Sound issue after new head unit

[BOFFROAD]

I installed a Joying android head unit with a Metra tyto-01 harness so that it would work with the JBL factory amp. All the speakers work and it sounds fine at low volume, however the max volume is about have of what the factory setup used to do and the speakers begin to distort very early.

 

[BOFFROAD]

You have to take the aftermarket hu out and put the stock one in, then reset all the controls and remove it and reinstall the aftermarket unit. I don't think just unplugging things will work. The way the stock stereo works is that the hu basically controls the levels to the amp digitally. For instance, if one were to leave the volume control set at zero when removing the radio, you would have very little volume when you put the aftermarket hu in. I know bc I messed mine up the first time due to not reading the instructions! Its easy to remove the stereo, but do you have the stock hu?

I just read this, it makes sense to me but would like to have more input.

 

[overfedfish]

Return it

 

[AuSeeker]

If you read through this topic.....

http://www.toyota-4runner.org/4th-gen-t4rs/160083-scion-frs-radio.html

I saw mention of before removing the stock HU set the volume at 75% and then install new HU, I just briefly scanned the topic a couple of days ago, so if you look harder you should find your answer, but from what I saw from my brief look it comfirms what you saw in the post you quoted.