Toyota Windom Audio Stereo system volume low?

Hi there,

I have a 91 Toyota Windom that was imported from Japan. The audio stereo system works but the volume is quite low even when you turn the volume control diag to full.

I guess it may have something like loudness mode that is activated, which is suppressing the volume level.

Can anyone let me know if there is a loudness mode in this audio system? If so, how to de-activate it?

Also what is the default PIN for the audio system in case I needed to disconnect the power from the system where the PIN will be needed to unlock it.