I had the same problem on my 2000 Astro.
Under the driver side knee bolster there is a harness with shunt ( cap) and 8 wires of different colors of blue green yellow, white with blue and so on.
make sure that cap did not came lose ( The cap does the bridging where needed).
Just putting that cap back solved my problem.
Instrument cluster is another place I would look for the proble if the first one doesn't help, but before geting to Instrument cluster you need to disable the airbags. Stay away from Yellow thicker wires they are for airbag..
Now, there is one thing...
Do you have an access to a OBDii scanner? Preferabley with ABS capability.
OR is there an auto parts store in your area that offers free scanning?
Let us know how it went.