Service Brake System Msg & Light

We have an 06 Uplander and had been experiencing an intermittent Service Brake System message and light. This is the service brakes not ABS message.

It was needing pads so I thought maybe it was just low brake fluid. I replaced the front pads today and now the light and message are constant. I didn't open anything up. The pedal feels fine.

Any ideas what might be causing it?

As first fix, I would bleed the brakes. Sounds like air in brakes or air bubble within ABS unit. If that doesn't work, get a reader and "read its code". Its code will advise if sensor problem or some other problem. Bleeding brakes with 2 people should be easy. re: One person to press the brake peddle and a different person to wrench its bleed screw (on further wheel hub working closer to Master Brake Cylinder).

Good luck...