Low brake pedal

[butch h]

I am working on an '02 Sierra with brake issues. The truck ('02 Sierra extended cab 4x4 with the 6.0 gas engine and automatic transmission) came in with a left front brake hose leak. The owner said he had no brakes after the line blew. I clamped off the leaking hose and was able to put the truck on the lift, and replace the hose. The owner also said he did not have any rear brakes, but the rotors were not rusted and they looked the same as the front rotors. I cleaned and lubed the slider pins as a precaution. After bleeding the brakes, I checked for any anti-lock issues/codes and found none. Someone had previously replaced all the brake tubing, so I'm unsure of any routing, or placement errors. With the engine off and the vacuum exhausted, the brake pedal looks and feels right. When the engine is started, the pedal goes almost to the floor, although it does stop the truck. Any ideas as to why there's so much travel? Any input would be appreciated.
Thanks.

[maxwedge]

Proper bleedig of these trucks requires use of a scanner to bleed the abs, assume you did this?

[butch h]

I didn't know a scan tool was required, but I could not see a bleeder on the anti-lock module. If you could run me up to speed on this procedure, including the minimum scan tool requirement, I would certainly appreciate it, as this would explain this owner and the former owners dissatisfaction of brake feel.
Thanks.

[maxwedge]

Correct, the abs must be bled using the indivdual wheels, this is required if air got into the abs unit, only professional grade scanners have the ability to actuate the internal solenoids in the abs to get the trapped air out. You can google bleeding GM abs for in depth info.