We're getting there.
Remove the 100Ω resistor I see there. As shown on the schematic it's internal to the ECU. The ECU terminals should connect directly to the emitter and collector of the transistor. These points are labelled "+10" and "Hall" on the schematic.
The negative terminal of the cap should connect to the "Hall" terminal too. Can't see from the pic if it does?

 

Yes, the bottom negative its going to hall... But passes thru the 100 ohm resistor. Will remove that.
Other issue now its that the rpm are not stable... It bounces up and down like crazy... From 300 up to 700 and back down to 200... Its there a way to stabilize it? Took it out for a test drive and still shows the sensor error... I believe thats because its not adjusted as it should, and because the signal rpm bounces allot so the ECU gets confused

 

If removing that resistor doesn't do the trick then I think you'll need to wait until you can get a 'scope to see what signal characteristics you actually have, and do some research to find out exactly what sensor signal characteristics your particular ECU is expecting. We're shooting in the dark here. A more complex circuit may well be needed.
A datasheet for the Hall sensor you have would be handy.

 

Couldn't find the sensor datasheet anywhere . It seems im allmost there but not just yet. Removed the 100 ohm resistor, and didn't got any signal after that... So fare the original circuit was the best... Just added two variable resistors on R1 and R2, that seems to allow me more accurate adjustment , but was bouncing allot... if i could somehow stop that bouncing, i believe that's it...

 

if i could somehow stop that bouncing

A characteristic of inductive sensors is that the signal strength increases as the speed increases. The simple circuit doesn't compensate for that, so some pulses may not be detected. A more complex circuit could provide amplification, gain control etc to compensate, and give squarer pulses to the ECU.
Interference may be a cause of some of the 'bouncing'. To help overcome that you could try connecting a capacitor (about 100 nanoFarads might work) between the base and the emitter of the transistor. Also, the wires from the sensor to the circuit ideally should be a twisted pair; as should the wires from the circuit to the ECU.

Edit:
Do you have the car's wiring diagram, or at least the part showing the connection of the sensor to the ECU? Might give us a clue.

 

I got it done 100% !
I wish i could explain it in a more advance way, but even so, i hope it will make sense for you.
So... ive used your last circuit Alec_t , but ive made small modifications ...
First of all, i have inverted the sensor wires going to the circuit... Ground to power and power to ground.
Then, ive took the ground (which was the power + before) and i connected it directly to the ground that comes from ECU. I have soldered them together and to the ground (bottom right in the picture posted early'er), and that did the trick...
All bouncing disappeared , and the rpm stays firmly around 700 rpm... yesterday i have sayd the rpm should be around 500-600. I was wrong.

As ive say'd, i wish i could explain it more detailed , but hope you get me....
I really wish to thank you all for your contribution, but especially to Alec_t and crutschow for having so much patience with me
I will report back within a week or so, to confirm whether it work well or not...
Tested yesterday around 2 hours, and had no error anymore

Thank you so so much !

 

Well, I haven't quite followed how you now have it set up but hey, if it works it works! That's good news. Since auto is a harsh environment, make sure that you anchor the wiring to the circuit board mechanically to prevent trouble from vibration. Also consider lacquering the whole thing to keep moisture at bay. The board should be housed in a suitable project box for protection.

 

I'm really sorry, but dont have the right software in order to draw the circuit as it should, but ive made a little paint modification of your circuit, hoping it will be more clear what changes ive made...

Also, ive play'd a little bit with the two variable resistors, so i should read the new values just in case... and make a note off course

 

Hello!
I'm reviving this thread, because i keep having issues with the car... every now and then its going into limp mode. Ive checked the sensor live readings , and it seems that its bouncing allot... meanwhile, checked on another exact same car, and the sensor readings should be a constant 768 rpm on car idle... on my car its bouncing no matter how much i try to adjust the variable resistance ...

If anybody has an ideea about how could i stabilize the sensor readings, i woulr really apreciate it

 

See posts #43 and #45. I think you need a more complex circuit.

 

Hi! Thank you for remembering about this old thread

I remember you have sayd that some posts behind... but could you please help me with that complex circuit? or at least having an ideea what that circuit involves? Everybody teels me to simply quit on it... But i cant... i saw it working once, so i know it can get better and find an solution to that annoyng error and the limp mode that follows...

Thank you very much in advance! And thank you for the patience you had since the start!

 

Do you now have the 'scope? If so, connect the probe and ground clip to the sensor to check the sensor waveform at idle speed and post a pic.

Edit: I see on an Audi forum that the Audi A6 has a G28 engine speed sensor (ESS). That is a 3-pin Hall device. What code does the original ESS on your car have? Can you confirm that the ECU connector socket on your car is intended to receive a 2-pin plug and not a 3-pin one?

 

Yes. After taking the gearbox appart, im pretty shore the sensor only has two (2) wires. And the sensor name is G182 imput speed sensor.
I have that cheap scope, but cant relay on him , so just to eliminate any possible mistake, will need to use a better one... Will try to have a friend have a look with a more accurate scope. Will post back the results.
In the meanwhile will try to add that 100 nano Farads capacitor betwin the base and the emitter of the transistor
Will report back the result... Hopefully will be able to do that today.

 

im pretty shore the sensor only has two (2) wires.

Yes, but what about the ECU socket?

And the sensor name is G182 imput speed sensor.

Is that the marking on your new sensor or the original one?

 

The original sensor name is G182. The sensors are named the same both... The difference betwin them its that one is hall and the other is inductive... Audi decided to change the sensors types from one year to another. But they keep the same exact name for both

The ECU or TCU, (transmission control unit) wich in our case its the one that receives the sensor readings, it only has two wires comming from the sensor, ive checked all the wiring starting from the gearbox allway up to the TCU unit, and also checked with schematics wich in this case ive been able to find... The wires are white and brown...

I have just tryed to add the 100 nano f capacitor, and doesnt seem to make any change... Signal still bounces betwin 650 up to 850-900

 

The ECU or TCU, (transmission control unit) wich in our case its the one that receives the sensor readings, it only has two wires coming from the sensor, ive checked all the wiring starting from the gearbox allway up to the TCU unit, and also checked with schematics wich in this case ive been able to find... The wires are white and brown.

What is the voltage, measured with your DMM on a suitable DC voltage setting, between the brown wire and ground?

 

Hi! Ive been very busy lately, and didnt work on this project anymore. Last week ive did a big descovery... I was looking at those cables going into the transmission central unit, or gearbox ECU, and found out that you was right about the third cable...
Yes indeed i have a third black cable thats comming from the sensor and going into the ECU...!
I cant understand how could i miss it all this time and after checking everything many many times...
So yes... I have 3 wires... Brown,white and black.

I guess this does change everything right?
Unfortunatelly i have some exams comming soon, so wont be able to do any work arround cars, but if you have any sugestion will be more than happy to lisent to it, and if possible try it out some weekend

 

I guess this does change everything right?

Indeed it does. It means we've wasted our time barking up the wrong tree from post #1 . So in all probability you have a Hall sensor but it's defective.

 

So you say that there is no chance to do anything from the exterior? And that the only chance its to open the gearbox again and swap the sensor for a new one? Damn thing ... I never seen that black cable there... Ok, but if they are both hall sensors, (the one in the first gearbox and the other from the second) why are they different shapes and locations? As you can see on first page where ive posted some images of the sensors... Im a bit confused... I wish i could find some datasheet or some extra info on this sensors.

 

Ok, but if they are both hall sensors, (the one in the first gearbox and the other from the second) why are they different shapes and locations?

It's common for manufacturers to move/change components on different models or in different manufacturing years if, for example, a cheaper or more reliable component/manufacturing process becomes available.
Before condemning the sensor it would be advisable (if you haven't already done so) to thoroughly check the connecting wiring and plugs/sockets. Vibration, corrosion and oil seepage can play havoc with those. Cables may look alright but have internal wire fractures. Connectors may look alright but have loose/corroded wire crimps or oily contacts.