Okay, I'm starting over with a new thread looking for some ideas on this.

The brake pedal goes way lower than it should. How low seems to vary slightly, but it doesn't really "pump up". I replaced the master cylinder. It is exactly the same.

When you first start the car, no warning lights come on. The BAS/ASR light comes on the first time you press the brake pedal. I also replaced the brake light switch with no change to the light behavior.

I have noticed when you press the pedal, the first tiny bit of travel has very little resistance. Then it hits a point where you can feel it sort of catch and there is more resistance. When you pass the catch point, that's when the light comes on.

Is there anything about the W140 brake booster or ABS system that would cause a low pedal if it malfunctioned? Could a faulty BAS module cause this behavior? I've wondered if it has something to do with one of the sensors mounted in the brake booster. The pedal takes up way too low, but the brakes seem to work OK and ABS and ASR are both functional.

And yes, I know I need to get the 38-pin codes read. But until I'm able to get that done, I'm trying to brainstorm a little bit.

__________________
Jay
1998 S320

Jay
How old are your brake hoses? My 99 S500 had a low pedal, even after pressure bleeding.
New hoses (from MB no Trucktec) on all four corners corrected the problem. They are a maintenance item. Look for cracks or dry rot on the rubber.