Radio at full volume at startup

I'll take a guess and suggest you check out the condition of the 12V battery. All sorts of strange electrical things begin to happen when that battery is on its last legs. Being a 2008 though, the battery has probably already been replaced at least once. Give it a check. It doesn't sound like a loose plug or damaged wiring sort of thing. I don't think I ever left the radio in my 2008 on when turning off the car. It should just come back on at the volume level it was turned off at, I would think.

 

That symptom would be a new one, but for more detail, OP should check here:
Weird stuff happening? MPGs dropping? Test The Battery | PriusChat

 

I agree with the 12v unless there's possibly a disgruntled significant other or a mischievous teen with access to the vehicle
A weak 12v manifests itself in unusual activity, I had the radio out of control myself, mine was after a dealer visit, 12v was good but they ran it down, prii are digital devices after all.

 

Or a hard-of-hearing dad.

The same one who kept shutting off the car with the windshield wipers up, so they would freeze overnight in an up position and try to break themselves when I started the car in the morning to go to school. I would always make sure the wipers were parked and off before shutting the car down, so the next day I could warm the car and get some engine heat on the defroster before trying to scrape the windshield and run the wipers. But dad was untrainable.

 

Did this fix your radio problem? I am having the exact same problem in my 2008 prius. Every now and then, when I turn the car on, the radio blasts out my ear drums. The volume is very loud and whatever music is playing sounds very distorted. Turning the volume knob has no effect on the volume of the car. The only fix I have found is turning the car off, waiting a while and then turning the car back on. If I turn the car off and do not wait long enough before turning the car back on, the problem still persists.

I tried the above proposed solution of checking the 12v battery, however all my voltages were within the normal ranges specified in the post. So, unless there are further tests that can be done on the 12v battery, it would appear that is not the problem.

Not sure if this is relevant to the radio problem, but I have noticed a drop off in MPG (40's --> 35). Additionally, I have been having issues with the keyless entry not working immediately when I put my hand on the door handle sensor. Furthermore, sometimes when I go to lock the car using the door handle button, the car thinks they key is still in the cabin of the car.

For the radio, I was trying to decide if I needed to replace the stereo head unit or perhaps the amplifier. But if I can get other suggestions that won't cost on the order of 100's of dollars, I would be ecstatic.



2008 Prius
JBL Speakers, w/o Navigation
100k mileage

 

you might need to load test the battery to be sure its good. lately I have seen several batteries (not prii) that would act like they were good-- the headlights were very bright and all the accessories worked fine until you tried to start the car. as soon as the starter was engaged the batteries would internally short and lose all power. let go of the key and the lights would come back on bright. since the prius doesn't have a strarter, a bad cell might cause different problems than a normal car.

 

congrats! thanks for the update.

 

We had a home mini stereo system that had a similar problem. As long as you used a remote to adjust volume it was fine, but do any adjustment with the set front knob, volume would start running up and up. Finally recycled it recently, wasn't seeing any use anyway.

 

I ended up having the local Toyota service center look at the issue when I was getting an oil change. I don't particularly have much confidence in their diagnosis, it kinda sounded like they didn't know so they just came up with something - however, I have not had problems with the radio since. They told me that I had the "ASL" button on (which stands for Auto Sound Leveling") and since turning it off, i haven't had a reoccurrence of the problem. I suppose I could see that if the code logic was poorly written and there was a bad microphone, then the ASL could potentially tell the audio speakers to turn up the volume an insane amount - but i don't see where the audio distortion would come from or why the volume knob would no longer work.