Automatic Day/Night Mirror - Operation

OPERATION

The automatic dimming inside rear view mirror is also known as the ElectroChromic Mirror Module/ECMM. A thin layer of ElectroChromic (EC) material between two pieces of conductive glass make up the face of this mirror. Two photocell sensors allow the ECMM circuitry to monitor light levels and automatically adjust the reflectance of the mirror glass.

An ambient photocell sensor is located on the forward-facing (windshield side) of the ECMM housing, to detect the ambient light levels outside of the vehicle. A headlamp photocell sensor is located inside the ECMM housing behind the mirror glass and faces rearward, to detect the level of the light being received at the rear window side of the mirror glass. When the circuitry of the ECMM detects that the difference between the two light levels is too great (the light level received at the rear of the mirror is much higher than that at the front of the mirror), it automatically begins to darken the mirror.

The ECMM operates on battery current received through a fused ignition output (run) fuse in the Junction Block (JB) (also known as the interior Power Distribution Center/PDC) and has a path to ground at all times through a takeout and eyelet terminal of the body wire harness secured to the body sheet metal. These connections will only allow the ECMM to operate when the status of the ignition switch is On. A green Light Emitting Diode (LED) unit illuminates through the face of the ECMM housing to provide an indication whenever the automatic dimming feature is enabled.

The Local Interface Network (LIN) slave node circuitry integral to the ECMM allows it to monitor electronic reverse switch status messages received over the LIN data bus. This input allows the ECMM to automatically disable its self-dimming feature whenever the vehicle is being driven in Reverse. On vehicles equipped with the optional SmartBeam(R) Automatic High Beam Module (AHBM) and digital imager camera, the AHBM also communicates with the BCM over the LIN data bus through the LIN slave node circuitry of the ECMM.

The hard wired inputs and outputs for the ECCM may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the EC mirror system or the electronic controls and communication between other modules and devices that provide some features of the EC mirror system. The most reliable, efficient, and accurate means to diagnose the EC mirror system or the electronic controls and communication related to EC mirror system operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.

OUTSIDE MIRROR - The driver side automatic dimming outside mirror is operated by the same controls and circuitry as the automatic inside rear view mirror. When the automatic inside rear view mirror is ON or OFF, the automatic dimming outside mirror is likewise ON or OFF. Just as in the automatic inside rear view mirror, a thin layer of electrochromic material between two pieces of conductive glass make up the face of the automatic dimming outside mirror. However, the signal to control the dimming of the outside mirror is generated by the automatic dimming inside rear view mirror control circuitry based upon the inputs from the two photocell sensors integral to the inside mirror. That signal is then delivered to the driver side outside rear view mirror on two hard wired circuits.