BMW E90 Auto-Dimming Mirror Coding: SPIEGEL_ELEKTROCHROM

On the E90, turning auto-dimming mirrors on or off is done with the SPIEGEL_ELEKTROCHROM parameter. Set to aktiv the mirror darkens under headlight glare from behind; set to nicht_aktiv it never darkens. The parameter sits in either the CAS or the FRM module depending on model year, so check both. What does SPIEGEL_ELEKTROCHROM do? An electrochromic mirror applies voltage to a gel layer inside the glass when the sensor behind it sees glare above a threshold, and the glass darkens. This parameter decides whether the car knows such a mirror is fitted. With the parameter off the car does not enable the mirror's automatic dimming, so the mirror, which drives the glass from its own sensors and electronics, never dims and behaves like ordinary glass. Enabling it on a car without the hardware achieves nothing. Module: CAS (2008, 2010) or FRM/NFRM (2006) Parameter: SPIEGEL_ELEKTROCHROM To enable: aktiv To disable: nicht_aktiv Function: automatic dimming of interior and door mirrors Prerequisite: an electrochromic mirror must be fitted Risk: low, fully reversible Which module and which years? The location of this parameter is not fixed, because the same name appears in two different modules. Community lists record it under CAS for 2008 and 2010, and under FRM for 2006. The sound approach is therefore to read your own car and see where the parameter actually shows up. • Marked in the CAS module for the 2008 and 2010 model years. • Marked in the FRM or NFRM module for the 2006 model year. • On some cars the parameter appears in both modules; set them to the same value. • Model-year coverage comes from community-compiled E90 coding lists; the binding source is your own car's FSW/PSW data. How do you code it? First find which module holds the parameter, then change the single value. OBDThink is an independent BMW coding and diagnostics app and is not affiliated with BMW AG. If you retrofitted a mirror, confirm its wiring is correct first; coding only tells the module the mirror exists, it does not create the connection. • Switch the ignition on without starting the engine; the mirror supply becomes live in this position. • Connect with OBDThink and read the CAS coding data first. • If the parameter is not in CAS, read the FRM or NFRM module instead. • Save a backup, then set SPIEGEL_ELEKTROCHROM to aktiv or nicht_aktiv. • Write the change, switch the ignition off and wait about a minute. • Test in the dark by shining a torch at the mirror from behind. Checking whether the mirror supply actually carries voltage in OBDThink is the fastest way to separate a coding problem from a wiring problem. How do you revert it? Reverting means returning the parameter to its former value. If you coded the mirror off and later want it back, setting the same line to aktiv is all it takes. Where a pre-coding backup exists, restoring it is always the safer option. Module: CAS or FRM/NFRM Parameter: SPIEGEL_ELEKTROCHROM Dimming off: nicht_aktiv Dimming on: aktiv Method: change the value and write, or restore the backup Check: in the dark, shine light at the mirror from behind, it should darken What should you check before coding? The most common situation is a fault that coding cannot solve. The gel filling in electrochromic mirrors can leak over the years, leaving a permanent dark stain in the glass that never clears. Switching the parameter off on such a mirror does not remove the stain, it only stops the attempt to dim. Fluid from a leaking electrochromic mirror can escape along the lower edge of the glass. Wash it off your hands and keep it away from the interior trim; it leaves permanent marks on fabric and leather. A leaking mirror is replaced, not repaired. What if the mirror does not dim? First confirm the mirror really is electrochromic, because the E90 also came with plain glass mirrors that look nearly identical. An electrochromic mirror has two sensors behind it, one facing forward and one facing back. If the rearward-facing glare sensor is blocked or dirty the mirror never sees the light behind it and stays clear; a blocked forward-facing ambient sensor has the opposite effect and makes the mirror dim more than it should. When the coding is right and the mirror still does nothing, the fault is in the mirror itself.