VW electronic speedo sender questions.

[truckinwagen]

I have a few questions about the VW electronic speedo sensors for 020 transmissions(found in MK3's I think)

I have one for my electronic speedo, but am having some issues getting everything to work right.
I assume that the terminals marked + and - get hooked up to switched power, and ground.
which leaves the middle terminal marked "A" as a signal wire to go to the gauge right?

anyone know how many pulses it generates for every rotation of the tires?
what kind of signal does it generate? similar to a magnetic proximity sensor?

my speedo died yesterday, so I am trying to get the electric one working as fast as I can.

-Owen

[truckinwagen]

ok, so a little research shows that the sender should put out four hall pulses per wheel revolution.

how does one test for the hall pulse(to make sure it is working right) with simple tools?
I hooked up a test light to the sensor wire, and drove around, and nothing.
but I suppose the hall pulse could be too weak to light the test light, so it does not really mean much.

I need some way of figuring out if it is the sender, or the gauge that is bad, because supposedly the sender generates a hall pulse, and the gauge is driven by a hall pulse.

help would be great!

-Owen

[the caveman]

The best way to check would be with a voltmeter with a dwell/hz  function. You can then see not only the voltage but the signal. I have been confused in the past with only checking voltage.

[truckinwagen]

I might see about getting a new multimeter with a hz function, my old one took a dump, leaving me with nothing but a test light.

how much voltage should be expected from a hall sender?

[Vincent Waldon]

It will be either 5 or 12 V... if you don't have a Hz function you should still be able to discern the individual pulses at the output as you rotate the sensor, but you need to use a voltmeter at a minimum rather than a test light, as a testlight might draw too much current and damage the sensor.

[truckinwagen]

thanks, I'll do that.

[truckinwagen]

I got myself a new muti-meter.
no HZ function, but it was cheap(and I'm broke)

so would the pulse show up as a varying DC current or an AC current?

[macka]

shoul be vdc

[truckinwagen]

well, playing with my multimeter and the sender, I cant get any kind of pulse out of it.

and with a hall sender(that I have confirmed works with my multimeter) I cant get the speedo to do anything.

so the only conclusion I can draw currently is that both the sender and the speedo are bad.
gonna just run without a speedometer for a while until I can afford a Trailtech Vapor.

with the vapor, I should be able to get speed(from a magnet attached to one of the CV joints for pulse) and tach(with a magnet attached to the crank pulley for a pulse)

it will also read water temp, with a programmable warning light output that could be used to control radiator fans or the like.

should be about $200 shipped(should be less, but they only ship UPS <GRRRR...>)

but for now, I will just drive with the flow of traffic.

-Owen

[Vincent Waldon]

so would the pulse show up as a varying DC current or an AC current?

Neither.   You should see a DC voltage.. in a repeating pattern as you slowly turn the sensor:

0V  -> 12V  -> 0V  -> 12V   etc etc. 

The cluster is expecting this voltage train, so probably won't respond to a raw Hall Effect transducer.  I say "probably" based on my understanding that the Vss transducer does a bit of signal processing.. but I've not measured one directly, so could be full of you-know-what. 

[truckinwagen]

well, I got nothing out of the sender at all.

the only reading I could get at all(which was not changed by rotating it) was 5 ohms resistance between the pos and neg terminals on the sender.

the speedo is supposed to respond to a hall pulse, and when I used my hall sender(pulse when a piece of metal is passed by it) the speedo did nothing.

I am going to stop worrying about it, and focus my attention on other things that are more important liek motor mounts and exhaust.

-Owen