I understand these beasts have rain sensing wipers, but my 2002 XJR lets me know when I go over a bump in the road by doing a single wiper wipe. Any thoughts as to where to start looking? I have tried to recreate this by tapping what might be the obvious locations.

• Run/stop & fast slow relays (I have not swapped them though)
• Wiper motor park switch
• Stalk switch

The wipers work normally, slow, fast, intermittent (timed) but certain road bumps, and not big ones will trigger a single wipe.

 

The solution is to turn the wipers OFF when no rain is forcast.

I have gone round-and-round with customers and Jaguar Tech Line back when the Auto Wipe system first came out and the final outcome was that there was nothing I could do to stop the occasional single swipe caused by a large BUMP.

I asked about adjusting the sensitivity (no adjustment)

I tried new windscreen sensor, new sensor module etc.
Nothing changed!!!!!

If you do find the answer, please post back.

bob gauff

 

Thanks Bob,
At least I am not alone in seeing it.
My plan of approach then is seeing if I can somewhat reliably reproduce it, and then remove items to ensure that it is not that component that causes it.
I am suspecting that it could even be high frequency vibrations on the window and sensor make it overly sensitive.
I wonder if it is like this TRW system.
http://static.howstuffworks.com/pdf/rain-sensor.pdf

Eliminate:
Unplug the rain sensor
Unplug connection to stalk
Unplug start stop relay
unmount but leave plugged in relay
And validate if it stops, or still continues.
At least to try and isolate and find out what component is the trigger for it.
I presume it worked right once during design....maybe

Dave.

 

Mine does the same, it is also effected by certain types of shadows. I just turn it to off when it doesn't rain, it really isn't too much trouble to do that.

If I hit the sensor unit from inside the car it normally sets it off also if you're looking for a way.
S.

 

i found that it got much better when i tightened my rear view mirror...it was loose and shook every now and then which set off the auto wipers...

 

I have the same problem with my '03 XJR and I just turn them off if I don't need them. I have had the sensor replaced and it did not help. My mechanic at the dealer told me that they see this a lot and their solution is to just turn them off. He hinted that it may be a design flaw and that it is not worth the time and money to try to track down the source or replace a bunch of parts.

 

Well, after having some rain and experience the convenience of the rain sensing but the frustration of the bump sensitivity/vibrations I diagnosed further and I think I have solved my issue. I have since driven over expernansion joints, rail road crossings and pot holes, all past triggers. Oh, it still senses rain too.

For me I did validate that the sensor was the trigger for the sweep, by unplugging it. It then did not sense rain as expected and did not bump activate. As a previous poster said, if the cover around the sensor was loose enough to touch the sensor, it could be triggered.

What I found made the difference was the quality of the gel pad and its application to the windshield. It seems that an IR pattern is set up from 8-10 emitters in the sensor circumference radiating out through the glass and a reference is established to a detector in the center. A poor seal or gaps or air pockets cause substantial interference and cause the trigger.
Looking at my sensor, it looked like it was attached, firmly enough it seemed, but it looked as there were some 'wrinkles' in the seal. I did not know at the time that it would have much of an issue, but I suspect that maybe it had been reattached or the windscreen replaced. Some European sites seem to indicate that it is an issue for some makes, and ebay UK has "rain sensor Gel pads"

I pulled the sensor off, and 'rolled' the tacky pad off. Checking the intermittent at this point makes it seem t be almost continuous, any touch or movement would set it off. The gel pad seemed to be like those silicon anti-slip cell phone pads ~1/16" or so thick. I found some 3M-Scotch light duty 'reusable' lite duty mounting tape that came in 1"x1"x qty 3 squares taht were 'about' the right thickness. Using one tab, I cut the corners of and made it a 1" circle.

Cleaning off the sensor surface and the wind screen, I applied the tab to the sensor and the sensor to the glass, centered in the black opening and ensured no air bubbles remained. Now driving through any of my past trigger points does not set off a wipe, but spraying the window with water will still cause a wipe.

While the sensor is off, or even while still attached, you can check that the IR emitters are IR emitting by pointing a digital camera at the sensor in the windscreen with the ignition on and the wipers on auto. They should all show as illuminated blue/purple LED's in the screen of the digital camera. If this is working and you think the sensor is otherwise OK, you may want to check the quality of the attachment to the screen.

So far, I would pass it.

 

Yep.

This is the key phrase from the linked pdf above:

When the device flops around, the reflected IR changes and away you go.

 

dsetter, thank you, I am having the same issue and did not realize that you can remove the original goo and remount it, that is awesome! Right now the slightest touch to the sensor (or the plastic mirror-shell over it) sets off a wipe.

Could you please provide a URL to buy or a photo of the 3M-Scotch light duty 'reusable' lite duty mounting tape that worked for you? Thanks!

 

Here is an image of it.

Scotch Cat# R100.


Been out raining here a bunch and it is working fine for me now.
The old 'goo' piece came off quite easy as one piece. you can use that as a template to cut the other. I actually used one on the 1"" squares that is just a touch smaller.
After cutting the piece to size, each side has a protective adhesive cover.
Remove and place on the windscreen 1st to get it centered in the clear area.
Check from the outside that you do not have any air bubbles in place.

Then remove the other protective cover and place the sensor.
I think it helps if you apply it at an angle so the air is less likely to get caught.

Hope this works for you too.