The PND screen won't change to the night screen when it is supposed to. Why?

Please check with the PND if its setting of "Turn day-time mode screen" is set to "ON". By setting it to ON, the screen changes to the brightness mode. Please also check if the illumination signal line of the vehicle is hooked up to AVN4430, and check the status of 'Link night view to headlight' setting. If not connected or status is set off, the display won't turn brightness down. Please check your owner’s manual for more details.