My speedo is playing up.It sometimes comes on whilst driving but most of the time doesnt work.A garage said it was an electronic type.Service engine soon light has been displayed on the dash and when connecting the diagnostics machine it came back with the fault code of the speedo.Is this something that could be easy to fix as the garage wanted $400!

Year, model, engine? If the ECM is throwing a code, your speedometer is probably ok but we'd need more info on your car first to be able to tell you how to diagnose the problem.

Lou

car year is a 1992 z28 convertible 5.0 TPI Im not sure what Code the Diagnostics machine gave maybe 24.

Don't tell me your car is black too.

Anyway, I'd check the wiring from the tailshaft to the ECM (yellow and purple wires). I think they go in throught the passenger side, with other engine data signals.

It could be just a loose plug, what do you know. If you have a friend whose VSS you could borrow and see if it makes your speedometer work, that would be great. Or you can pull yours out of the tailshaft and try to spin it by hand and see if the gauge moves at all (with key on).

You could also hook up a function generator to the VSS connector and generate a square wave signal of frequencies 1-100Hz and that should give you approx 1-90mph reading.

If none of this works, you can then put the function generator directly on the ECM connector C1 (the smaller black one), pin B10 (yellow). If that moves the speedometer, it's the wiring.

Hope this helps any.
Lou

Thanks for all your help! I will certainly try that.