Hello everyone, this is a long story but I will try to keep things as short as I can. I've looked into this quite a bit in the last 24 hours but my cars symptoms seem to be somewhat unique based on what I've stumbled on.

On Saturday I was hauling my family in our 06 GX, about an hour into the drive while parked at a gas station every possible warning light came on. I took it to the nearest Napa to get the code read and test the battery level, battery appeared to be okay and the code I received was P0500 (speed sensor?). Our tesla-style screen went blank, speedometer quit working and the heat came on full blast. All very weird stuff, especially according to the code that was pulled.

I took it straight to our local Toyota dealership, I usually work on my own vehicles but I wanted to get this checked out by actual pros. Toyota called later me to inform me that it was bad bad diode in the alternator and it was overcharging the battery (up to 19V indicated on invoice) and that it needed replaced. Our car just turned over 200k and I had planned on doing our timing belt in the next few weekends myself but decided to have them do it while they were in there since it saved on labor costs and this is our family vehicle.

Everything gets fixed, we pick the car up Tuesday afternoon and it's driving great again, no warning lights and nothing weird. After about 50 miles of driving the audio volume started to fade and couldn't be turned up, and the rear DVD screen also shut down at the same time. I tried turning the key to reboot the electronics but that didn't help, no volume at all but everything else on the center screen was working just fine. The sound comes back on intermittently after going crazy and it seems to be while the car is coming to a stop, when I hit the gas the volume will decrease in proportion to the amount of gas you're giving it and then go completely silent again.

I take it back to the dealership and they were at a complete loss. While parked in the service bay at Toyota I showed them that the volume was turned up and when I gave the car gas the sound would die down with it, once it got back to idle the sound would be normal. The alternator and battery are testing within the levels they should be according to them. I've read a few other posts where people have *no sound* or their car will play sound briefly on start and then immediately go away. This issue points toward a bad AMP from what I have read. So far the audio appears to work just fine until around an hour-ish of driving and then it spazzes out.

Is the most likely scenario here that the overcharging made the AMP go haywire or is there anything else that somebody can think of? Does the rear DVD screen even get power from the AMP? This morning, the sound/volume died again but I tested the rear DVD screen and it appeared to be working this time. All fuses appear okay and the screen is otherwise still working just as it did. Electronics are not my jam.

 

If the voltage really did go up to 19 that could be enough to damage electronics especially if it was more than a brief spike. If you don't have a volt meter get one and test the voltage (car running of course) yourself to see if it's okay.

 

I tested it with a multi-meter just now. At idle it was at 14.18, I had my wife hold it at 2k rpm and it went up to 14.22 then settled back to 14.18 at idle.

Yesterday at the dealership when they tested it, they said it was 13.93 at idle and then 13.98 while I was giving it a little gas. I am using a very cheap tool vs their nicer one so that could perhaps be skewing the results a bit.