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D3 - Axles, Brakes, Suspension and Steering Brakes, Springs, shocks, steering racks, steering columns, suspension arms, wheel hubs etc.

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  #21  
Old 10th July 2019, 12:17 PM
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Originally Posted by steamship View Post
Maybe someone who can read current flow diagrams can assist. Here is the relevant diagram, and from it I can see that the two heavier wires go to the actual motor. Not sure about the other two.
There's not really any info there to read, except that the symbols imply that there is some electronics involved. The ECU terminals are marked S+/S- (as opposed to the M+/M- of the motor terminals), so my guess is 'S' stands for signal and that they provide some sort of feedback. It could be a serial data link (probably unlikely), PWM (possible) or a simple 0-5 volts signal. I'd start by putting a (DC) voltmeter across the wires to see how it changes. If that's inconclusive an oscilloscope should reveal what's going on.

The fact that there are only 2 'signal' wires would lead me to suspect that it's just a simple voltage/resistance measurement, anything more sophisticated would require a power connection too. While it's possible to send power and data over the same wire, I think it's rare to see that in automotive applications.
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Last edited by moltuae; 10th July 2019 at 12:35 PM.
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  #22  
Old 10th July 2019, 12:43 PM
HPsauce HPsauce is online now
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That other symbol is for a transistor. Probably part of the control mechanism for end of movement in some way?
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  #23  
Old 10th July 2019, 01:55 PM
paulrstaylor paulrstaylor is offline
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I'm sure this was discussed previously, possibly on another forum, but I know I had similar thoughts when I had a D3 (5 years ago)....

From memory, the A8 had a hall sensor in the motor, that the passat does not.

The motor is driven by a big transistor in the control unit (one per side) that had a tendency to burn out (or end up with a dry joint).

On my car, I replaced one caliper (refurb from ECP) which was gummed up, a month or so later the other failed with the same issue so that got swapped also, but I couldn't get the fault to clear which was resolved by buying a brand new control unit - total cost at the time was ~700....

if you want to use the passat motor, you may also need to look at the passat control unit, but that then leads to questions about broader integration, so was in my view at the time more hassle than it was worth.
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  #24  
Old 10th July 2019, 02:11 PM
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Quote:
Originally Posted by HPsauce View Post
That other symbol is for a transistor. Probably part of the control mechanism for end of movement in some way?
I think the transistor symbol is generally used these days to symbolise any type of electronic device/circuit rather than a single bipolar transistor, like it used to do (back in the days of single transistor ignition coil amplifiers, for example). The J540 ECU in the diagram has the same transistor symbol but no doubt contains numerous components and several integrated circuits.
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Old 10th July 2019, 03:42 PM
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I think the other wires are to do with determining pad thickness(wear).
When I stripped my calliper down to refurbish, I didn't see any other way that the car can determine pad thickness other than how far the motor mechanism moves in relation to the pad thickness that you are supposed to program in via vcds on installing the new pads.
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Last edited by ivanhoe; 10th July 2019 at 03:56 PM.
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  #26  
Old 10th July 2019, 07:42 PM
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The two thin wires are to count the revolutions of the motor and so calculate the change in pad thickness (wear) there is a hall sensor in the motor housing and these wires connect to that, it gives a small 'blip' signal when a magnet passes by. (A bit like ABS wheel speed sensor I presume).

As it was not very reliable, they went back to wear sensors in the pads on other models.

There is a thought that the A6 EPB module is the same except for ignoring this wear input, therefore may be more reliable and you can just rely on your eyes for the pad wear.
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  #27  
Old 12th July 2019, 06:30 AM
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Hi Snapdragon

Does that mean then that it could be entirely possible to still use such a motor and simply hack the connector such that the additional two wires are not used?

If so, then like you suggested, the pad wear could be left to just eyes only?
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  #28  
Old 12th July 2019, 01:58 PM
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Someone was going to try it but if they did I missed the results - not aware of anyone trying it - so it is just a theory.
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  #29  
Old 12th July 2019, 02:53 PM
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Quote:
Originally Posted by snapdragon View Post
Someone was going to try it but if they did I missed the results - not aware of anyone trying it - so it is just a theory.
It was definitely discussed here previously on the forum as a possible solution, and may have been paulrstaylor as he mentioned above.
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  #30  
Old 12th July 2019, 03:00 PM
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Sounds like it would be quite straightforward to make an emulator (powered by the motor wires), generating the required sensing signal while the motor runs. Might take a bit of research and testing though.
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