Rear wiper

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rj3series

Member
Joined
May 8, 2015
Messages
11
Does anyone else see the following behavior from their i3 regarding the rear windshield wiper: When the switch is turned to the "on" position on the stalk (i.e., rear wiper switch flicked forward), the rear wiper works perfectly well. After the car is shut down and restarted, however, with the switch still in the "on" position, the rear wiper does not activate. It is only when the wiper switch is returned to the off position and then turned back on by flicking the rear switch forward that the wiper actually works again. Is this an anomaly affecting only my car or is this common to the i3 platform? I find this frustrating when it is raining during two consecutive journeys because it requires that I flick the switch back and forward the second time, even though it is already starting in the "on" position as a result of the prior wet journey. Note that I am not referring to the front wiper in this post at all. Thanks.
 
I hadn't noticed that, but it sort of makes sense knowing how the car's electronics work.

Almost (if not) all switches in a modern BMW do not actually turn things on/off directly...when moved, they send a message to the computer, and the computer makes the desired function happen. The car tends to remember the setting of many when you shut it off. It appears that the state of that switch is not stored in non-volatile memory, so is lost when you turn the car off (that could be changed, but would need a software change in the car - probably all of them), and when you switch it off, it obviously doesn't do anything because it recognizes it's already off, but when you turn it back to on, it sends another message to turn it on. This allows BMW (and others that use similar techniques) to use less expensive switches, but more importantly, smaller gauge wiring and often much less of it to control numerous functions since the digital messages can easily encode numerous 'states' created by a switch position with only a couple of wires. Since wiring gauge, switch contact capability, and connectors are minimized, it helps save weight and improves reliability and flexibility.

An example (it's different on the i3 for some reason and requires coding to enable in addition to a new switch) on my GT which comes with rear fog lights in the hatch panel, all it takes is changing the switch assembly to the Euro one that has that switch position, and it all works with the new functionality...it's all in the small logic chip in the panel that modifies the message sent, there are no additional wires. It may be that the typical US driver doesn't have the discipline to only use the rear (and front!) fog lights only when actually needed, that they don't offer that in the US, but they're actually in the panel in the rear of both that car and on the i3. The original demo I drove back in 2014 was a Euro version, and it had rear fog light switch. I was surprised when it wasn't' in the one I bought even though the part number on the rear hatch is the same (so has the lights) - they're just not being told to turn on because the computer is not programmed for it even if you change the switch. It annoys me seeing a bunch of people driving with their fog lights on (front or rear) in good weather. At least on the BMW, they tend to be fixed so that they aren't glaring directly into my eyes, but rear ones can be blinding in good weather to those behind and may be the reason why BMW does not include that function on (most?) of their cars sold in the USA.
 
Hi guys,

this is much like in our previous 3-series, where the automatic wipers, switched on with the stalk (aka. the hardware switch, if you like), did not come on after a restart, even when the stalk position indicated ‘automatic’. BMW told us that this is intended behaviour. They said it is to prevent damage to the wipers by activating them automaticaly if, for instance, it might have been freezing in the mean time.

Regards, Steven
 
I think the latter post is correct. Most things don't matter if they are left in the on position and reactivated e.g. Lights etc. Wipers are a different kettle of fish altogether. It can have stopped raining long ago and the window completely dried off or it can have frozen solid or snowed heavily.

Automatic reactivation on starting could cause significant damage to glass, blades or mechanisms in these citcumstances and is undesirable for that reason.
 
Gif said:
I think the latter post is correct. Most things don't matter if they are left in the on position and reactivated e.g. Lights etc. Wipers are a different kettle of fish altogether. It can have stopped raining long ago and the window completely dried off or it can have frozen solid or snowed heavily.

Automatic reactivation on starting could cause significant damage to glass, blades or mechanisms in these circumstances and is undesirable for that reason.
It feels to me that BMW software developers don't make full use of available sensors. Our windshield wipers know when it's raining on the windshield. The car warns about driving in near-freezing conditions. So sensors must be detecting both situations.

Using these sensors, it would seem that BMW software developers could have written logic that would turn on the rear wiper if its switch is on when the car enters Ready state only if rain is detected (i.e., the rear window is wet) and the temperature is above freezing (i.e., the rear wiper blade isn't frozen to the window).

But maybe this isn't a situation that BMW felt was worth dealing with in its software.
 
Gif said:
Didn't think there were any rain sensors at the rear end though? So whilst temperature would work, a dry rear window wouldn't be detected.
I've never read or experienced rain sensors on the rear window, but my assumption is that if it is raining on the windshield, it's likely raining on the rear window :D However, I don't know whether the windshield rain sensor would sense a wet windshield or only rain falling on the windshield.
 
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