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windscreen washer problem


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Really confusing problem as to why windscreen washer wont work.

On fiesta washer Pump works one direction to wash windscreen and other direction to wash rear window by the BCM sending 12 volts +ve or -ve to pump  . I have removed pump and it works fine in both directions. I have checked at the pump connector that as the stalk is either pulled to wash windscreen or pushed to wash back window i get either 12 volts positive or negative , indicating that the switch is correctly signalling the BCM to provide the voltage as it should. However when i put the connector back on to the pump the pump only operates the back washer , and the pump makes no noise, when trying to wash the windscreen.

I am at a loss as there are only 2 connecting wires to the pump, so in order for the back washer to function as it does there must be some continuity via connector and wiring, so how is it that when 12 volts is effectively reversed but using the same 2 wires , the pump makes no attempt to function. Remove the connector and connect battery direct both washers work depending where i place +ve and -ve connections.

Anyone out there with good Auto  electrical understanding to explain what might be happening. ?

We thinking would be a short to earth when under load at connector or wiring loom but if that were the case neither washer function would work. Hence my total confusion

(BTW i did break one of the wires going into the  connector by accident and had to repair it , but this problem existed before i touched it and still exists since i repaired it so i don't think this is relevant)

 

 

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are you sure there isn't a blockage in the windscreen wash hose or squirters, if the pump expereinces too much resistance it won't pump the washing fluid in that direction

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Hi, Russ. I do like a challenge 🤪 not the problem, just how I'm going to explain it !! Well firstly you seem to have done an excellent job in working out how the pump works and also I guess you tested it by just connecting it directly to a 12V battery first one way round and then the other. So it is safe to assume the pump works fine. You have also tested the signal from your switches to the BCM. So far so good.

Now if I understand you correctly when you operate the washer switch in one direction you get a positive 12V signal with respect to the chassis ground (Negative). But when you operate the washer switch in the other direction you get a Negative signal with respect to the battery positive terminal. Do I understand you correctly ?

The reason I'm just trying to confirm this is because as far as I know the BCM requires a 12V positive signal from both the front screen screen switch and also from the rear screen switch. The signal from each switch is sent to the BCM and depending on the switch operrated the BCM will then send power out to the pump either Pos/Neg -OR- Neg/Pos depending on the signal received. Inside the BCM is a transtistor switching array, think of it as an electronic relay with two change over cotacts and two coils (in real life remember this electronic). If one coil of the relay was on the the contacts would move in one direction and send out a Pos/Neg supply, if the other coil was on then the contacts would move in the other direction and send out a Neg/Pos supply.

So either you have a faulty signal from your washer control switch, or you have a faulty BCM, or I have not understood  you correctly.

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The switch controls the power to the pump, not the BCM

In the switches rest position it supplies 12v to both wires connected to the pump.
When either the front or rear wash is selected, it removes one of the 12v and supplies a ground instead.

The BCM detects which wire has been grounded and turns on the relevant wiper motor.

Does the front wiper operate when the front wash is selected?

washer.thumb.jpg.43e147764fa381ae2a4554ae208d3cf7.jpg

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H Dan62, very helpful schematic. Just had a look at it was just woundering is "6" 2081 the ground connection ?

 

 

 

Washer switches.JPG

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1 hour ago, unofix said:

H Dan62, very helpful schematic. Just had a look at it was just woundering is "6" 2081 the ground connection ?

 

 

 

Washer switches.JPG

Yes, when I did the screenshot it missed the full ground connection.
That was the best schematic I could find that showed the switches, its accuracy regarding fuse or pin numbers are probably inaccurate. But it does show the 12v going to pin 1 and through the normally closed switch contacts. And as you have pointed out the ground on the normally open contacts.

This type of switch and motor arrangement has been used on Ford's for many years, cheap and simple.

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Hi Dan62, thanks for confirming that. I note what you say about the pin numbers might not be correct but just for the sake of this lets just assume they are correct. So if the guy with the problem 'Russ12345' was to disconnect (remove from the connector) wire "2"C2081 and connect it direct to ground then the screen wash pump should operate for the front screen. Also if he was do to the same with wire "7"C2081 (But of course not at the same time), then he could expect the pump to operate in the reverse direction and the rear screen wash to work. If both tests work he could probably just have a faulty switch, but if the pump will still not run for the front screen then the problem is more likely that the BCM  is at fault. Do you agree ?

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sorry guys i have had a pc problem to prevent me getting back on here. thanks for the suggestions so far.

Dan62 , your explanation fits in with my findings (and yes the wiper motor operates with a couple of wipes when i operate the front washer switch). The issues is i can disconnect the connector to the pump and monitor the 2 wires at the connector and can see, as each washer switch is operated one of the wires moves to ground to give me 12 volts +ve or -Ve at the connector . only when i reconnect to the pump, operating the front screen switch does not result in pump operating no noise at all. Back works fine. can switch washer pipes around to prove no blockage in pipes.

Hence my confusion, if i can see each wire going to ground when connector is off of pump, and i can prove the pump is fine both directions when connected to battery direct, then it would point to a short somewhere under load , however if this was the case i should expect when i connected it to the pump not to work in either direction.

Could it somehow short out in one direction and not the other ? could the connector be slightly faulty, making a poor connection that somehow operates the pump when flowing in one direction but not the other ?

My knowledge of electronics at this level is weak. 

Thoughts 

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  • 2 weeks later...

just hoping that either unofi of Dan62 may see my last post and give an opinion. you have both been so helpful ,but really keen for you final thoughts on the subject any chance?

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Hi Russ, you do have an interesting problem, so a bit more testing and fault finding is required. I assume that you are able to get to the connector that goes on to the screen wash pump. Get yourself a regular 12Volt 21Watt bulb as it makes an ideal load and fix a couple of wires on to it (solder would be best or an old lamp holder). Pull the plug off the screen wash pump and then push the wires on the bulb in to the plug. Make sure you have a good contact.

Now operate the front screen was the bulb should light nice and bright. Next operate the rear screen wash again the bulb should light nice and bright. If both those tests are fine then it would seem the pump is faulty. If as I suspect the bulb will only light when rear washer is operated then we are looking at a BCM problem.

Get back to me and let me know what happened

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Hiya russ, ive just joined the site. I had the same problem.

My washer at the front stopped working. I couldn't hear the motor working when i operated the washer switch. But when i lifted the bonnet it started washing.

I found out that as the bonnet lid shut it trapped the washer pipe. as there was no flow it wasn't working.

I moved the pipe and fitted a tie wrap and has been no problem at all since.

This may sound so stupid but it did work for me.

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Thanks half price but as i have said i have swapped the pipes at the motor so now the front washers work when i push back washer switch which illuminates any issues with pipes. I like the idea mentioned by unofix however to get the wires from a bulb to make a good connection inside the connector is very difficult. 

 

I think i will need to bite the bullet and cut connector off and put terminal block in series  to allow me to try the bulb idea or/and  possibly a new connector. 

It cant be the pump as i can connect a battery straight to it and it works perfectly in both directions.

Just in summary i have 12V at each of the 2 wires connected to the pump at rest as it should be. Operating the front washer or rear washer switch, correctly sends one of the wires to ground (checked by my volt meter with connector removed from pump)providing a circuit for the pump, and the appropriate windscreen wiper wipes, which indicates to me BCM has recognised switch movement and correctly passed on its signals. But once put connector back on pump , only back washer pumps . Front wiper wipes but no noise at pump for front washer. 

All this points to a circuit leak/short under load between BCM and pump, most likely place being connector, but the bit i just cant understand hence my plea for help to any of you with good auto electrics knowledge , is why does the pump work at all ? if there is a short under load and the pump only has 2 wires going to it why under load does it continue to perform correctly when pos and neg are applied in one direction and yet refuses to operate when the polarity is reversed ? if their was a short/leak surely it would not work under load regardless of polarity ?

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Hi Russ, chin up, your nearly there 😀. My thoughts are if you disconnect the pump and just use a 12V 21W bulb (we can call it an Optical Motor) you will be able to see if it lights in both directions. You need to do the test with the pump disconnected.

When you used your meter to measure the 12V positive with respect to ground (0V) did you have the pump connected ? If you did then you would get 12 volts on either wire even if one of them was open circuit, since the resistance of the pump motor is low the voltage from the working wire would back feed via the motor and show up on the other wire as well.

When you do get to the pump and disconnect the plug, measure the resistance of each motor terminal on the pump with respect to chassis ground. Both terminals should be open circuit to chassis.

Let me know how you get on

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so been out again today and rigged up a bulb to provide load - disconnected from pump but added volt meter to check voltage if light did not work.

following tests.

ignition on - checked at rest i have 12 volts on both wires as i believe is correct. operate rear or front washer switch monitoring both wires and as switch is operated i get 12 volts in one direction and then 12 volts in the other, as i would expect.

Add in the bulb.

operate rear washer switch - bulb lights up - meter reads 12 Volts. Rear wiper wipes a couple of times correctly.

operate front washer switch bulb does not light and meter reads 0.5Volts - front wipers also wipe as they should.

This i thinks proves as suspected that somewhere there is a short/leak under load in one direction only which i still don't understand how is possible. Tomorrow i tend to remove connector and fix bulb directly to wires to eliminate a connector fault , but after that i am at a loss again. 

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Hi Russ, well you have proved the issue is not the pump and is looking more like the BCM, or more likely a correded wire / connector. What looks like is happening is the 12 volt positive supply is dying underload. There is a known problem with water ingress in to the BCM plug that affects quite a cross section of Ford vehicles. The connector on the screen wash pump gets wet due to a small leak in the actual pump. The water travelles along the wires by capallary action and makes its way back to the connector on the BCM.

Remember the screen wash switches are sending a signal to the BCM which removes the positive from one wire and connects it to negative. Its time to get stuck in to the BCM and have a very close inspection of the plugs, wires and crimp terminals

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thanks UNOFix - very frustrating to know its a common problem at BCM plug . but makes sense what you are saying , and i see what you say about one wire not correctly being made to ground but could still carry positive voltage when driving the other way.

Given you extensive knowledge could it be as simple as BCM plug needs drying or is it likely to have caused a problem in BCM itself. ?

At this point do you think it could be the connector on to the pump as i would prefer not to cut connector off just to eliminate bad wire to connector problem as if not that then i will have to reconnect it ? 

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Hi Russ all the information I have seen so far it has always been the connector at the BCM and oddly not the connector at the pump. I think the connector you need to check is the bigest one on the BCM, possibly with a green cover (Not sure)

I think a company called SY Diagnostics have a You Tube video of the finding the fault on a 2014 Mondeo.

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I have found and watched the video and can certainly look at the connectors to see if any evidence of water ingress. The pump and connector look ok unlike there pump in the video where you could see water on the connector.

so i re read what DAn62 had said about the switch providing the current straight to the pump and the switch itself provides the ground, and signals the BCM to operate the wipers. Given the wipers are operating could it be a fault in the push in switch not making a good ground connection and nothing to do with BCM ?

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Hi Russ, I take your point - - - but it looks like you are loosing the 12V Positive. So it seems that the switch is doing its job of removing the 12V positive from one wire and connecting it to negative 0V. The problem seems to be that the other wire which should remain at 12V Positive is dying when under load, probably due to high resistance somewhere in the system.

Are you able to get to the two wires on the switches for the front and back screen wash? If yes then we can do a little test.

Keep me posted please

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Thanks to you both for all your help. I put back connector on pump , checked all BCM connectors for signs of water ingress , found nothing looked totally healthy. Had given up thinking it might have to go to garage, played with the push button several more times and the on tenth push water started to spray , and has been working ever since. I have obviously pushed this many times before with no sucsess.

so no real idea why its suddenly working but i think it now firmly points to bad push switch on stalk as suggested .

thanks again for all the help, if goes again i will invest in new stalk, before any further investigation

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