G68 - Vehicle Speed Sensor Info please

[dustovich]

The largest differences between the Reed and the hall would be that the hall needs to be powered to work and that it doesn't require a magnet to work.

[johne]

The largest differences between the Reed and the hall would be that the hall needs to be powered to work and that it doesn't require a magnet to work.

Both the reed switch sensor and the Hall sensor need a magnet to work.

Both need power to work as well since if the reed switch isn't being used to switch power on and off you can't tell if it's doing anything.

John

[dustovich]

It is all in the way is is described I guess. The Reed switch is a 'dry contact' and will operate without a separate supply voltage powering the sensor itself. To read the open/closed position you do need electricity though. A hall sender does require supply voltage (thus is why it requires 3 wires to function vs the 2 wires of the Reed switch).
You are correct that hall senders do require a magnet, but in our car's application those magnets are built into the sensors themselves. The flywheel and cam pulleys aren't magnetic, they just interfere or modify the pre existing magnetic field.

[terrybullwon]

Dash I have here, T26 connector pin 8 G22 signal in is a earth wire brown not as per the suggested data Dave?

[S2central.net]

G68 - Vehicle Speed Sensor Info please

That's correct for S2 James. Pin 8 on T26 (yellow plug) is brown wire 0V connection while the G22/G68 input arrives on T26a (blue plug) on pin 20 as a red / brown wire.

PS - see attached schematic snippet showing July 1993 when the transition from G22 to G68 was made. That implies a technology / sensor change between G22 and G68 but I haven't explored what / why yet.

IMG_3383.JPG

[Error404]

Yup, it changed from reed switch to hall sensor. The later instruments with the Motorolla chips are not polarity sensitive, they will accept either pull to earth or +ve pulse.
I think it even says on one of the wiring schematics there was a date change to hall sensor

[UrS4boy]

PS - see attached schematic snippet showing July 1993 when the transition from G22 to G68 was made. That implies a technology / sensor change between G22 and G68 but I haven't explored what / why yet.

Yup, it changed from reed switch to hall sensor. The later instruments with the Siemens chips are not polarity sensitive, they will accept either pull to earth or +ve pulse. I think it even says on one of the wiring schematics there was a date change to hall sensor

Thanks for this info guys. I apologize for "correcting" people in the past that reported "G68" vehicle speed sensor errors, telling them that it was a "G22" error. I had zero idea that there was a change in technology. Any idea of the PNs involved? I need to use this new info to update my "G22" info:

http://forums.quattroworld.com/s4s6/msgs/168463.phtml

Dave F

[UrS4boy]

Any idea of the PNs involved? I need to use this new info to update my "G22" info

I just checked the range of the 012409191D "G22" application and it goes from 1988 to 2005 across the C3, C4, C5 and B3, B4 and B5 lines so they might have changed the technology without changing the PN. Sort of like the switch from the 4 pin F76 MFTS to the 3 pin MFTS.

Here is a photo of the connector end of a "012409191D " that is currently (pun not intended) available:

https://www.ecstuning.com/Search/012...m68aAnSr8P8HAQ

[Error404]

The hall sensor variant will be 3 pin

[UrS4boy]

The hall sensor variant will be 3 pin

That would require a harness change of some sort. Any idea of the PN on a post 1993 G68?

[Error404]

Agree, needs a +ve supply - I had to add that on mine.
Perhaps then they just homogenised the sensor coding to "avoid" confusion?

[UrS4boy]

Agree, needs a +ve supply - I had to add that on mine.
Perhaps then they just homogenised the sensor coding to "avoid" confusion?

Any PN info on this new one? As for avoiding confusion, they've obviously failed, at least amongst the uncertified amateurs here.

[UrS4boy]

Just checked my Robert Bentley C4 wiring diagrams in Vol.3 and Audi seemed to stick with a 2 pin G22 all the way to the end (1997 sedans and avants and the 1998 C4 A6 avant). Only change I saw was a couple of references to the G22 signal also going to the engine control module (V6) and/or the ABS (EDL) module directly, before the G21 speedometer.