TIMM'S BMW E38
RAIN SENSITIVE WIPER REPAIR

If you have rain-sensitive wipers you should have the blue sensors that can be seen through the windscreen in front of the rear-view mirror. The blue bits aren't actually the sensors, they are glass lenses that are adhered to the windscreen and they do not come off (as far as I know), however, the control unit and the sensors proper do come off and can be replaced easily.

The fault usually shows itself when the wiper stalk is put into the automatic mode (first click up). In this position the wipers should do one wipe.....then stay parked unless it is raining, if the wipers continue to operate every 10 seconds no matter what position the sensitivity is set to then the sensor unit has failed. If the sensitivity control adjusts the delay time then you don't have rain-sensitive wipers!

Here is a Technical Document on the Rain Sensor System:

Rain Sensor System

The sensor / control unit can easily be replaced and is housed in the rear-view mirror housing. The cover on mine is different to the one shown in the TIS and is a single part (actually, looking at the photo, it does look like it comes in half, this can be separated once removed from the windscreen). Remove the outer case by pressing on both sides (I can only point at one side at a time!), pull the cover away from the windscreen and upwards at the same time, leave it dangling on the mirror stalk:

Under the cover can be seen the control module, it has a connector at the top centre, this is easier to disconnect once the control unit is removed. To remove the control unit pull out the two clips at the sides of the unit as shown:

Pull both clips right out and the control unit can be pulled away from the windscreen, disconnect the loom and the control unit can be removed leaving behind the glass elements on the screen:

Here is the control unit. It comes apart relatively easily, rather than just buying a new unit I thought I'd have a go at fixing it. So case off:



Here is the underside, the unit can be separated by removing two adjacent push-screws with a pair of side-cutters:



Here's the top of the unit once the PCB has been removed from the housing. You can see the IR transmitter pair on the left and the receivers on the right (there was a small white plastic mask which I removed):

A cusrory look didn't reveal any obvious problems, the only 'dodgy' looking bit was the metal bracket assembly which seems to have got a little hot where it meets the PCB, plus a bit of discolouration around the PCB. Nothing seemed broken though so I decided to clean the optics:

I then reassembled everything, the screws that hold the PCB in place just push back in with a bit of pressure from a metal tool. Snap the case back together and push the assembly back on the windscreen and push in the two clips at the sides. The outer cover just pushes back in position.

Result? Just the same I'm afraid. So, time to replace the control unit (part number 61356904012) and that cured the problem. However, I have seen many times that resetting the adaptations (INITIALISATION) via INPA sorted this problem - so it is well worth a try before buying a new unit or trying anything further.

 

Here is some more information that might be useful:



New units do NOT need coding
Second-hand units DO need coding
It is possible to reset the adaptation values with INPA, this may well get the system operating correctly again without the need to replace the unit.

Here is the full information from BMW:


Automatic Interval Control (AIC)
Function
With the aid of a rain sensor, the automatic interval control (AIC) system senses water or dirt on the windscreen and activates the windscreen wipers accordingly.

The AIC consists of an optical element bonded on the windscreen, to which an electronic evaluator is connected.

The system is active as of ignition lock position 1. The wiper/washer switch must be set to the first stage (intermittent wipe setting).

The wiper motor is activated by the general module of ZKE. The electronic evaluator sends the instruction to activate the wiper motor via the K-bus to the general module.



Optical element


The optical element is adhered to the windscreen behind the rear-view mirror. It consists of a glass body (prism) which routes the beams emitted by infrared diodes at a defined angle to the windscreen. The light beams reflected by the windscreen are routed by the optical element to the infrared receivers.

The optical element is heated by a heating element to ensure condensation cannot form on it.

The optical element is bonded together with the windscreen in a special process such as to guarantee the physical properties of the system. This bonding process cannot be carried out in the workshop. Therefore when replacing the windscreen, a special windscreen with the optical element already bonded to it must be used.

Electronic evaluator
The electronic evaluator is connected to the optical element by means of a catch mechanism.

It contains the electronic components as well as the infrared diodes and infrared receivers.

The instruction to activate the wiper motor is given via the K-bus interface.

Functional principle
Water on the windscreen is detected on the basis of the reflection of infrared beams.


When the windscreen is dry, all infrared beams which are emitted by the infrared diodes "S" and which hit the windscreen at a defined angle are reflected in full by the windscreen and therefore reach the infrared receivers "E" also in full.


A proportion of these beams is deflected by a drop of water on the windscreen (in the area of the infrared diodes). These beams no longer reach the infrared receivers "E".

In this way, the extent to which the screen is wet (or dirty) is determined dependent on the light intensity of the infrared beams and, if necessary, an instruction is sent via the K-bus to the general module of the ZKE III to activate the wiper motor.

Operation
To switch on the automatic interval control, the wiper/washer switch must be moved up to the first stage (intermittent wipe) and the ignition lock must be switched to position 1 or 2.

The automatic interval control system then controls the wipe intervals. If the windscreen is constantly wet (steady rain) the system activates continuous wiping in stage 1.

The wiper stage 2 can still only be set by way of the wiper switch (third stage).

Automatic interval control remains switched off if terminal R is switched off and on when the wiper switch is set to intermittent wipe. It is not activated before intermittent wipe mode is switched off and on.

The sensitivity of the rain sensor can be varied by means of the knurled wheel on the wiper/washer switch.

Note

There is no driving speed-dependent control of the wiper stages (reset of wiper stages when vehicle is stationary). In addition, the automatic fold-back function of the wiper motor has also been omitted on the E38 series (see functional description for windscreen wipers).

Operating conditions
The following conditions are necessary to ensure trouble-free operation of the rain sensor:

The windscreen must not be damaged (stone chips, scratches) or must not be heavily soiled (finger marks, streaks, wax film) in the area of the rain sensor.

The wiper blades must wipe the windscreen dry without streaks.

To ensure trouble-free operation, the windscreen should be cleaned regularly with a suitable wax-removing cleaning agent. The wiper blades should be replaced regularly.

Initialisation
The reflection characteristics of the windscreen depend on a large number of factors. In addition these characteristics also change as the windscreen ages.

During the initial wipe cycles, a new electronic evaluator determines the degree of reflection of the windscreen and stores this data in its non-volatile memory. From this point on, this data is constantly adapted to the windscreen which is subject to a certain degree of ageing over the course of time.

The stored adaptation values can be deleted with the diagnostic program (service functions). Renewed adaptation (initialisation) to the windscreen can then be carried out.

The initialisation procedure is described in the program sequence.

Initialisation is necessary:

After replacing the windscreen

When a used electronic evaluator is installed in a vehicle