Grant - usenet poster
Rank: Apprentice
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Below is a description of the '04 Malibu DIC brightness control. Probably
the same for your '05. As another poster has said the dealer is likely your
best hope.
Radio Data Link Communication
The radio communicates with other modules via the GMLAN data bus which is a
CAN based protocol. This vehicle uses 2 variants of the GMLAN data bus. The
variants are a low speed and high speed vehicle bus. The radio connects to
the low speed vehicle bus which runs between 12.5-40 kbps.
Radio Head Unit Dimming
Dimming and backlighting levels are determined by the GMLAN signal data the
radio receives. The radio sets the backlight and Vacuum Fluorescent display
dimming to the value indicated by the interior dimming level and interior
dimming display level signals in the GMLAN dimming information frame.
The radio provides faceplate and control/graphics backlighting in the OFF
(RAP inactive) when the exterior lighting Virtual Network is activated. The
radio display is consistent then with the surrounding devices that use
analog PWM dimming to backlight their control/graphics when the power mode
is OFF and the park lights are ON.
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