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2021 Sienna XLE
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I wish I could! As a carpenter I feel uniquely unqualified to figure this out. The dealer has however thrown their hands up. They have zero ideas other than “you keep leaving your lights on”. They are saying it’s our issue and we have to take responsibility.
It is pretty hard to leave things on that will drain the battery. Put the headlights in AUTO mode. The car will then control them and shut them off automatically. The interior lights are automatically shut off after a period of time (about 30 minutes) even if you leave the doors open. This is not enough to run the battery down so it won't start. The 12 volt outlets and the USB outlets are not powered when the car is off. You either have a bad battery (people have had bad batteries replaced) or there is something that is draining the battery. As mentioned above, there is a TSB regarding possible battery rundown after the battery was disconnected and reconnected. I am not sure whether this applies to 2022 models or not.
 

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2021 Sienna XLE
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We have about 8000 miles on it and all the sudden it has been not starting.. I go out open the sliding doors with the button; so they auto open just fine. Put my kids in. Go to close the doors; by the button and it won’t close. Go to start it lights and sounds but won’t start. The dealer replaced the battery earlier this week then it happened again. They kept it this weekend and I am going to go back and fingers crossed they find something but I’m afraid they won’t. We have been through making sure no lights are left on and nothing plugged in. We have also stopped keeping the key fob inside the van because the dealer believed that could cause an issue. I disagree with that though because we leave it in the car because we have a garage and have done that ever since we got it and never had an issue until recently.
There is a DCM software update that applies to vehicles made approximately before January 2021. If your vehicle was built in 2020, the DCM can cause the battery to run down if it loses the cellular signal. It then fails to re-aquire the signal and keeps trying. running the battery down.
 

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2021 Sienna XLE
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744 Posts
You might try turning off the smart key system for a few days. Our Gen 2 Prius manual said to turn off the smart key system if leaving the car inactive for a period of time as it would drain the 12v battery. Especially if the key fob was near the vehicle where the two could communicate with each other. I'm not sure if the sienna has a smart key system on/off switch like the early Prius' did.
The key fob can be put to sleep by holding the lock button and pressing unlock twice. The fob will not communicate with the car again until any button has been pressed on the fob.
 

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2021 Sienna XLE
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I'm in Canada. 2022 XSE AWD. Battery has drained 11 times in the 7 weeks I have owned the van.
It could be worse, but i installed the COMFORT+ package that comes with a battery charger. Takes about 15 minutes to charge the battery enough to start the van. It's a good idea to get that type of package in Canada, but honestly I never thought i would need it unless it hit -20C. I need it everyday to get the battery enuf juice to get out of the driveway

I was at the dealer today. They tested the 12V battery and say it's perfectly fine. Their opinion is the DCM is failing to communicate properly to Toyota's Satellite and it's causing just enough of a drain at 300 mA to drain the battery.
Dealer mechanic pulled the fuse to disable the DCM, and we are going to go 2 weeks and see what happens.
They don't believe it's a wire harness issue,and there are NO fault codes getting recorded by the van

The DCM draining the battery was a problem in 2020 and 2021 RAV4 and Camry. The big problem here is there is NO SOFTWARE updates for 2022. And I'm in Canada and we might get our own software update which could take longer.

I don't like the thought of the DCM being disable. Toyotas are highly stolen cars in Canada esp Highlanders, Tacomas and Siennas. the DCM allows Toyota to track stolen vehicles. I bought an Apple airtag for it.

I'll try to update, but for now dealer told me to keep driving and parking as normal and begin to track battery drains. Cross our fingers it's this DCM celluar issue!
In theory, the DCM battery drain issue was fixed by a DCM software update early in production of the 2021 models. The 2022 should have that software update installed as it has been installed at the factory since around January 2021. The original problem was related to losing the cellular signal and not being able to reacquire the signal. When the DCM is trying to find a cell signal, it uses more power.
 

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2021 Sienna XLE
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744 Posts
I'm having similar issues. Picked up a Limited on Jan 24th, a couple days later I got a notification on the Toyota Connected app that a "window was down". Went outside to check the car, no windows down, went back inside. Next morning the battery was dead. Second time it happened I used the app to lock the van when it told me it was unlocked (i had run an errand and didn't lock it when I got home), the next morning it was dead. Took it in today to the dealer, they checked the battery and claimed it was dying due to short trips plus the extreme cold. Not feeling like that is the correct answer, given that the only times it happened the Toyota Connected app was involved. I feel like it was something to do with the DCM.
I doubt it is due to short trips. In a non-hybrid that tends to be an issue, since it requires a large amount of power to start the car. It takes the alternator some time to replenish the energy consumed by the starter. In the hybrid, the battery just powers the computers that run the car. The engine is started using power from the traction battery. So there is no large consumption of energy when the car is started. In addition, the Sienna battery is smaller requiring less time to get to a full charge. So far, the battery drains have been traced to the DCM (2021 models primarily) and the kick sensors (2022 models).
 

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2021 Sienna XLE
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May be the number of users? Last winter was the first one for this Gen. I suppose a lot fewer users last winter didn't cause all possible issues to bubble up until now?

FWIW, sitting in the car with lights and music on for about 15 minutes is enough to trigger the Low battery symptoms. I had it happen to us this week when kids got to it 15 minutes before I did. They got the ACC on for music. When I tried to get it going, I got the parking brake message. Luckily, cycling it off and on got me going again. Temperature was in 30s.
My Sienna was at the dealer yesterday. I happened to be at the car to discuss something with the tech. I noticed that they had a NOCO jump starter attached under the hood. I guess they have found that it is easy to run down the hybrid batteries while working on the vehicles, so they keep the battery charged with the NOCO. I did see that the battery voltage was running at 12.8 volts or so all the way home, which indicates the battery had a full charge. When the battery needs to be charged, the voltage runs about 14.4.
 

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2021 Sienna XLE
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Just curious, why would the voltage be higher if it neeeds to be charged?
As with many current cars, the charging voltage varies with the charge level of the battery. Once the battery is charged, the charging voltage is lowered to prolong the life of the battery (not overcharging it) and to marginally increase fuel mileage (CAFE targets are very important to manufacturers and every little bit helps.) Essentially, 14.4 volts is the charging voltage and 12.8 volts is the maintenance voltage.
 

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Just wondering, anyone experience a similar situation with the 2021 Sienna? I have the 2021 model. I got the vehicle back in July 2021. But since then I have jump started my car at least 10 times since then due to battery not enough charge to start the vehicle.

I have gone back to the dealer to check but they say battery has no issues. They say I may of not drive the car enough. Which may be true. I only get to drive it 2-3 short trips a week now adays. But my driving habit is the same with my previous vehicle(non-hybrid). And I never had a problem. So I am wonder if my car has the same kick sensor issue like the 2022 models.
Do you park in an area with little to no cellular service, particularly with the carrier that Toyota uses. (in the US, the carrier is AT&T, not sure if it is the same in Canada). The vehicle can go into a mode where it is searching for cell service. This uses more power than when it has found a tower with service.
 
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