Olds vs Pontiac same,but different

[1Bad89SC]

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?

[LMP]

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.

[1Bad89SC]

Thanks LMP! I'll check it out.

[1Bad89SC]

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!!

[LMP]

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.

[1Bad89SC]

What source are you reading from?

[LMP]

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