Hot to bleed an abs system 2008 Chevy trailblazer

use a vacuum pump, have someone keep brake fluid full, do not it go low or you will introduce air back into system,
look online for bleeding brakes using hose and jar and brake fluid. either of them is easy. HF also sells his item.

Amazon com MV8000 Automotive Tune up and Brake Bleeding Kit Automotive

Its possible it could be the master cylinder itself, It should always push fluid. Does the car have ABS? It could also be inside the ABS module if it does. I am familiar with brake systems and diagnostics, just not familiar with this year olds whether it has abs or not.

possibly a faulty caliper

Here's how to abs bleeding?

try bleeding your ABS block first, if that doesn not work could need a master or proportioning vavle. Some scan tools are capable of bleeding the ABS system on some vehicles, and some you have to bleed manually.

sometimes if you leave the bleeder screw open it will gravity bleed the cylinder.Make sure master cyl is full and do one wheel at a time.I have seen this work, I have done it.

if you didn't bleed the lines after putting the master in. then there is a good chance there is air in the lines now. may go through a quart of brake fluid before all the air is out. remember to start at r-rear/ l-rear/ r-front/ l-front last.will take some time. don't forget to adjust the rear brake while your there to help with the pedal

Try having the dealer flush and bleed your system. It is very hard to bleed ABS systems yourself and have safe brakes that still work afterward. Bleeding non-ABS brakes yourself is easy not the same for ABS brakes. Valving, sensors and what-not require a tech and the correct equipment in my opinion. You do it wrong and you could ruin your ABS system. Do that and see if they firm up. I replaced my brake shoes/pads at the same time all new everything in back, drums/springs everything and new rotors up front. then I had the chevy dealer flush, refill and bleed system. Stiffer pedal and brakes work better. Keep in mind the brakes on 99 Tahoes are inaedequate, require new rotors often, heat up and fade/glaze pads regularly. I replace my pads long before they wear down because they glaze up and start fading early. I'll rough em up once maybe, next time, new ones. Every two brake jobs, new rotors for me. Just how it is. They will stiffen a bit and work better but they will never be awesome brakes. Just how it is on 99 and earlier Tahoes. Hope it helps. Very important to bleed correctly though. I'll bleed my 83 Toyota 4x4 myself but not the Tahoe.

Check the pads/rotors to see if they need to be replaced.
Check the brake fluid level. If low it could mean the pads/rotors need to be replaced. If replacing also replace the brake fluid.
Two years probably means you need a brake job.

Otherwise you may have air in the brake lines which you can bleed off.

Chevys are bare to blead, especially if it has ABS. Chevy dealers actually use TECH 2 / their computer to blead ABS systems properly. With it, they open the ports in ABS module, which helps the brake fluid flow. Unless of course you have ripped the sensor wire for ABS by accident.