2002 Chevrolet Trailblazer Brakes

Try bleeding your brakes thoroughly. Start with a caliper farthest away from the master cylinder and work your way closest. If that does not work you may have a master cylinder going bad

it sounds like you have air in the system,try bleeding it as described earlier.also this vehicle may require a scan tool to do an automated bleeding of the abs module.if you can not get a better pedal with conventional bleeding you might have to take it to a shop or find someone with a scan tool that will do the bleeding.