Are you saying someone swiped that part or it fell off? How did the system work before without it? There are numerous variations to the anti-lock brake systems, but very often a hydraulic controller can be modified to work in more than one application. If the switch you're looking for wasn't used originally, where are you going to plug it into?
If by "missing" you mean it is broken off, that might explain why the warning light turned on. Regardless of the cause, there will be a diagnostic fault code stored in the computer related to that. Normally parts for ABS controllers are not available, often even to dealers. External switches may be available, but GM is famous for having a huge number of different parts for one application. If that switch is available, they may need to order it based on your vehicle's I.D. Number or the date of manufacturer. You'll find both on the driver's door sticker.
Two other possibilities are to find one on a similar vehicle in a salvage yard or to contact one of the companies that rebuild hydraulic controllers. Some of these aftermarket companies are real good to work with and are happy to supply little parts. You can find them through internet searches, but you'll have to call them to try to order little parts. They don't usually list parts on their web sites because mechanics aren't expected to repair these assemblies in the field. The people there very often know a lot more about what you need than the dealer's parts department people. The dealer's people basically only know what GM wants them to know and provides training for, and that is to sell assemblies, not the parts to fix those assemblies. That has been one of their poor business practices since the mid '70s. Ford, not GM, is the company that does a real poor job of making parts available for vehicles more than four or five years old.
I don't know how you diagnosed this but it leaves me curious as to why it caused the brakes to lock. We know there's no other underlying problem with the base brake system since the brakes aren't continuing to lock, but it typically takes a mechanical failure inside the controller to cause that, and that's not real common.
You might look at the Rock Auto web site to see if you can see that switch on one of their pictures. They list two different ABS systems. I looked under "Electrical - Switches" and didn't see a listing, but under "Brake / Wheel Hub" they list the "ABS Modulator Valve" that shows a switch. At least that would give you something to reference to when asking for this part.
Monday, January 13th, 2014 AT 7:17 PM