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Intermittent wiper does not work


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In my 996 MJ02 the intermittent wiper does not work properly. If I push the indicator stalk down, the wipers move one single 'round'.

In this position the wipers should now be activated every few seconds, depending on the position of the intermittent wiper dial (a potentiometer).

But nothing happens..... the wipers don't move again.

I removed the potentiometer from the dash, unplugged the cable and checked the power supply. It seems that it's properly powered: When I push the indicator stalk down I get 12V between yellow and black. If I turn the lights on I have 12V between yellow and blue. So I think it cannot be the fuse or power supply to this potentiometer.

Now I checked the potentiometer itself with an Ohmmeter. I can connect any combination of the 4 pins but it shows no resistance. But in a poti at least 2 pins should be conncted with a variable resistance....

- Did anybody experience a similar problem?

- I assume the poti is faulty. Is this a common problem?

The poti itself is rather cheap (~20 Euros/25$), but before I buy I new one I'd like to hear for other experiences.

Wolfgang

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In my 996 MJ02 the intermittent wiper does not work properly. If I push the indicator stalk down, the wipers move one single 'round'.

In this position the wipers should now be activated every few seconds, depending on the position of the intermittent wiper dial (a potentiometer).

But nothing happens..... the wipers don't move again.

I removed the potentiometer from the dash, unplugged the cable and checked the power supply. It seems that it's properly powered: When I push the indicator stalk down I get 12V between yellow and black. If I turn the lights on I have 12V between yellow and blue. So I think it cannot be the fuse or power supply to this potentiometer.

Now I checked the potentiometer itself with an Ohmmeter. I can connect any combination of the 4 pins but it shows no resistance. But in a poti at least 2 pins should be conncted with a variable resistance....

- Did anybody experience a similar problem?

- I assume the poti is faulty. Is this a common problem?

The poti itself is rather cheap (~20 Euros/25$), but before I buy I new one I'd like to hear for other experiences.

Wolfgang

Here's some info which may help:

If the potentiometer is open between pins 1 & 2 you would get the exact symptoms you describe. Pin 1 is next to the "little staircase" key/tab side of the connector and mates with YELLOW/RED. Pin 2 mates with BLACK/GREEN. On my'99 996, the pot. measures between pins 1 & 2, approx. 230k ohms when rotated fully C.C.W. and approx. 30k ohms when fully C.W.

I have completely disassembled the rotary control and found it to be quite sturdily built, but I imagine it could go bad, particularly the wiper contact. The laws of probability would seem to suggest that the wiper relay is most likely the culprit, however, if you have carefully measured the pot's. resistance between pins 1 & 2 and it shows open in all positions of the control, that would have to be the problem.

If you have access to some fixed resistors, you could pick a value somewhere within the range I specified above and insert the resistor's leads into pins 1 & 2 of the control's mating female connector. This would allow to verify the relay's operation. Pins 3 & 4 are used only for night illumination. Do you have a fellow 996 owner who would allow you to use his relay for quick troubleshooting?

Edited by Sandy
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Hi Loren and Sandy,

thanks a lot for the hints!

I checked the potentiometer again and (when using the right pins and the right setup of the multimeter :lightbulb: ) it shows exactly the values Sandy had:

30kOhm full CW

230 kOhm full CCW

So it looks like this part works properly.

Next I followed Lorens tip, looked for the relay (pos16), unplugged it and opened it....

Nothing looks obviously wrong... no black spots, nothing looks 'burned', the soldering looks fine....

Is there a seperate fuse for this relay? Can it be tested?

The relay itself is also rather cheap (20€/25$ refering to my price list), so replacing it seems the easiest way to go.

Greeting from Germany

Wolfgang

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Hi Loren and Sandy,

thanks a lot for the hints!

I checked the potentiometer again and (when using the right pins and the right setup of the multimeter  :lightbulb:  ) it shows exactly the values Sandy had:

30kOhm full CW

230 kOhm full CCW

So it looks like this part works properly.

Next I followed Lorens tip, looked for the relay (pos16), unplugged it and opened it....

Nothing looks obviously wrong... no black spots, nothing looks 'burned', the soldering looks fine....

Is there a seperate fuse for this relay? Can it be tested?

The relay itself is also rather cheap (20€/25$ refering to my price list), so replacing it seems the easiest way to go.

Greeting from Germany

Wolfgang

There's no separate fuse for the intermittent mode. It uses the same fuse (C6) utilized for the high and low speed modes.

The weakest link in the relay unit is the mechanical relay inside it. You might take a small screwrdriver and see if the relay's armature moves freely and its contacts aren't welded shut. If the contacts look like they're pitted or show signs of arcing excessively, you may be able to dress them with a tool designed for that job, or a narrow strip of very fine sandpaper. It might restore operation temporarily.

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Hi Sandy,

the relais looks ok on a first glance and like new. The armature moves easily and the contacts aren't pitted. Nothing smoked, blackened, melted....

Do you know whether it can be operated 'manually' ? Could I supply 12V to the pins so that I can check is closing and opening? Should it work with Pin5 (=15) and Pin 7 (=31)?

Well, I'm gonna buy a new one and then we'll see... :o) I must admitt that I am not fully convinced yet that this is the culprit, but I assume I won't find it out otherwise.

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Hi Sandy,

the relais looks ok on a first glance and like new. The armature moves easily and the contacts aren't pitted. Nothing smoked, blackened, melted....

Do you know whether it can be operated 'manually' ? Could I supply 12V to the pins so that I can check is closing and opening? Should it work with Pin5 (=15) and Pin 7 (=31)?

Well, I'm gonna buy a new one and then we'll see... :o)  I must admitt that I am not fully convinced yet that this is the culprit, but I assume I won't find it out otherwise.

Yes, you can bench test the relay, but the hook-up gets a bit difficult because the relay needs to monitor the position of the wiper motor for it to operate normally. The relay normally sees a ground from the motor when the wiper arm is parked and +12v. when the arm is out of the parked position.

I recently bread-boarded the relay on my test bench to run some experiments for determining how to shorten the interval range selected by the rotary control. Consequently, I can give you an idea of what you need to go through to check the relay out.

Pin 1 needs +12v. through a fixed or variable resistor, within the resistance range I previously described. This simulates the potentiometer input from the rotary control.

Pin 2 needs no connection.

Pin 3 is the +12v. output of the relay to the low speed winding of the wiper motor. That winding is used for intermittent and low speed operation. You don't need any connection to this pin to get the relay to operate, just for measurement purposes.

Pin 4 needs a ground to start one intermittent cycle. The ground simulates the wiper parked. If you hold the ground on this pin you will hear one click and release of the relay (the interval being determined by the resistance on pin 1). Removing the ground and reapplying it will give you another single cycle. You need to alternately apply a ground, then +12v., then a ground again, in sync. with the operation of the relay to get a "continuous" sequence of delayed intervals. That is, unless you can actually hook a wiper motor up to the relay, or to a motor with a SPDT switch geared to it, to simulate the limit switch's operation.

Pin 5 needs +12v. (primary power).

Pin 6 needs +12v. to simulate selecting the intermittent mode with the wiper lever arm.

Pin 7 needs a ground.

So, you can see why it would probably be much easier to just try another relay!!!

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  • 3 years later...
Hi Sandy, I think it's really easier to try a new relay then. I'll check this with the dealer tomorrow....

Hi Wolfgang, I have the exact same problem that you described in the opening post. Just curious to know if you ever tried replacing the relay and if that fixed the problem. I know this thread is over 3 years old but I found it on my search and am hoping that somebody can point me to the cure. Thanks.

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Hi Sandy, I think it's really easier to try a new relay then. I'll check this with the dealer tomorrow....

Hi Wolfgang, I have the exact same problem that you described in the opening post. Just curious to know if you ever tried replacing the relay and if that fixed the problem. I know this thread is over 3 years old but I found it on my search and am hoping that somebody can point me to the cure. Thanks.

Me too me too!!! I just bought the car and couldn't figure out why pushing down on the wiper arm gave me one swipe and then it stayed off. I thought there were 2 offs!! :)

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  • 1 month later...
Hi Sandy, I think it's really easier to try a new relay then. I'll check this with the dealer tomorrow....

Hi Wolfgang, I have the exact same problem that you described in the opening post. Just curious to know if you ever tried replacing the relay and if that fixed the problem. I know this thread is over 3 years old but I found it on my search and am hoping that somebody can point me to the cure. Thanks.

Me too me too!!! I just bought the car and couldn't figure out why pushing down on the wiper arm gave me one swipe and then it stayed off. I thought there were 2 offs!! :)

I finally got around to replacing the intermittent wiper relay (position 16) with a brand new relay and still have the same problem. The wiper only wipes once then waits over a minute between wipes. It does not matter if the intermittent wiper interval adjuster knob is set on min. or max. Does anyone know how to fix this problem?

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