We are having a bit of a heat wave here in the midwest (110 heat index). I drove about 6 miles this evening and the engine did not shut off the entire drive. I had the windows down and the AC off. EV mode never kicked on and I was driving around 40 mph, even at idle the engine just stayed on. The battery bars were at mid level on the screen. The "energy" screen was not showing the engine running end not showing the main battery charging. It was really strange. I've never noticed this happening before. After I had the car off about 5 minutes, I got back in, drove home and the engine ran all the way home. Same issue with the energy screen. No charging showing at all. At home I let it idle in the driveway for a couple of minutes and still nothing on the energy screen. Does this sound like a symptom of a bad 12 volt battery? My car just turned 80k (2012) and the battery is original. I'm hoping that's all it is. I have an OBD scan tool. Would that give me any indication of the battery having issues? Nothing is showing on the dash in the terms of lights at all.
The hybrid system charges the 12V battery, so a bad 12V could cause the hybrid system to run more than normal trying to keep it charged. This is why you lose MPG when the 12V is going bad. I'm not sure you'll see any "arrows" during this mode, though, to give you any indication. Get your 12V battery tested. You're definitely at the end of the typical life span for a 12V. BTW, when replacing the 12V, pay attention to all the connections. There seems to be a "battery temp" sensor/wire that gets overlooked during 12V replacement, and this causes the HSD "arrows" to quit working. This just came up in other threads. Here's one, Energy monitor not working. Help please | PriusChat
I'll throw this out there as a likely scenario NOT involving the 12 volt. Did the car sit in the sun at all before your drive? If the HV battery temp exceeds ~113F, the car will protect the battery by not allowing EV mode and will run as you describe with no warning lights or codes. Blocking the HV battery fan vent or a clogged fan if the car is a pet hauler can yield the same scenario. If the HV battery was simply hot from the day, a drive this morning should show a return to EV capability.
I think that's exactly what happened. I just took it out for a drive and everything was great, EV came on and everything. It was hotter than hell here yesterday and the car was in the sun all day. Even with all the windows down, I think it must have been greater than 113. Fan area looks to be clear and clean since I don't have any terribly furry pets and rarely drive them anywhere. I feel a lot better now. I panicked too soon. Thanks!
I have a 2012 and I preemptively changed my 12v battery last spring. I might have gotten another year or two out of it and so incurred an opportunity cost of $20 or so. Well worth it to me.
If the HV battery was too hot, then this may have been contributor. Next time, close the windows, and turn the AC on. And for good measure, kick the Recirc off so that fresh air intake forces more cooled cabin air through the HV battery. This may help cool it enough that it can return to use.
