Parasitic battery drain?

You really shouldn't believe everything you read, and certainly not take it to extremes like that. The idea of "only plugging in to charge for an hour or two" rather than just leave it overnight is daft.

And, unsurprisingly, it didn't help.

As far as I can see, nobody has ever reported a failure that that seems to be due to it being plugged in a long time. This only comes from a sentence in the manual which points out that leaving it plugged in doesn't help maintain charge, so it's not a good idea to just leave it plugged it.

But obviously it's designed to be plugged in overnight. That's the whole usage model of the car. You only need to start thinking about not leaving it plugged in if you're planning days of no use. Making the effort to not leave it plugged in overnight makes about as much sense as disconnecting the 12V battery overnight or overinflating the tyres overnight. Both of those are similar preventative measures you'd want to think about for longer term non-use, but not required for normal operation.

The TSB here does seem to describe what people have been reporting which is an unexpected sudden rapid short term drain - clearly not intended, and random enough to be a software glitch, and NOT the expected long-term behaviour described in the manual.

And given that it's unintended behaviour, it's hard to say what exactly could trigger the "no sleep" condition. I doubt the TSB description totally captures it. It could be that stopping charging before complete could trigger it - charging ECU stays active after you pull the plug.

(And obviously this isn't something that the charger always does, or it would have been spotted - I'm guessing that it's dependent on some sort of hardware tolerance issue, so you need a combination of a car where some signals are a bit out of what was expected, and the ECU code that doesn't cope. The TSB says to only apply it if the problem's been seen - it could be they view it as a hardware error and the software update is to make it cope with the hardware error, rather than viewing it as a software error).

 

I'm thinking of getting a coulomb counter/data logger to put on the 12V battery. This will require a current shunt capable of handling whatever the max amperage is. Does anyone happen to know the main fuse rating for the 12V battery? I scanned through the list posted here, but I'm either blind or it's labeled in a way that's not obvious.

 

15,000 miles with no issues at all with the battery even after letting it sit for a few days without driving or leaving it plugged in for up to 24 hours at a time (sometimes forget it's plugged in).

You have a bad battery. My suggestion is aftering reading thru all the issues other have had with their 12V batteries, quit accepting the dealer's explanation about the health of your battery (since they don't really know) and have them install a new battery.

 

Thanks. They installed a new battery May 20. Three weeks later, we had the same problem—dead battery overnight (not charging). On Monday they applied the TSB for the charging ECU. We’re monitoring the battery. So far so good, even though it didn’t happen after leaving the AC charger plugged in.

 

Yeah, plenty of people have had no problem, including myself, and plenty of people who have had the problem have had it reoccur after replacing the battery - I don't think the "bad battery" hypothesis has had a lot of success. It could make sense, but now that Toyota have issued that TSB, I think the charging ECU update is a better bet. (Although you might still want to replace the battery anyway if it's been flattened.)

 

My story :
Prius 3 2010 , bought in 2016 , after a long drive with family , I parked the machine and shut off the system, open all doors and hatch to discharge the people and luggage like 10 minutes it takes ~.
I noticed that didnt parked well alligned and close all doors and hatch, and try to get in Ready Mode, it keep tell me that the machine is not in P mode and to put in P mode, but on dashboard it was in P , but it keep tell to put.I call a friend with experience with Prius and told me to locked the machine and goes away and comeback after 30-60 minutes, and he guarantee that I can get in Ready Mode.He was right...and told me that 12v battery is old and start to loose power, also he suggest to replace all the bulbs with LEDS to avoid in future this problem.
I replaced the old battery ( original Toyota ) with simple and cheap Varta 40Ah type, and the bulbs and there are ~8 years from that moment.
Now , is started to manifest again, but in other way:
In noticed that it flashing lamps on dashboard and beep like crazy and wont start the system.After 4-5 tries suddenly it start.
I measured the voltage in Ready Mode ~14.7V because the battery was depleted, later found.
I drove a few km to job , after 8hr same issue problems at starting, measure the battery and found 7.9V-8V....
hmmm...looks like a dead battery...I unpluged the connector and measure again, It jump to 10V,.I decide to let till next day to see how much the battery is affected.
Next day i measured like ~10.8V , were enough to get in Ready mode and decide to replace the baterry a new one since 8 years could be a factor.
So, before replacing the battery I decide to check more things since I found that there some topic related with drain battery overnight.
I put a clamp ammeter on positive conector of old battery and read 1.3-1.5 A consumption with machine shut off, doors opened , I open the doors , check the switch by pressing, unplug all the LEDS, the OBD, the charger from 12V port, anything that could drain the battery.But the reading remain on same values 1.3-1.5 A.
I replace the battery, let the machine do the routine for 5 minutes , close myself in car,, all doors closed , the reading was same 1.3-1.5 Amps, I push the lok machine on remote and in the next second drop to 30 mA, wich is normally , the machine is in standby.
At this point everything looks fine , but dont know if the the 1.3-1.5 A are normally .
Here , on this topic someone mentioned about the brake booster, I will look for that one when aproach at the machine and also after 5-10 minutes after the machine is closed and locked, should hear that buzzing and clang clang release of pressure from hydraulic system.
I think could also be some relay with blocked contacts and power some electrical consumer.
I will keep update with may fail or progress on this issue.

 

Check out the post below.

 

The dc cut fuse is 25 amps they say. If removed steering angle and sonar has to be recalibrated they say. I don’t understand it. Because when the battery is replaced or cable removed, the sensors aren’t recalibrated. Pages 3 and 4. Every Prius from Japan goes through this process at the port. This is for a 2021. I don’t know why itonly 25 amp, seems low. Maybe this is something more like not to discharge the 12 volt while on the ship. Which leads to the answer all Prius are draining the battery while not being used.
https://static.nhtsa.gov/odi/tsbs/2020/MC-10178779-9999.pdf

 

After I replaced the old battery witj a new one and go to job, 10hrs later, the voltage were 12,4.Put on Ready jimp to 14 4, after 5 km drop to 13,7.
Hope that old battery was the root cause and dont need for a update on TSB, 2 volt missing is clear that 1 element inside is faulty maybe the acid evaporate.

 

this is a gen 5 thread. if you continue to have problems, please post in a gen 3 thread, or start a ne thread in the gen 3 forums.

 

Toyota's increasingly relying on the early adopters to do their testing? Likely the other manufacturers as well I suppose: it's a close race, and nobody wants to waste time doing any more than what's mandated, to ensure the product is ready for market, reasonably trouble-free. Couple that with stripping out stuff that used to be standard. And as a distraction, throw in ever more high-tech dreck.

 

you lost me at 'added a lithium battery tied into the system'

 

Three month update: no issues at 2,923 miles after a 12v battery replacement under warranty on March 14 at 829 miles.

 

Must be a bad batch. Happened on gen 4 too

 

Something to keep an eye out for:

TLDW - Some dealerships are installing trackers that pull juice from the OBD2 port. This is on the driver side, there are TWO screws for ours, then some push clips holding the kick panel on. Once the panel is released you can follow the OBD2 connector wiring up and see if it's hooked into an extension from a tracker. This could be the source of the drain for some people possibly.

Yes, the car in the video is a 2024 gr corolla not a prius, but it's all the same. Dealership can throw this on any vehicle they sell. Your dealership is not above being scummy. And I wouldn't be surprised if dealerships who have cars come back due to trackers killing batteries simply remove/replace the tracker and don't tell the customer the real reason for the drain (because no one wants to admit fault).

You can also pull the fuse (7.5a) for the OBD2 port.

 

Just going to say less scummy and more lazy.

The trackers are more often for inventory control on the lot. They run about $10 each, and the dealership gets a decent sized break on their insurance if they install them on all cars in inventory(helps in a big way for stolen vehicles). The problem is that the trackers are so cheap, it actually costs them more to remove them in labor than it does to just buy another. So a lazy dealership will just leave them installed when they sell the car.

Now if the car is financed through the dealership, they will almost certainly deliberately leave it installed as a recovery method if the owner defaults on the payments. In this case, there's likely small print in the financing agreement that requires the owner leave it alone. But if it's left installed on a car paid in full or financed through a third party, then it's likely just laziness.

But I will agree that they won't own up to it if the tracker causes battery problems regardless of the reason it was left installed after purchase.

 

This the one that was on mine, and is a common one the dealer puts on. I picked the seven year for illustration. I didn’t pay anything for it, the first original owner would have during the sales process. I just took the fuse out of the harness.
It helped the battery drain a little, but it’s still not like an alternator equipped car.

Amazon link didn’t post Spireon 7 year LoJack plan, $1250. Not $12.50, $1,250.