G68 - Vehicle Speed Sensor Info please

[S2central.net]

G22 / G68 notation is interchangeable on the Audi diagrams. I cannot remember exactly when or why the notation changed.

[S2central.net]

I would need to dig out some old posts and notes about this but my memory is that you can wire G68 directly into ecu. The production of the VSS signal at the speedo is more about buffering the signal so it can be presented to many controllers eg ecu , tcu, abs, radio/gala, cruise control, difflock - I think that's them all for a B3/B4.

In saying all that - I could be talking from flawed memory here.

[edge_devil]

Thanks Paul. I have cleared the fault code so I may be okay now.....I will check later this week/at the weekend.

Is there a scientific way to check it is working correctly like driving in gear and taking your foot off the throttle and letting the car roll out in gear ?

[edge_devil]

Look on page 2 of this post. I did some testing personally on my Urs4 with my multimeter. Use the later posts, I had to correct some errors and did not have editing privileges at the time. I believe I was measuring the output of the gauge cluster, at the red connector in connector station 2. I tried putting my meter on the actual device on my spare tranny and did not get any output, but I could have been measuring incorrectly at the time (i think voltage instead of ohms) assuming it was a hall sender vs a reed switch.
http://forums.audiworld.com/showthread.php?t=2834884

Cool thanks, my library of information is building, hopefully I will be up and running soon!!

[S2central.net]

Best way to see if VSS is working is with vagcom / vcds while running - there is a measuring block which shows VSS in kph. Cannot remember which block but is easy to spot it.

[edge_devil]

Voila!

Not sure why it was showing 4.0... car was staionary!

[S2central.net]

Ahh this makes me think that G22 is the reed switch while G68 is the Hall effect... It might be the root cause of some bizarre behaviour I had on a local UR conversion to ABY with an 016 gearbox. A pull up resistor could be all that is needed for a fix.

[S2central.net]

Voila!

Not sure why it was showing 4.0... car was staionary!

That is the normal behaviour. Very non-German but there you are !

[dustovich]

Its not like your speedometer can display that low of a speed anyways.

[S2central.net]

Well indeed , but you would just think that no signal would be translated to 0kph instead of four - there will be some logic and rounding in the ecu which produces a result of 4 from no-signal.

[dustovich]

I know from slight tinkering with my arduino in trying to use the gala signal to measure speed/total mileage that when the speed is low the accuracy would not be very good. Especially if you have no pulses during the loop. If the wheel rotation resolution would be higher the accuracy at low speeds would be a lot better ie 16 pulses/rotation. But I see your point with the no speed. That is probably why the speedometer doesnt show speeds below 10-20kph, not enough samples.

[edge_devil]

Oh and btw....

I should just be clear that I am using the original 1989 5 speed, 2WD AMK gearbox...which has the G22 2 pin sensor.

I'm busy for the next few days and it's a bit late to fire her up, but I should know by the weekend. I'll let you know how I get on.

Thx for the input y'all

[edge_devil]

All cleared up .. .for me at least

I've just run the engine up with the back jacked up (That's where the engine is and then ran through a few gears with VCDS-Lite connected. Speed is shown and it changes so YES you can connect directly from G22 and it looks to work fine!

[S2central.net]

Good-oh - my memory isn't completely shot then !

[Thuppu]

Question about the GALA speed signal? Is it a digital signal I can hook up to my ECU? Page 31. http://www.maxxtuning.eu/documentati...andbook-eu.pdf

According to this, it should be acting like a digital 0-5V pulse signal... http://www.s2forum.com/forum/showthr...&highlight=vss