Vehicle: 2007 Toyota Prius (standard trim) Problem The entire audio/entertainment system won’t power on. On the MFD’s Audio screen, I only get an “Audio Off” message. Background & Research I couldn’t find many reports online, but one Reddit thread noted a Prius radio died after the 12 V battery went flat. Someone in the comments fixed it by pulling fuse #17 in the engine compartment, then reinstalling it to power-cycle the system. Initial Troubleshooting Replaced engine-bay fuse #17 (15 A). Radio returned immediately. Next day: audio dead again. Pulled and reinserted fuse #17—radio powered on, but only until the following day. Battery history: the 12 V battery has gone flat multiple times from long periods sitting. Update 1 Replaced three fuses that feed the audio/MFD/clock circuits (all tested good for continuity despite the old blades showing oxidation and heat discoloration): Engine compartment #17 DOME, 15 A Passenger-compartment #17 PANEL, 7.5 A Passenger-compartment #24 ACC, 7.5 A After replacing, I cycled the engine and door locks twice (to mimic leaving and returning)—the radio stayed on. I’ll report back if it still works tomorrow. Related Fuses Engine Compartment 17 DOME 15 A Audio system, interior lights, smart-entry/start, gauges, turn signals, luggage light, clock Passenger Compartment 17 PANEL 7.5 A Multi-information display, clock, audio system, instrument lights Passenger Compartment 24 ACC 7.5 A Audio system, multi-information display, clock Question: Given the symptom returns after a day and the battery has discharged several times, what’s the most likely cause? Similar issues reported here: 1. 2. Radio / CD stopped working | PriusChat
Update 2: Bad news, I went to start the car today and the radio still wasn’t working. At best, cycling power by pulling the fuses only restores it until the next day. There’s absolutely no power to the head unit—even the CD-eject button does nothing. Could this be a fault in the radio/CD unit itself, a wiring issue, or something else?
hard to determine. you might have to pull it out and check the voltage. maybe it is shutting itself off, an electronics repair company might be able to fix it.
Update 3: To rule out a stuck relay, I measured the 12 V at the accessory power outlet with the car in ACC mode and saw just 10.2 V. Then I switched the car to ON mode (powering up the electronics and engaging the DC–DC converter), and the voltage rose to about 14 V, at which point the radio came on. Low ACC voltage points to a failing 12 V battery (I’m surprised the electronics powered at only 10.2 V), though a wiring issue can’t be ruled out. Next, I’ll check the battery’s resting voltage at the terminals and, if it’s similarly low, try a reconditioning cycle. If it turns out to be an internal problem with the radio, I’ll probably just replace it with another factory unit. It’s not worth repairing, especially since the tuning knob’s spring is missing. I’m more concerned about a wiring-harness fault, but I’m starting to think it’s a bad battery, which is also expensive but much easier to replace.
Update 4: I measured 10.5 V at the battery terminals. I then charged it fully over four hours with a 12 V charger. After waiting 15 minutes, accessory-mode voltage read 12.6 V. The next afternoon, accessory-mode voltage had already fallen back down to 10.3 V (9 V under load). I’ve disconnected the battery again and will run the charger’s Repair mode for a few hours. Questions: How dangerous is driving the Prius with a battery like this? What's the best value option for a replacement considering the car is sometimes left parked for weeks at a time?
there's no danger except that it may not start at an inconvenient time. no battery likes to sit. you should disconnect the negative or put a maintainer on it. the correct battery is agm with an outside vent, and not cheap. people use all and any kind of 12v to save money. you might have to alter the hold down clamp, or even the base that it sits in to keep it secure. then it just depends on your risk tolerance, since the battery is off gassing inside the cabin with you.
It dropped back down to 10.5v again after 4 hours of pulse charging, so one of the cells is effectively 0 volts. It's almost certainly an internal short and I guess pulse charging isn't going to bring it back. Everything "works" because the ECU and relays can handle 9-9.5v for a short period of time until the traction battery starts supplying 14v. My guess is the radio, or the circuit powering the radio is a bit more sensitive to low voltage, so it doesn't power on when the voltage dips on startup. It's hard to find a battery under 200 dollars. OEM battery details are: S46B24R,W(SMART ENTRY) Part Name Code: 28800 Replaced By: 28800-21172 Current shorted battery is a "Truestart". Truestart batteries are available at autoparts.toyota.com, but it's pick up only at a dealer. OEM battery at Toyotapartsdeal.com (does not specify brand) are sold for a truly disgusting $350. Ebay has various sellers with 46B24R LiFePO4 batteries listed as replacements for Yuasa HJ-S46B24R for $400. The description says they are a drop in replacement for lead acid, but also not to use a lead acid charger. They ship from China, so there is also a long wait and effectively no warranty. Yuasa HJ-S46B24R is listed on Ebay for $200, and may be available as cheap as $180 elsewhere. Essentially, it looks like my only reasonable options are another Truestart battery or a Yuasa, although I could "upgrade" to a LiFePO4 battery, but it seems wasteful considering the condition of the rest of the car. I found a similar battery for 120 dollars, but it would apparently require some washers and longer bolts, possibly adapters. With the time and hassle of trying to fit everything together, I'm not sure it's worth the 60 dollars minus the cost of hardware saved. I feel like a tool spending 200 dollars on a lead acid battery, but I went with another Truestart. I actually think the LiFePO4 is probably a better value long term, but 400 dollars is just insane. Is there a low cost solar tender/charge controller that is safe to use with the battery connected and can be fixed to one of the small quarter panel windows?
As you have bought a replacement, this is moot for you, but for others who come along later, you should be able to find at least two aftermarket batteries just by using S46B24R as the search term. The Truestart sold by Toyota are made for them by Yuasa. AGM batteries (of the same Ah spec) are more expensive than old-school Pb/Acid flooded batteries and there are reasons for that related to their construction. AGM have a better deep cycling profile when compared to flooded batteries. Generally speaking, you get what you pay for.
idk anything about solar battery maintainers, i guess i would just google around. no place to plug in with an extension cord?
looks like you need a decent size. maybe place it on the dash or in the hatch depending on where the sun is? ref=sr_1_1_sspa ref=sr_1_3 everyones-thoughts-on-best-size-solar-panel-to-maintain-12v-car-battery-year-round.65209 idk how many watts the prius draws when off
