Technical Electrical nightmare - screen washer gremlin

[kegless]

Help! I have an X250 ducato and the screen washers stopped working, so armed with the eLearn programme, handbook and a multimeter I set to work on the problem.

Symptoms; When stalk pulled towards wheel the wipers come on for their wash routine (4 wipes followed a few moments later by a final one) but no screen wash.

I know the 'high power' side of the circuit works, if I partially unplug the relay just enough to connect the two large terminals to complete the circuit it works no problem. The relay also works as I swapped it with some of the others of the same type in the fuse box. What confuses me is that the relay receives a 12v supply from both low power circuit terminals, presumably it should only be one. The functional description suggests that the body computer energises the coil by a negative analog signal (I guess it provides an earth?) to the low power side of the system. Does this mean the body computer is not working or could there still be wiring issues (I assume continuity of wiring to the computer due to the 12v on the both terminals of low power side of relay).

Not sure what my next step from here is....I have attached the full wiper electrical system info from elearn in a PDF for your reference. Very frustrating.:bang: Cheers for any help in advance.

 

[rayc]

I am familiar with the circuit after fixing my faulty circuit. mine was just a faulty pump though. The motor has a permanent negative and gets the positive via the relay and fuse in the engine fuse box. If you remove the relay and short out pins 30 and 87 in the holder the pump should run.

In normal use the relay coil gets 12v when the ignition is on from the cab fuse box pin 7 to the relay [B002 in the drawing]. The other side of the relay coil gets a negative to operate it from the body computer [M001 in the drawing] when called for by the stalk position.
It would appear that if you are getting a positive voltage on both sides of the relay coil that it is not getting the negative signal from the body computer.
if it were me I would remove the relay and put the meter across the holder pins 85 & 86 and expect a solid 12v signal when the ignition is ON and the stalk is operated.

It is interesting that you say "if I partially unplug the relay just enough to connect the two large terminals to complete the circuit it works no problem." I do not understand that as what is causing the circuit to complete? Are you sure you do not just have dodgy contacts in the relay holder?

 

[kegless]

Cheers, that is exactly the situation, positive on both 85 and 86 pins as you suggest therefore no potential difference and no current, what I need to know is how to proceed with narrowing down the cause.

 

[rayc]

Well there is only the stalk circuit to the body computer and the body computer itself plus the wiring incidental to the washer circuit.
Are you sure that the relay holder contacts, especially the negative from the body computer on contact 85 are good? If so then you will have to determine if Pin 3 of the body computer is going negative when the stalk is operated.
If not then it could be the stalk itself. [or of course the body computer or wiring].
Your elearn says:
the Body Computer M001 provides a reference earth, from pin 9 of connector B, for the steering column switch unit (pin 4 connector A);
pin 2 of connector A of the steering column switch unit H005 is connected to pin 30 of connector B of the Body Computer M001 which
receives the (negative) analogue signal relating to the operation of the windscreen washer.
As I see it then pin 30 of the body computer has a certain resistance value to negative when the stalk is operated. The resistor is shown in H005.

 

[Anthony489]

Hi Kegless. The fact that the wipers do their "wash routine" implies that there is the corrrect signal going from the stalk to the body computer. You also have the expected +12 volts on pin 86 of Relay T17. So that only really leaves the connection between the Body computer Pin 3 and Relay T17 pin 85, via Pin 6 of connector A on junction unit B001, OR some problem with the Body computer. The Body computer essentially provides a low resistance when current flow is needed through the relay coil for washing. This low resistance is likely to be arranged via a transistor collector so be aware that a simple ohmmeter check of Pin 3 of Connector A of the Body computer to ground with the relay disconnected may not suffice to show a fault. As others have said, carefully check the wiring and connectors, and try to monitor the voltage (relative to ground) directly on Pin 3 of Connector A of the body computer whilst it is still connected to the relay. Anything other than +12 volts which then drops to near zero during washing indicates a fault. To connect a test meter you may need to resort to cutting the relevant wire and re-joining the ends with a screw terminal strip, you can then hold the probe onto the terminal's screw head.

 

[kegless]

Cheers Rayc & Anthony gives me another perspective as head is a bit fried trying to figure it out. Will have another crack tomorrow.

 

[kegless]

The Body computer essentially provides a low resistance when current flow is needed through the relay coil for washing. This low resistance is likely to be arranged via a transistor collector...

Do you mean high resistance? I figured it would be high to give a ground (difference in potential) as both low power pins are positive charged meaning its earth switched. Or am I missing the point

 

[Crossingkeeper]

I am (fortunately!) not familiar with this particular fault but bitter experience of fixing numerous electrical faults has taught me to check the simple things first as it is so tempting with a little knowledge to head for the big expensive and easy fixes.

As Ray says, I would start by providing the washer motor with an independent 12v supply thus proving the motor.

If the motor is ok, I would then check continuity of the 12v supply cable from the relay (using your very useful diagram)

And so on (but I suspect you won't need to go any further than this)

 

[Anthony489]

I'll try and elaborate on how I see the system ought to work.

When the pump is working, pump motor current flows via Fuse F09 in B001, through the closed contacts of Relay T17, through the Washer Pump N020 and to Earth at C010. To close the relay contacts, a smaller current must pass through its coil. This relay coil current flows via Fuse F31 in B002, through the relay coil from relay pin 86 to relay pin 85 and through the body computer Pin 3 on connector A to ground. In this condition there is 12 volts (measured to ground) on the input side of the relay coil, and near zero volts on its output side as the body computer is presenting a low resistance via a conducting transistor.

When the pump is not needed (i.e. most of the time), there is no relay coil current. In this condition there is 12 volts (to ground) on the input side of the relay coil, and 12 volts on its output side as the body computer is presenting a high resistance via a non-conducting transistor.

 

[g8rpi]

<SNIP>
To connect a test meter you may need to resort to cutting the relevant wire and re-joining the ends with a screw terminal strip, you can then hold the probe onto the terminal's screw head.

As an alternative to cutting th wire you can push a dressmakers pin through the insulation and connect to that.

From the fact that it works with the relay partially inserted makes me think it is a faulty relay base/socket or it's connections. As the low side (pin 85) of the relay coil is switched to ground by electronics in the body computer there can be leakage currents that don't affect the relay (a hundred ohm or so coil), but cause strange readings with a digital meter (10 millon ohms). To prevent this use a test lamp (sidelight or interior light bulb) instead of the meter when testing the coil circuit. If you want exact voltage use the meter and lamp together. To rule out the relay base/socket issue, see if you can unclip the relay cover and then plug the "bare" relay into the socket and measure the voltage on the relay itself. Second option is to disconnect the battery and body computer and with the relay plugged in, measure the resitance between the body computer Pin 3 on connector A to battery positive connector. This should read the same (or slightly higher) as the relay coil resistance. If the relay socket is bad, you could just get a relay base and connect it in parallel with the existing socket but tapping into the wiring loom.

Robert G8RPI.

 

[kegless]

Sitting in the van with the laptop now for the wiring diagrams etc. I have managed luckily to back probe the pin 3 of the body computer connector A and was reading 12v with the ignition on, however when the stalk is pulled i didn't get the 0v reading for the reference earth I was expecting from the unit just stayed at a constant 12v.

I guess this means the body computer is at fault as its receiving the signal from the stalk and processing corectly to the wipers but not processing correctly to washer pump. Is this likely to be a new body computer? I'm tempted to put a push to break switch on the wire from pin 3 as a work around...or is there any other avenues to explore?

 

[toyogran]

You have my sympathies!
Trying to fathom out these gremlins take over your life with frustration.
I can't comment authoritively on the X250 platform but can't see it being all different from the X244 system apart from the canbus implementation.
As crossingkeeper wisely points out these problems 99% of the time are down to the simple things in life. My own experience with diagnosing these gremlins is to prove that the components work individually (sounds like you've ticked that box) and then go for the EARTHS/GROUND connections before worrying about system processor bits (black boxes). Because CAN networks don't use good old 0 and 12v values using conventional multimeters can be misleading as many signals are pulse width modulated and need an oscilloscope to reveal what's really happening.
In my experience this black box technology either works or it doesn't and after that it's something mechanical like a connection, corrosion, dodgy fuse or relay terminal. If you can get your hands on a MEGA resistance measurer this will soon check your grounds and get you in the right direction.
Another clue might be in the way the problem presented? Did it just appear or did it develop over time? Spontaneous failure accounts for less than 5% of failures in black box technology.
If all else fails see if anything comes up with a 'OBD' scan then go to the pub.
Good luck let us know what is was!

 

[rayc]

Can you answer the earlier question i.e. "It is interesting that you say "if I partially unplug the relay just enough to connect the two large terminals to complete the circuit it works no problem." I do not understand that as what is causing the circuit to complete? Are you sure you do not just have dodgy contacts in the relay holder?"

How does unseating the relay slightly complete any circuit?

 

[fucato]

FYI
I recently had this problem on my 244 and it was the corrosion off the plug on the pump (which was also the first thing I checked).
Some brushing (with a brass brush) on the contacts and the plug and everything worked again. I also applied some silicon grease, so it can withstand corrosion better.

I also had trouble with some other electrical problems on my ducato in the past and so far it was NEVER in the relay or electronics (but in the plugs, wires).

So I strongly recommend checking the plug at the pump.

 

[rayc]

Can you answer the earlier question i.e. "It is interesting that you say "if I partially unplug the relay just enough to connect the two large terminals to complete the circuit it works no problem." I do not understand that as what is causing the circuit to complete? Are you sure you do not just have dodgy contacts in the relay holder?"

How does unseating the relay slightly complete any circuit?

sorry, I think I have been understanding it wrong. I think you lifted the relay slightly which allowed you to short contacts 30/87 which made the pump run.

 

[Anthony489]

Your test meter result seems to indicate that the body computer or its connector A is at fault. To double check, try disconnecting the wire that goes to Pin 3 of connector A of the Body computer and temporarily connecting it to earth (when the ignition is on etc). My diagram shows the colour of this wire as SV which is Pink and Green. Assuming no other faults this should then energise the relay which in turn will activate the pump.

Assuming it's the Body computer at fault rather than just its connector, there are two permanent ways out of this situation. The first is to pay lots of money to have the body computer changed. The second is to disconnect the wire going to Pin 3 of the Body computer and route it instead to a new Press to MAKE switch installed somewhere convenient. The other side of this switch goes to a convenient earth. This workaround will satisfy the MOT.
I think I know which way I would choose!

 

[adlarplant]

my 2 cents worth if the wipers are working you should be able to assume the body computer is working check the wiring conectors plugs and the washer unit itself maybe its dead as the diagram itself points out the washer unit sends a signal to the body computer not the other way round id replace the pump and go from there Cheers Adam

 

[Anthony489]

The washer unit does not send a signal to the body computer. The eLearn Functional description says: "The Body Computer M001, energises the coil for relay T17, from Pin 3 of Connector A".
It's quite possible for a complex unit like the body computer to be partially working, e.g. 99% OK but one small part faulty.

 

[kegless]

Can you answer the earlier question i.e. "It is interesting that you say "if I partially unplug the relay just enough to connect the two large terminals to complete the circuit it works no problem." I do not understand that as what is causing the circuit to complete? Are you sure you do not just have dodgy contacts in the relay holder?"

How does unseating the relay slightly complete any circuit?

I just used my test probe to connect the two contacts manually.

 

[kegless]

Got other more pressing issues at hand (ducato is a van conversion project) so this one is now on the back burner, will snip the wire from pin 3 and see what happens at some point if it works its a switch me thinks...