Olds vs Pontiac same,but different

I'm having a problem with my '90 Silhoutte.
The odometer& trip O.D. don't work.
The speedometer is off my about 20 mph.
I don't see a speedometer cable. Are they
electric? Any other info?

Indeed this is electric. A small "magneto" on the transaxle generates pulses at the rate of 4000 per mile. These pulses , through the ECM, drive a step motor that increases mileage readings and the rate of the pulses generate a square wave whose average voltage is proportional to speed.

THe "book" says (in '90, this is a 3.1 eh?):
- check for open contact at vehicle speed sensor (top of Transaxle)
- defective sensor buffer or defective contact at buffer (behind instrument panel compartment, above convenience center(heater/AC)
- defective speed sensor (less probable)

A CODE 24 should come with the kind of problem you have.

Thanks LMP! I'll check it out.

So it would seem that the problem I had with my guages
was with the guages themselves.I ended up buying 2 more sets
from junkyard and still had to use part of the orginal
set to get the guages useful & still lost the rpm guage.
Seems each individual piece such as speedometer and rpm
guage uses a tiny motor to operate.Similiar probs appeared
on the other guage clusters as well. What a pain in the ASS!!

Well indeed GM also said that in last resort, the instrument panel module itself might be the culprit. For several gauges to be in trouble together all at a sudden, there must be a common problem. In similar installations, there use to be a specific power supply - generally delivering 5 volts - for the operation of the instrument panel, but I see no reference to that in the GM book: such a power supply - it can be a simple voltage limiter - is necessary to keep instruments calibrated as the battery and system voltage varies . May be it is an integral part of the I/P module but then, the other ones you have tried should have solved the problem - unless you are very unlucky. I'm puzzled.

What source are you reading from?

1993 Pontiac Transport Service Manual , the very one they use at GM service centers. (bought from GM just as I bought the car).