I inherited my 07 Prius a few years back and have had no end of issues. Notably, last winter the car threw the red triangle while driving and wouldn’t start after I pulled it over. All kinds of hybrid system codes. I replaced the inverter pump, because it wasn’t running. The car worked for a week after that until it suddenly wouldn’t start one particularly cold morning. In the late spring I jumped it, let the 12v battery charge and had no issues with her all summer until we got into freezing temps in October. The car again wouldn’t start, and has been sitting since. On Wednesday, Thursday, and Friday this week, I’ve jumped it, let it sit all day and drove around in the evening. And the following morning it won’t start. Last night I read the 12v battery at the correct voltage, but it was 9.5v this morning, showing why it’s not starting. Now the previous owner had replaced the battery 3 times in less than 3 years, but they also let it sit a lot. Before I go down the same road of replacing batteries annually, is there any way I can rule out the possibility that the inverter isn’t charging correctly?
To check if the DC/DC converter is working and charging the 12v battery, you need to get the car running. Jumpstart the car and get it running. Then, use your meter and check the voltage at the jump point in the fuse box in the front under the hood. If the DC/DC converter is working, you should measure 13v or higher.
That’s really convenient. I was worried I’d have to crack into the assembly to check the dc/dc converter. So you mean test the voltage across that positive node in the fuse box and any ground?
Your best bet is to actually check the voltage at the battery terminals in the trunk of the car where the battery is on a car in the ready mode running not necessarily the ice engine running but the car ready You should see 13.5 to 14.5 volts on the 12 volt battery at that time the higher the better usually it's around 13.7 13.9 something right in there If the battery is really low or something or starting to get worn out it may be around 14.4 or even 14.5 that indicates the DC to DC converter is working relatively well voltage wise the DC to DC converter doesn't have much rear end behind it so you should keep a battery tender cord in the trunk connected to the battery drill a hole in the plastic panel then just leave it coiled laying there and every few months you look at it you'll think oh yeah I need to tender my battery and you should in this particular type of setup.
When the car was running I measured 13.8 V across the 12 V battery in the trunk. I got nothing from the node in the fuse box. After I shut it off, got 3.9 V on the battery. And the car was making a high pitched whine until I tapped the brake. Even after that it was making this clicking sound around the fuse box area https://youtube.com/shorts/_enYHNF2P-c?si=lSfVX5NJwhCbLgC4 Either way, I should feel confident in the converter?
Yeah your car is going crazy with that 3.9 volt business exactly right nothing really too odd about that so fix the 12 volt battery and make it 12.3 to 12.7 because that's what that type of battery should show AGM of this group size and you'll be done with all that I guess The unstable 12 volt will make all kinds of stupid nonsense go on You can go round and round with this and play all these games all you want but until you have a solid 12 volt system that can bus will not be happy and not operate correctly you'll have communication issues and you'll be here and not driving pretty much
If you drive the car "regularly" (more than an hour each week) and still have problems with the 12V going dead, then you might need to have the car tested for excessive "key off" draw. Posted via the PriusChat mobile app.
+1^ Each successive draw-down will weaken and kill any battery. IMHO, you need to install a battery blanket and a smart RV battery maintainer. Wire them together, so you only have one plugin. Leave it plugged in, so it'll run when you need it to. That cold will also effect the traction battery pack. Hope this helps....
The blanket doesn’t look like a practical solution for my circumstance, but I will get to testing the key-off draw ASAP. In the meantime I’m monitoring this new one manually
Then install one of these: Vgate Battery Monitor BM2 Bluetooth 4.0 Wireless Battery Load Tester Analyzer | eBay Bluetooth enabled, you just stand next to the car. You can jump and recharge from the jump point under the hood - But I wouldn't exceed 6-8 amps, since your shooting power throughout the car's wiring system. DO NOT mix up the polarity!!! great way to fry something!!!!
