Brake Pressure Warning Switch?

[BadCompany750]

1998 ECSB C1500 5.0

I have a (!)(P) BRAKE warning light on my dash. The guy I bought it from said that the truck sat for "a while". He replaced one of the slave cylinders in the rear brakes because it was leaking. The pedal doesn't feel too spongy. I've bled the brakes but that didn't help the light. I did find out that when I unplug the brake pressure warning switch on the aide of the ABS unit, the light goes out. I grabbed some from my local Pull a Part. Will I have to bleed the ABS unit if I replace the switch? I assume so since the switch has a rubber o-ring.

Thanks

 

[Schurkey]

Don't replace the switch yet.

FIRST, stamp the brake pedal HARD with the engine running so the power booster is working. Does the light go out and stay out? If it does, you should totally flush the brake fluid using a scan tool to chatter the valves in the ABS unit, per the instructions attached to this post.

If it stays lit, you need to re-center the pressure differential spool valve in the combination valve, under the switch. There's several methods. You can unscrew the switch, and manually re-center the valve with a small screwdriver. You can bleed the front brakes using brake-pedal pressure, to force the spool valve to it's centered position...unless the spool valve is pushed to the rear hydraulic side. In that case, you need to bleed the rear brakes to push the spool valve towards the front hydraulic system.

And then you need to flush the brake fluid using a scan tool per the attached instructions.

In any event, it's really unlikely to be a faulty switch. It's enormously more likely that the spool valve is stuck either too far to the front hydraulic system, or to the rear hydraulic system, and merely needs to be centered.