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?
