I am getting a Code 4 on a 91 S10 with RWAL brakes. Code 4 is an anti-lock valve stuck open. Which valve are they talking about? There are other codes for the Isolation and Dump valves. Anyone have any idea.

Thanks
JMW

I think it is the valve reset switch in the ABS pcm.
Check your PM.

I already replaced the ELectronic Control Unit.
The Schmatic I have shows the reset swith being part of the
Isolation/dump valve module which is attached somehow to the
combination valve. I not sure exactly what it does.
I am not sure how to test it without just replacing it,
but it is a fairly expensive part and it looks like a pain to change.

I already replaced the ELectronic Control Unit.
The Schmatic I have shows the reset swith being part of the
Isolation/dump valve module which is attached somehow to the
combination valve. I not sure exactly what it does.
I am not sure how to test it without just replacing it,
but it is a fairly expensive part and it looks like a pain to change.

As far as I can ll the reset switch is made inside the ABS module/pcm.
Did you get the PM I sent?
If so go threw the ohm check out test outlined in it.
Let us know how the test goes.
MT