2009 chevy 2500HD brake issue

2009 chevy 2500 HD work truck, brake light is on, says service brake system. Tried reading codes, no codes found. Pads/rotors excellent shape. Didn't see anything obvious. Checked wheel speed sensors just in case, they're good. ABS light not on, just the brake light. E brake doesn't work in this truck and is strapped up. Used to be if that brake light came on its because my foot smacked that pedal and needed to be released. Not working now to turn light off. And when I press the brake firmly in park, it feels like the ABS is activating.