Charging issues when cold outside 07 Yaris. - Toyota Yaris Forums

Zombiesrock · 02-05-2026, 12:06 AM

Hi everyone, it has been a long time since I have posted anything on here. My good ol’ 07 HB has been running steady these many years. I bought him new in Dec 06 and he has 220,000 miles on him. The last 10 years of his life I have been working from home so he gets driven way low miles compared to the first half of his life.
So here is my dilemma. After 18 long years we had to replace the alternator. I got one from rock Auto in Jan of 2025. After we replaced the alternator in very cold weather, I noticed the battery light flickering. That had us take a good look at the battery (which was 7 years old…) and we noticed it was starting to swell, so we replaced it too. The flickering battery light went away. (The temp started increasing outside too).
Well, in late November of 2025 when we hit our first freeze in TN and my battery light started flickering again. This time however after driving for 15-20 minutes it actually stayed on, full glow, no longer flickering. I drove for another 10 minutes, ran into the store to complete my mission of shopping and When I started my car back up I expected the light to be on but it wasn’t. However on the way home after about 15 minutes it started flickering then came on again.
I got home, turned off and on the car again and tested the voltage. I was getting 13.5 or so. It was still cold outside all day that day.
I didn’t go anywhere for a couple of days and the temps started to go up outside, and my battery light quit acting up. So I just figured it’s an old car and is acting weird in the cold..
Well, then We moved from TN to TX on Dec 14. When a huge temp drop was hitting the country. It was 10 degrees outside when we started the long 16 hour drive.
My car battery light started flickering not long after getting on the road and about 30 mins in the drive the battery light came on fully - I drove with it for an hour at highway speeds…then all my warning lights came on and my car speed bogged down to about 40. You could barely see my headlights. Thankfully I was in a caravan of vehicles as part of the move so we were able to get my car to safety.
My husband said it went into limp mode because the battery is not getting proper charge probably. (We were at a gas station with no means of testing anything). While there I turned off my car, then tried starting it again and to our surprise it started…no battery or warning lights of any kind. So we let it run for about 15 minutes to see if anything would come on. No warning or flickering so we got back on the road. 15 minutes in it started again. Mind you it’s still 10 degrees outside and late at night at this point so I had my heater and lights, etc on. I was able to drive another hour like the first time before it went into limp mode again and we had to stop. We ended up trying again a third time to try to make it to family’s house in TX so we could tow my car the rest of the way to south TX the next day. So I drove without any accessories (including lights) to make it. (My husband drove his truck behind me and my sister in law was right in front. I did turn my lights on when cars drove past us (it was like 2:00am at this point).
Long story short we got it to San Antonio via a tow the rest of the way. My dad, who is a lifelong mechanic suspected it was the alternator (he was diagnosing over the phone since he lives states away). He has not heard great things about Rock Auto. So we returned it under warranty and got a replacement. we replaced it mid January(just a couple of weeks ago) . After replacing it all seemed well for a couple of days…but then it got below freezing in San Antonio and sure enough the dang light started flickering again. So, it only seems to have a charging issue when it’s cold and since it was a new alternator that couldn’t be the problem. I don’t think it was in the first place since the issue persists. It was 65 degrees here a couple of days ago and I drove hours around town with no issue. 4 days before that it was 31 and the light was flickering and staying on again. I’m assuming it has to be a wiring issue…but where do I start? I looked up replacement wiring harness, but it’s like the replacement was for all of the engine wiring, and was anywhere from
$500-800 which is probably the value of my car. I’d love to fix it but since it only acts up in cold I am lost at where to dig into this. Thanks for the help. Sorry for the book…

dkwilfert · 02-05-2026, 04:14 AM

The voltage regulator is built into the alternator, and on a quick search of the forum I found this post series that mirror your situation and concluded the aftermarket alternators often do not have good voltage regulators; emphasis on only using a genuine Toyota alternator.

https://www.yarisworld.com/forums/sh...tage+regulator

Zombiesrock · 02-05-2026, 07:39 PM

Thanks for the help. I had come across that thread too but was not certain if it was the same issue because it only happens in severe cold. It goes away when it’s warmer. However, I am still able to return my aftermarket alternator to Rock Auto for store credit. After doing research my best bet might be to use it towards a manufactured Denso OE one? Have any of you used that brand before on these?

02-05-2026, 12:06 AM	#1
Zombiesrock Drives: 2007 Bayou Blue (formerly) Join Date: Mar 2014 Location: TX, United States Posts: 27	Charging issues when cold outside 07 Yaris. Hi everyone, it has been a long time since I have posted anything on here. My good ol’ 07 HB has been running steady these many years. I bought him new in Dec 06 and he has 220,000 miles on him. The last 10 years of his life I have been working from home so he gets driven way low miles compared to the first half of his life. So here is my dilemma. After 18 long years we had to replace the alternator. I got one from rock Auto in Jan of 2025. After we replaced the alternator in very cold weather, I noticed the battery light flickering. That had us take a good look at the battery (which was 7 years old…) and we noticed it was starting to swell, so we replaced it too. The flickering battery light went away. (The temp started increasing outside too). Well, in late November of 2025 when we hit our first freeze in TN and my battery light started flickering again. This time however after driving for 15-20 minutes it actually stayed on, full glow, no longer flickering. I drove for another 10 minutes, ran into the store to complete my mission of shopping and When I started my car back up I expected the light to be on but it wasn’t. However on the way home after about 15 minutes it started flickering then came on again. I got home, turned off and on the car again and tested the voltage. I was getting 13.5 or so. It was still cold outside all day that day. I didn’t go anywhere for a couple of days and the temps started to go up outside, and my battery light quit acting up. So I just figured it’s an old car and is acting weird in the cold.. Well, then We moved from TN to TX on Dec 14. When a huge temp drop was hitting the country. It was 10 degrees outside when we started the long 16 hour drive. My car battery light started flickering not long after getting on the road and about 30 mins in the drive the battery light came on fully - I drove with it for an hour at highway speeds…then all my warning lights came on and my car speed bogged down to about 40. You could barely see my headlights. Thankfully I was in a caravan of vehicles as part of the move so we were able to get my car to safety. My husband said it went into limp mode because the battery is not getting proper charge probably. (We were at a gas station with no means of testing anything). While there I turned off my car, then tried starting it again and to our surprise it started…no battery or warning lights of any kind. So we let it run for about 15 minutes to see if anything would come on. No warning or flickering so we got back on the road. 15 minutes in it started again. Mind you it’s still 10 degrees outside and late at night at this point so I had my heater and lights, etc on. I was able to drive another hour like the first time before it went into limp mode again and we had to stop. We ended up trying again a third time to try to make it to family’s house in TX so we could tow my car the rest of the way to south TX the next day. So I drove without any accessories (including lights) to make it. (My husband drove his truck behind me and my sister in law was right in front. I did turn my lights on when cars drove past us (it was like 2:00am at this point). Long story short we got it to San Antonio via a tow the rest of the way. My dad, who is a lifelong mechanic suspected it was the alternator (he was diagnosing over the phone since he lives states away). He has not heard great things about Rock Auto. So we returned it under warranty and got a replacement. we replaced it mid January(just a couple of weeks ago) . After replacing it all seemed well for a couple of days…but then it got below freezing in San Antonio and sure enough the dang light started flickering again. So, it only seems to have a charging issue when it’s cold and since it was a new alternator that couldn’t be the problem. I don’t think it was in the first place since the issue persists. It was 65 degrees here a couple of days ago and I drove hours around town with no issue. 4 days before that it was 31 and the light was flickering and staying on again. I’m assuming it has to be a wiring issue…but where do I start? I looked up replacement wiring harness, but it’s like the replacement was for all of the engine wiring, and was anywhere from $500-800 which is probably the value of my car. I’d love to fix it but since it only acts up in cold I am lost at where to dig into this. Thanks for the help. Sorry for the book… Last edited by Zombiesrock; 02-05-2026 at 12:12 AM. Reason: Typo

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
NEWS: TOYOTA REVEALS ALL-NEW YARIS SEDAN AT 2006 LOS ANGELES AUTO SHOW	VitzBoy	General Yaris / Vitz Discussion	7	09-20-2023 07:50 AM
Yaris A/c blows cold air and then after a while it blows hot and cold again.	Pong1975	DIY / Maintenance / Service	4	10-22-2016 03:27 AM
2012 Yaris Sedan. Dash lights, charging issues	PhoenixDriver	DIY / Maintenance / Service	1	07-04-2016 07:04 PM
2007 Yaris Pricing Info !	YarisBueller	New YARIS Purchase Forum	104	06-24-2009 04:54 PM
Yaris perofrmance issues	aucorium	DIY / Maintenance / Service	13	01-31-2007 02:30 PM

02-05-2026, 04:14 AM	#2
dkwilfert Drives: 2008 Yaris 2-Door (White) Join Date: Jan 2014 Location: Knoxville, TN Posts: 18	The voltage regulator is built into the alternator, and on a quick search of the forum I found this post series that mirror your situation and concluded the aftermarket alternators often do not have good voltage regulators; emphasis on only using a genuine Toyota alternator. https://www.yarisworld.com/forums/sh...tage+regulator

02-05-2026, 07:39 PM	#3
Zombiesrock Drives: 2007 Bayou Blue (formerly) Join Date: Mar 2014 Location: TX, United States Posts: 27	Thanks for the help. I had come across that thread too but was not certain if it was the same issue because it only happens in severe cold. It goes away when it’s warmer. However, I am still able to return my aftermarket alternator to Rock Auto for store credit. After doing research my best bet might be to use it towards a manufactured Denso OE one? Have any of you used that brand before on these?