VS speedo giving an incorrect reading...

[gtsmoker]

Brett, can you read my original text and see if you have any ideas?? I cant work it out.

 

[Brett_jjj]

Ive just been checking out the wiring diagram in the workshop manual to see where the speedo etc get their speed signal, and the speedo gets its signal from either the speed sensor on a manual transmission,or from the ECU on an auto trans,via a Violet/white wire,and so does the trip computer, if one is fitted,but I cant for the life of me see where the speed alert module gets its speed signal from,cars that dont have the trip computer fitted,usually have the speed alert fitted instead,so its really got me stuffed.Theres just no wire from the speed alert module to the speed sensor or ECU.Id try to set the speed alert to the digital speedo mode like I mentioned in the above post, and see how much difference there is between the speedo reading and the digital speed reading on the speed alert..if its the same,then the speed alert module might be stuffed.It just pulls out of the dash and unplugs,so they are easy to change over if thats the case.

 

[hako]

If you read the owners handbook (the one in the glovebox), it says something about a fudge factor built into the speed alert - means that if you dial 100kph into the speed alert, it will only sound when you hit 105kph or thereabouts. I'd guess that it's designed that way because normal car speedo's traditionally over-read....this makes you think you are going faster than you actually are.:smoking:

 

[Chappo_1]

Do you have a GPS you can use?
According to my GPS, my speedo reads 5km under. When my speedo says 60km/hr, the GPS says 55km/hr.
Who's to say which is correct though :/

 

[adrian123443]

I have a Vs berlina when I'm travelling at 100 k's my gps reads 92, I found the easiest solution is just to go 108