truck for the second time. It was the 12v, though a battery store told me it was “fine”. So, an easy fix. I can’t complain about a battery that lasted over 7 years, even though it did the strangest stuff I’ve ever seen. It was like the car had a ghost for about a month.

 

2016 Prius C Tech rebuild. I have started having this problem this summer 2021 on about 5 of 50 starts. Fob(s) fine, the amount the break depressed doesn't change out come, lights interior and exterior all at normal levels. During a normal successful start up the dash all lights up and lights go out as it boots. During a failed attempt it almost sounds like a relay isn't connected and hangs the system often at the "pre-collision not available". Windows clean, parked indoors. Not consistent with long or short drives / or time between start ups.

Planning a trip to the dealer. I will return with results.

 

1 Week after the dealer replaced the AUX battery, I have not had a repeat of the symptoms. May have paid more than I needed but they were confident they had seen and fixed these issues with success.

 

Thank you for posting. I am having the exact same problem with my 2011 Prius. I replaced the 12V battery about six months ago unrelated to this issue. About two months ago this problem started. It seems like it is getting worse. Did you ever figure out any resolution?

 

could something be draining your new 12 volt?

 

I cannot think of anything draining the battery. Even if something did drain the battery, why would it eventually start after multiple attempts of cycling the power on and off? Why would it work perfectly fine sometimes and take multiple attempts the next. Rather than the battery it seems like something is stuck sort of like a stuck solenoid on a conventional vehicle starter. Maybe after a few attempts it finally works? I know very little about how the Prius batteries work and interact. I have put over 250K on this car in the last decade with virtually zero issues until now.

 

I had the same exact problem. I searched this site and others for a solution. I am happy to report I figured out the problem. The negative battery cable was loose where it attached to the car chasse. After tightening it up, the car has started perfectly.

 

UPDATE: I am thrilled that I finally solved this problem. The negative battery cable was loose where it attached to the car chasse. After tightening it up, the car has started perfectly.

 

I had the same issue and it turned out to be the fact that I had my Sienna smart key with me. Whenever it’s with me the Prius acts up. Won’t start. Doors are finicky about unlocking. Leave it at home and no problems at all.

 

I would try making sure you don’t have another car key with you. My Prius won’t act right if my Sienna key is with me. Won’t start. Won’t lock and unlock right. Everything works eventually but it’s a huge waste of time and a bummer to boot.

 

I know how to definitively solve the starting problem but I don't know why it happens.

I own a 2006 Prius and nearly every time I turn off the car, it won't completely start. I connected an OBDII scanner to it permanently and when it doesn't start, I erase all it's error codes. I turn off the car and then turn it on again and it works.

I can't loan the car to anyone because I know they will forget how to get it started when it acts up.

 

what if you repaired the car?

 

I have been having this problem for the last 2 months with my 2014 Prius IV. Exactly the same behavior as the original poster experienced. 2 mechanics and a dealer reboot later, no one knows what's up but it's getting much worse! Aux battery seems strong - I think it's less than 2 years old. I'll check the neg connection but I think mechanic #1 was all over the potential aux battery possibilities.