brake petal went to the floor on 2003 Chevrolet Silverado 2500 HD

Brake petal is very soft, still have some brakes. replaced master cylinder and problem is still there

1 answer
You may not have gotten the air out of the brake system, especially if you have ABS brakes. If you do, there's a 'Scan Tool Bleeding Procedure' which requires a scanner to bleed the ABS system. You may need to go to a GM specialist with a scan tool to get the brakes bled.
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http://repairpal.com/directory?address=06883&car_brand_names=Chevrolet