I've often see people think their rain sensor doesnt work because they arent testing it properly (normally because they have tested with door open)
a) You put the stalk on the intermediate position (some cars have 2 such positions), but start with the first position
b) If when driving along at a normal speed it wipes at exactly the same intervals then it is either not present or the car thinks it is not present
c) if the intervals are not equal then it is at least basically working
d) It behaves differently when stationary (in that even if wipers are on they switch to intermittent)
e) It does not function if a front door (maybee just drivers door) is open so as not to wet the driver when getting in / out (so you can not test by squirting water on it if door open)
You can thus test it by engine running, doors shut (have window shut also), and squirting water on on it.
What goes wrong sometimes is that the windscreen is replaced and the sensor is not re-calibrate.
The sensor can get 'triggered' when driving through a forest where the light is coming through in 'beams', and iced up windscreens reduce functionality also.
The only way of really diagnosising and of re-calibrating is with Star Diagnosis (sorry)
History:
Cars used to have only 1 intermittent position, and many people found it was not quite to their liking, so MB introduced two positions, one which wipes more often. My 07 ML has the two postion, but an 05 ML I looked at the other day only had 1 position. I prefer the 2nd position (i.e more wiping).
Richard
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