Chevrolet Repair: 1991 1500 brakes, line ports, rear brakes

Question
Replaced rear brakes complete including cylinders(had a leak). Pedal soft when engine running. Bled lines over and over. Tried new master cylinder and booster. Idiot light says I needed brake module. Tried that. Pedal still soft and not sure what else to try. Help.

Answer
HI ALAN, A BOOSTER WOULD NOT CAUSE A LOW PEDAL, IF BOOSTER WAS BAD THE PEDAL WOULD BE AS HARD AS ROCK NO POWER ASSIST. BEFORE YOU PUT THE MASTER CLYLINDER ON THE BOOSTER DID YOU BENCH BLEED IT ?  IF NOT REMOVE THE M/C AND BENCH BLEED IT REAL GOOD. THE WAY THE M/C SITS ON THE BOOSTER MOUNTED IN THE TRUCK IT WILL TRAP AIR IN THE CHAMBER AND YOU CAN NOT REMOVE IT UNTILL IT IS BENCH BLED [SITTING LEVEL] I WILL ASSUME YOU SCANNED THIS AND THERE WAS A CODE FOR THE BRAKE MODULE FOR THE REAR ABS ??? THIS MAY HAPPEN IF THERE IS NOT ENOUGH PRESSURE FROM THE MASTER CYLINDER. SO AFTER YOU BENCH BLEED THIS M/C I WOULD PUT 2 PLUGS IN THE LINE OUTLETS AND BLEED IT WITH THE PLUGS IN THE LINE PORTS ON THE M/C..DO NOT HOOK THE LINES UP JUST YET. ONCE THE M/C IS BLED TIGHTEN THE PLUGS UP TIGHT AND SEE HOW THE PEDAL FEELS LIKE THIS..IF PEDAL IS GOOD AT THIS POINT WE NOW KNOW THE M/C IS GOOD .... NOW REMOVE THE PLUGS AND PUT THE BRAKE LINES BACK INTO THE M/C AND BLEED IT AGAIN AT THE M/C. START IT UP LIKE THIS AND SEE WHAT YOU GOT NOW.. IF PEDAL IS STILL LOW YOU WILL NEED TO ISOLATE THE PROBLEM. GO TO THE NEXT AREA, SUCH AS PROPORTIONING VALVE,IF THIS HAS ONE ]BECAUSE OF THE ABS MODULE] SOME DO SOME DONT..BLOCK OF THE LINE BEFORE THIS UNIT AND SEE IF PEDAL IS GOOD,IF SO YOU KNOW THAT TO THIS POINT ALL IS GOOD.YOU WILL NEED TO DO THIS ALL THE WAY TO THE BACK BRAKES UNTILL YOU FIND THE PROBLEM..IF THE ABS MODULE WAS OK BEFORE THE BRAKE JOB IT SEEMS STRANGE THAT THE MODULE WOULD NOW BE BAD..UNLESS YOU GOT SOME DIRT OR SOMETHING INTO THE UNIT WHEN BLEEDING IT.
I HOPE THIS HELPS YOU AND IF YOU NEED MORE INFO GET BACK TO ME,,,TOM..