Hi,

I was thinking of doing a little project with my Octavia LX MK1, and would like to know what sort of signal comes from the speedo sensor. Has any one measured it before? or is there anything on the forum about it?

I know that the signal comes in on a green wire to plug A at the rear of the instrument panel on pin 28, and I could measure it, but I don't really want to take it out again and disturb it now that it is working fine, and the problem with the gauges seems to be fixed.

Does any one know the frequency range at various speeds and the waveshape?

Thanks, as any ideas would be much appreciated.

Soviet.

Not sure whether the last section of this is any use to you. It sounds like an FM signal between 0 and 12V.

Testing road speed signal

If a fault exists in the cruise control system at

the speedometer, it is necessary to test whether

a signal exists at the speedometer.

- Connect vehicle system tester V.A.G 1552

⇒ page 90-3.

- Read measured value block ⇒ page 90-12.

- Select display group number 001 and con-

duct a road test.

If the road speed appears in the display of the

vehicle system tester V.A.G 1552, the dash

panel insert is faulty and must be replaced.

If no road speed appears in the display of the

vehicle system tester V.A.G 1552, it is then nec-

essary to test the signal at the multi-pin plug

connection at the dash panel insert.

- Remove dash panel insert ⇒ page 90-29.

- Connect test box V.A.G 1598 with adapter

V.A.G 1598/25 to the blue 32-pin connector.

- Use multimeter V.A.G 1526 A to measure

the voltage between contact 28 and vehicle

earth.

- Move the vehicle back and forward slightly.

Specifications:

The vehicle must rise from 0 V to about 12 V

and drop again to 0 V (pulsating direct voltage).

If the test is not o.k., test the cable connection

to the road speed sender.

- Test cable connection according to current

flow diagram.

⇒Current Flow Diagrams, Electrical Fault

Finding and Fitting Locations binder.

If the cable connection is o.k., the road speed

sender should be replaced.

Not sure whether the last section of this is any use to you. It sounds like an FM signal between 0 and 12V.

Testing road speed signal

If a fault exists in the cruise control system at

the speedometer, it is necessary to test whether

a signal exists at the speedometer.

- Connect vehicle system tester V.A.G 1552

⇒ page 90-3.

- Read measured value block ⇒ page 90-12.

- Select display group number 001 and con-

duct a road test.

If the road speed appears in the display of the

vehicle system tester V.A.G 1552, the dash

panel insert is faulty and must be replaced.

If no road speed appears in the display of the

vehicle system tester V.A.G 1552, it is then nec-

essary to test the signal at the multi-pin plug

connection at the dash panel insert.

- Remove dash panel insert ⇒ page 90-29.

- Connect test box V.A.G 1598 with adapter

V.A.G 1598/25 to the blue 32-pin connector.

- Use multimeter V.A.G 1526 A to measure

the voltage between contact 28 and vehicle

earth.

- Move the vehicle back and forward slightly.

Specifications:

The vehicle must rise from 0 V to about 12 V

and drop again to 0 V (pulsating direct voltage).

If the test is not o.k., test the cable connection

to the road speed sender.

- Test cable connection according to current

flow diagram.

⇒Current Flow Diagrams, Electrical Fault

Finding and Fitting Locations binder.

If the cable connection is o.k., the road speed

sender should be replaced.

Hi,

Many thanks, as this could well be of use to me. as there may be a way of measuring the signal using Vag-com and the measuring blocks. I have not had Vag-com for very long and so will need to experiment. Some other members may know about this.

The most interesting bit is about the voltage (pulsating direct voltage) which rises to 12 v and then drops to 0v when the vehicle is moved back and forward slightly. At least this gives me something to go on, thank you.

Some one at work was telling me that he thought that the average frequency was 100 Hz over the speed range, but may be, he just plucked this out of thin air.

I could I suppose get a sensor from the scrap yard and measure it some how to save taking my instrument panel out again, and risk the gauges playing up.

My little project was to fire the signal in to a LM2917N freq. to voltage converter, and then connect it to a driver for a three section LED display. If ever my instrument panel plays up in the future, at least I will have an indication of my speed, and can stay with in the law.

I am sure that there are many commercially availiable made up ones, but this won't give me any fun.

I love fiddling in my spare time, and thought that it may be something to do at Christmas, to escape the normal drivel that is dished up. You know the thing, the Queens speech,

Disney films, Bedknobs and broomsticks, and of course the horrendous Chitty, chitty, bang, bang. If I see it once more then I shall, put a revolver to my head and pull the trigger. Nothing like a bit of Russian roulette to get the party, of with a bang.

Disney films/cartoons are so noisy and American, Arhhh!

Many thanks for your help, as it has given me food for thought.

Soviet (dig up Brezhnev and resuscitate)

Does anyone know if it is possible to look at the speedo sensor output wave using measuring blocks on Vag-com? Has any one, ever done this?

I have version 704.1.

Soviet