Heat left/right outside rearview mirrors function

P88.79-2151-09

Shown on vehicle with code (581) Comfort automatic air conditioning

1 Circuit status

2 Circuit 61 (engine running)

3 Ambient temperature

4 Mirror heater request

5 Switch on/off mirror heater

B14 Outside temperature display temperature sensor

G2 Generator

M21/1 Left electrically adjustable and heated outside mirror

N22/7 Comfort AAC control and operating unit (with code (581b) Comfort automatic air conditioning)

N69/1 Door control module left

N69/2 Door control module right

N73 EIS [EZS] control unit

CAN-B Controller area network bus class B (interior compartment) (CAN B)

M21/1r1 Mirror heater

M21/2 Right electrically adjustable and heated outside mirror

M21/2r1 Mirror heater

N10/1 Front SAM control unit with fuse and relay module

N22 AAC control and operating unit (without code (581b) Comfort automatic air conditioning)

Function requirements

 Circuit 61 ON (engine running)

 Voltage not to high or too low

 Power window not operated

Function

The mirror heater (M21/1r1) in the left electrically adjustable and heated outside mirror (M21/1) and the mirror heater (M21/2r1) in the right electrically adjustable and heated outside mirror (M21/2) each consist of one heating resistor located on a foil on the rear of the mirror lens.

The AAC control and operating unit (N22) or the comfort AAC control and operating unit (N22/7) calculates the dew point from the outside temperature and the air humidity.

The mirror heater (M21/1r1, M21/2r1) is switched on and off depending on the dew point and outside temperature:

 Outside temperature  6 °C + dew point, the mirror heater (M21/1r1, M21/2r1) is switched on.

 Outside temperature  11 °C + dew point, the mirror heater (M21/1r1, M21/2r1) is switched off.

If no dew point is available, a substitute value of 13 °C is assumed.

If the outdoor temperature value received is not plausible, the mirror heater (M21/1r1 and M21/2r1) is switched on.

The request signal is relayed by the AAC control and operating unit (N22) or the comfort AAC control and operating unit (N22/7) to left door control unit (N69/1) and right door control unit (N69/2) via CAN-B (CAN-B). They supply voltage for the corresponding mirror heater (M21/1r1, M21/2r1).

 On vehicles as of 1.6.04 it is no longer possible to manually switch on the mirror heater (M21/1r1, M21/2r1) in combination with the rear window heater.