Just checking my rain sensors for the wipers and the auto lights function.

Read the owners manual and understand, I think, how they are supposed to work however I seem to have some issues and wondering if my understanding is wrong or something is wrong with the sensors.

My understanding is:
Rain Sensor Wipers -
With both the headlight switch and the wiper switch set to auto, when wipers are turned on in position 1 or 2 for at least 20 seconds the headlights come on and remain on for 2 minutes after the wipers are turned off - This works correctly, no issues

With the wiper in Auto and set to intermittent mode, when it rains the wipers come on - this does NOT work. With the car running and everything set as described I sprayed the windshield with a hose and no wipers, also this morning while driving at around 50mph in light rain the wipers did not come on.

Auto Headlights -
With the headlights set to auto, when the light sensor in the back of the mirror detects low light the headlights come on. Checked this tonight and it works. However if I turn the lights off, with the car running, in gear, at night, I should get a warning indicating the lights are off, this does NOT work. Also I taped over the light sensor with several layers of electrical tape during the day time and the headlights did not come on with the switch set to auto, car running and in gear, no warning either, however the rear view mirror did auto darken when I covered the light sensor on the back. If I turned the mirror off or remove the tape it returned to normal.

Any ideas what might be going on?

Also what is the round sensor on the dash drivers side close to the windshield? for?

 

The rain sensing system detects differing levels of rainfall and varies wiper operation ranging from intermittent to maximum continuous. It is brought into operation by selecting AUTO on the wiper control switch bezel.

JTIS gives the following description of how it functions:

The system consists of a rain sensor, an electronic control module and a dedicated wiper control switch.

The rain sensor is an optical transducer that is sensitive to changes in infra-red light penetration of the windshield created by the refractive effects of water droplets.

The sensor elements consist of two groups of light emitting diodes which alternately project infra-red light onto the windshield and a photo-diode that receives resulting reflections from the glass. All of the infra-red light is reflected back from a moisture-free windshield, resulting in a constant 5V output signal from the sensor and no wiper activation. Rain falling on the light sensing area of the windshield results in refraction and diffusion of a proportion of the projected light with a corresponding imbalance of light received by the photodiode. This results in pulsed outputs from the sensor, the frequency and duration of which are directly proportional to the number and size of water droplets respectively. These pulses together with wiper switch position signals are received by the sensor control module and processed to mimic column switchgear operation. In this recognisable form, signals are input to the body processor module (BPM) where they are interpreted as normal wiper operation requests.

I leave my AUTO sensing OFF because on my X300, X308, both XK8's and current XK, I found it too sensitive, tending to drag the wipers across a barely wet windscreen.

The majority of issues with both rain sensing and auto headlights that are reported on the forum are found to be caused by faulty sensors in the mirror and not the modules.

The round sensor on the dash is the Solar Sensor - one of the five sensors in the AC system.

Graham

 

For 4.2 cars the auto headlight sensor is fitted to the windscreen below the rain sensor.

 

Aha...that would explain why covering the sensor on the back of the mirror did not turn on the lights.

But it looks like my rain sensor may be bad...o well...guess I'll have to go old school and turn the switch on manually.