GM Service Manual Online
For 1990-2009 cars only

Power Mirrors System Components

    • Outside rear view mirror switch
    • LH outside mirror
    • RH outside mirror
    • Mirror 10A fuse
    • Memory mirror module (w/A45)

Outside Power Mirror Operation (w/o A45)

Each outside power mirror has 2 reversible motors. One motor adjusts the mirror view left and right - horizontal, the other motor adjusts the mirror up and down - vertical. The driver selects which mirror is moved by placing the mirror select switch in either the L or R position. The driver then operates the mirror switch in one of the following positions in order to control the polarity of the battery voltage applied to the mirrors:

    • UP
    • DOWN
    • LEFT
    • RIGHT

Battery positive voltage is applied from the underhood fuse block MIRROR fuse (10A) to either the left or right power mirror. As the mirror switch is operated, battery voltage and ground is supplied through the contacts of the switch.

Outside Power Mirror Operation (w/A45)

The memory mirror module (MMM) controls the memory mirrors by controlling the movement of the mirror motors. The LH mirror and the RH mirror each have 1 motor for Up or Down movements, and 1 motor for Left or Right movements. All of the motors operate independently of each other. Each motor has an attached position sensor.

The underhood fuse block MIRROR fuse (10A) supplies battery positive voltage to power the MMM and the mirror motors.

Mirror Position Sensor Operation

The position sensors are used by the MMM in order to perform the following functions:

    • Store the motor positions in memory.
    • Return the motors to the stored memory positions.

The mirror position sensors are potentiometers that are mounted to each mirror motor's transmission cable. When the cable rotates, the resistance of the potentiometer varies. The feedback voltage is monitored by the MMM in order to determine the motor position. The sensor feedback voltages vary from 0.25-4.75 volts. When a set memory command is executed, the MMM records and stores the motor positions by recording each position sensors feedback voltage. When a memory recall is commanded, the MMM moves the motors until all of the position sensor feedback voltages equal the voltages stored in the memory.

Memory Set Operation

When the MMM receives inputs from the memory set switches, the MMM records the feedback voltages from the 4 mirror position sensors for the appropriate driver. The MMM sends a Class 2 message to the memory seat module (MSM). This action informs the module of the SET MEMORY command.

Memory Recall Operation

The MMM applies the battery positive voltage to the mirror motors until all of the mirror position sensor feedback voltages equal the feedback voltages stored in memory for the appropriate driver. The MMM also commands the MSM to perform the memory recall function via a Class 2 message. The MSM then applies the battery positive voltage (B+) to all of the seat and lumbar support motors until the position sensor feedback voltages equal the feedback voltages stored in the memory for the appropriate driver.

Heated Mirrors Operation

When the rear defogger is turned ON, the instrument cluster (IPC) confirms that the engine is running. The IPC receives engine status from the powertrain control module (PCM) via the class 2 serial data line. When engine status has been confirmed, the IPC turns ON the rear defogger-ON LED and commands the body control module (BCM) to turn ON the rear defogger relay via the class 2 serial data line. When the BCM grounds the rear defogger relay coil, the relay energizes applying battery positive voltage to the HTD MIR Fuse (10A). The HTD MIR Fuse provides battery positive voltage to the heated mirrors.

Automatic Day/Night Feature Operation

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.