GM Service Manual Online
For 1990-2009 cars only

Power Mirrors

The LH mirror switch circuit provides input to the LH Door Control Module (LDCM) when the LH mirror switch is pressed. This input allows the LDCM to detect a mirror UP, DOWN, LEFT or RIGHT request from the LH mirror switch. The LDCM provides both power and ground to the mirror switches. When the LH mirror UP or DOWN switch is pressed, a ground is supplied through the LH mirror up or down switch to the LDCM mirror up or down input which is pulled low. When the LDCM detects low voltage on the LH mirror up or down input, the LDCM will command the mirror verticality. If the LDCM detects low voltage on the LH mirror left or right input, the LDCM will command the LH mirror horizontally. If the RH mirror is selected, the LDCM will send a message on the serial data line to the RH Door Control Module (RDCM) to operate the RH mirror in the direction selected by the LH mirror switch. The DCMs provide both power and ground for mirror output control through the vertical and horizontal mirror motor control circuits. The direction of the mirror motor is determined by the polarity of the voltage applied to the mirror motor.

Heated Mirrors

The DCMs control the heated mirror functions. The LDCM supplies power and ground to the LH heated mirror and the RDCM supplies it to the RH heated mirror. When the DCMs receive a message on the serial data line indicating the rear defogger was turned ON, both DCMs will activate the heated mirror by applying voltage to the heated mirror element feed circuit.

Memory Mirrors

The Door Control Modules (DCMs) can recall mirror positions. The DCMs receive mirror position signals from the mirror horizontal and vertical position sensors. These signals are used by the DCMs during memory recall to determine the horizontal and vertical positions of the LH and RH mirror. The DCMs command the memory mirror settings based on the voltage level received from the horizontal and vertical position sensors. The DCMs provides a 5 volt supply and ground to the sensors. The vertical and horizontal position sensors are variable resistors which monitor the voltage level across a signal circuit. When either of the memory switches is pressed, a ground is supplied through the LDCM, pulling the memory switch low. When the LDCM detects low voltage on a memory input, it will activate the appropriate memory function, which also sends messages on the serial data line to other systems responsible for memory recall functions (RDCM, radio, seats, etc.). When the LDCM sends a memory recall message on the serial data line, the RDCM will command the RH mirror to the appropriate position.

For information on programming the memory mirrors, refer to Driver Personalization in Personalization.

Mirrors -- Outside Automatic Day/Night Feature

The automatic day/night feature of the driver outside rearview mirror is controlled by the inside rearview mirror. The inside rearview mirror supplies a signal and a low reference to the driver outside rearview mirror. The voltage on the signal circuit of the driver outside rearview mirror varies between 0.5 to 1.5 volts depending on light conditions present at the inside rearview mirror. At night, with the automatic day-night feature enabled, the driver outside rearview mirror will automatically darken with the inside rearview mirror to reduce the glare from the headlamps from behind. The voltage on the signal circuit of the driver outside rearview mirror will be near 1.5 volts. In the daytime, the mirrors are in a normal state. The voltage on the signal circuit of the driver outside rearview mirror may be less than or near 0.5 volts. Refer to Automatic Day-Night Mirror Description and Operation in Stationary Windows for further description and operation of the inside rearview mirror.