speedo/odo issue

[vfstyles]

im posting this over here as i didnt get any response on m42club........

Im trying to get my speedo/odo to work. It worked when first got the car but it no longer does.

I have two clusters. I've opened them both and inspected the gears, batteries and SI board. The VDO Si board has battery corrosion

Inside the motometer, the gears spin freely and the board is free of damage. I checked the voltage of the battery and it was good.

I installed a new speed sensor in the diff and it still doesnt work. It was a cheap and simple part to install and i thought that it would cure my problem so i tried it unsuccessfully. This leads me to think that my problem lies within the harness or wires.

My questions:
Can someone explain to me how the VSS and speedo, dme interact?
does anyone know the a/c ouput of the VSS? I checked resistance, but want the voltage outputs when running. My reading on my DMM was 0-.003v
can voltage outputs be read with a digital multi-meter or is the scale too finite?
i have an osiliscope if needed

[jlevie]

The speedometer should work, even with a dead SI board. A dead speedometer isn't likely to be the cause, since you've tried two clusters and the odds of both having a dead speedometer aren't that high. The signal from the speed sensor routes directly into the speedometer and is best checked with an o-scope (should be a square wave when the rear wheels are turning).

Have you ohmed out the connection from the cluster to the speed sensor connector? Are the fuses for the cluster good?

[Vagcycle]

Yeah, i'd check the fuses, I believe they are like 8, 10 , 12.

[rkettner]

i'm trying to determine why my speedometer reads 10% high. i chaged the entire diff as well as the sensor. my tires are the same diameter as stock too.

what gives? wrong coding plug?

[Rogan]

i'm trying to determine why my speedometer reads 10% high. i chaged the entire diff as well as the sensor. my tires are the same diameter as stock too.

what gives? wrong coding plug?

coding plug is tach only, IIRC..

Are the VSS sensors the same, for all diff ratios? This, I do not know.

My speedo reads high, as well, but not linearly. Testing with my GPS...


25MPH:
GPS = 25
speedo = 25-26
OBC = 25

35MPH:
GPS = 35
speed = 39
OBC = 36

50MPH:
GPS = 50
speedo = 56
OBC = 52

65MPH:
GPS = 65
speedo = 73
OBC =66

OBC is really close to GPS reading, however, the speedo is progressively off. I'd test it with a wave gen if I had one.. :crazy:

[rkettner]

why would the obc speedo and the actual speedo read differently?

i'm learning!

[Rogan]

no friggin clue, honestly.