Rain sensor not sensitive enough

[gnl]

Anyone have this problem with the rain sensor?

Z4 3.0 sdrive 2009.

Rain sensor seems to lack sensitivity generally and sometimes hardly works at all. It switches on and gives one wipe and the stalk light comes on. Often at the start of a journey it hardly operates at all. I need to initiate manual wipes to be able to see! After a while it starts to wipe more frequently but there are still often times when I need to do manual wipe to see properly. It’s in the ‘2’ setting on the stalk.

Is this a common problem? Can it be made more sensitive or does it need a new sensor? If so is it easy to change? I’ve tried cleaning the screen where the sensor is and the sensor looks clean inside.

Ideas? Thanks

 

[Vonlipvig]

Not sure if it's right, but mine is exactly the same. When you want it intermittent with light rain it hardly works at all. Heavier rain when it goes on constant works pretty well, it's the intermittent that's poor. I would rather have the button press as a standard intermittent if I'm honest with no automatic

 

[brillomaster]

isnt there sensitivity adjustment for the intermittent setting on the stalk? my E90 BMW has i think, 5 sensitivity settings for the automatic wipers.

though that said, even on the most sensitive setting, it doesnt respond well enough to the common british drizzle... completely unnecessary automation IMO, would much rather the 5 sensitivity settings were just manual adjustments on the speed of the intermittent wipe.

 

[buzyg]

... completely unnecessary automation IMO, would much rather the 5 sensitivity settings were just manual adjustments on the speed of the intermittent wipe.

 

[obewan]

isnt there sensitivity adjustment for the intermittent setting on the stalk? my E90 BMW has i think, 5 sensitivity settings for the automatic wipers.

Mine has 3 settings. Generally I leave it on the lowest sensitivity and it's perfect for me personally
Exception to that is I've noticed that the windscreen has to be fully demisted before it works consistently

 

[gnl]

It’s on the most sensitive setting. Strangely it is definitely worst at the start of a journey. Once the car is warmed up it seems to respond better but still not as good as hoped.
I don’t know if this is to do with the glass or sensor temp of something else. Seems like I’m stuck with it from comments.

 

[Ed.Straker]

Maybe its the onboard heater in the unit see BMW's tech advice..

Rain sensor
The rain sensor is an optical system. It consists of an optical element bonded on the windscreen and an electronic component. Alongside the evaluation electronics, 4 optical transmitter and receiver diodes are integrated in the electronic component.

When the rain sensor is activated, visual acknowledgement is given to the driver in that one wiping cycle is executed first. Then, the transmitter diodes emit an infrared light which is guided across the optical element to the windscreen. If the windscreen is completely dry and clean, the infrared light is fully reflected to the receiver diodes.

If there is water or dirt in the area of the optical element on the windscreen, full reflection of the infrared light is no longer possible. Part of the light penetrates the windscreen so that only part of the light arrives at the receiver diodes. The evaluation electronics identify the level of windscreen wetting from the reduction in light quantity and transmits a signal via the K-CAN data bus. The wiper module then runs a wipe cycle. In the case of heavy rain, intermittent operation shifts into the continuous wiping mode.

A heating element integrated in the rain sensor prevents misting of the optical element or the diodes.

The sensitivity of the rain sensor can be varied in 4 sensitivity stages by means of the knurled wheel on the wash/wipe switch. Each time the knurled wheel is moved in the ”Increase sensitivity” direction (upwards), a wipe cycle is carried out.

When the vehicle is at a standstill, there is an automatic reduction of the sensitivity so that the wiper usually runs in intermittent mode.

If the rain sensor fails, the wiper runs at a fixed time interval.

Prerequisites for trouble-free operation of the rain sensor are:

Wiper blades OK
Sensor area free of soiling (road salt, insects)
No streaking on the windscreen
Windscreen in the area of the rain sensor without faults (stone chipping)
Optical element bonded free of bubbles with the windscreen glass

 

[gnl]

Maybe its the onboard heater in the unit see BMW's tech advice..

Rain sensor
The rain sensor is an optical system. It consists of an optical element bonded on the windscreen and an electronic component. Alongside the evaluation electronics, 4 optical transmitter and receiver diodes are integrated in the electronic component.

That’s interesting. I had a sense that it seemed to improve after it had ‘warmed up’ but couldn’t understand it as I didn’t realise it actually needed to warm up! I’m now suspecting it could indeed be the heater has failed and misting is stopping it working until the car/screen warms up.

I’m guessing that the heater can’t be replaced and it will be a complete unit and also guessing that being that it’s bonded to the screen it’s not a diy job. It’s sounding expensive and prob not worth it. Unless anyway can suggest otherwise.

 

[mr.tourette]

always been shite on any car I've had, and proper annoying on a daily if you're having to scrape ice off and the sodding things fire up every time one of the worst automated ideas on a car

 

[Pondy]

always been shite on any car I've had, and proper annoying on a daily if you're having to scrape ice off and the sodding things fire up every time one of the worst automated ideas on a car

Agree with that. Rain sensing wipers are shite. Period. I've had five cars with them (Merc, Mazda, Volvo, Honda) they're all terrible.

Same with auto headlights; if it's foggy forget it!

 

[flybobbie]

Friends Land Rover, parking dist. kept sounding. When we got to destination we had a look. Wasp was splattered on a sensor.

 

[mcbutler]

Maybe its the onboard heater in the unit see BMW's tech advice..

Rain sensor
The rain sensor is an optical system. It consists of an optical element bonded on the windscreen and an electronic component. Alongside the evaluation electronics, 4 optical transmitter and receiver diodes are integrated in the electronic component.

That’s interesting. I had a sense that it seemed to improve after it had ‘warmed up’ but couldn’t understand it as I didn’t realise it actually needed to warm up! I’m now suspecting it could indeed be the heater has failed and misting is stopping it working until the car/screen warms up.

I’m guessing that the heater can’t be replaced and it will be a complete unit and also guessing that being that it’s bonded to the screen it’s not a diy job. It’s sounding expensive and prob not worth it. Unless anyway can suggest otherwise.

You couldust tap your screen with a hammer, crack it and then get a free replacement. Most decent insurance companies offer free screen replacement without affecting no claims or NCD.

 

[brillomaster]

hmmm probably not a good idea to intentionally damage your vehicle to claim on insurance, sounds like insurance fraud to me... poor rain sensing wiper performance isnt bad enough to risk a fine and have insurance cancelled...