Cranked up truck, pedal sank to the floor.

If you did not use a scanner (brake shop/dealer) to open up the ABS system valves for bleeding, you probably still have air in the system.

This would make the pedal be low. With the pedal being way down the booster will hiss.

"Repair Guides" is at the top right side of our pages. There is more brake information in there (if you click into it). I went ahead and posted this link from there for you.

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

Let us know how it is going.

The Medic

If you or your pals ever need assistance, come on back, there's a bunch of us on this end that do their darndest to get people mobile again.

Thanks for giving us a shot, The Medic

If you are not losing any brake fluid from the reservoir, a defective master cylinder is the likely suspect. It is normal and acceptable for the fluid level to not be at the top. That is simply a sign the brakes need to be inspected in the near future for normal wear. Do not add any brake fluid as long as the level is above the "Min" mark.

If the fluid level is going lower as you pump the brake pedal, there is an external leak that must be diagnosed and repaired. You will see a wet spot or puddle someplace underneath the truck. Also, be aware that on any vehicle more than about a year old, running the brake pedal all the way to the floor, regardless of the cause, will often damage the master cylinder due to the crud and corrosion that build up in it over time. It is not unusual to need a replacement master cylinder in addition to the original repair.

Good afternoon.

Did you use the procedure with a scan tool to bleed the system?

Roy

ABS Automated Bleed Procedure:

Notice: When adding fluid to the brake master cylinder reservoir, use only Delco Supreme II, GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container. The use of any type of fluid other than the recommended type of brake fluid, may cause contamination which could result in damage to the internal rubber seals and/or rubber linings of hydraulic brake system components.

Notice: Refer to Brake Fluid Effects on Paint and Electrical Components Notice in Service Precautions.

Important: This procedure may be performed on all vehicles EXCEPT those equipped with option code JL4, Vehicle Stability Enhancement System (VSES).

Important: The base hydraulic brake system must be bled before performing this automated bleeding procedure. If you have not yet performed the base hydraulic brake system bleeding procedure, refer to Hydraulic Brake System Bleeding (Manual).

1. Install a scan tool to the vehicle.
2. Start the engine and allow the engine to idle.
3. Depress the brake pedal firmly and maintain steady pressure on the pedal.
4. Using the scan tool, begin the automated bleed procedure.
5. Follow the instructions on the scan tool to complete the automated bleed procedure. Release the brake pedal between each test sequence.
6. Turn the ignition OFF.
7. Remove the scan tool from the vehicle.
8. Fill the brake master cylinder reservoir to the maximum-fill level with Delco Supreme II GM P/N 12377967 (Canadian P/N 992667) or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container.
9. Bleed the hydraulic brake system. Refer to Hydraulic Brake System Bleeding (Manual).
10. With the ignition OFF, apply the brakes 3-5 times, or until the brake pedal becomes firm, in order to deplete the brake booster power reserve.
11. Slowly depress and release the brake pedal. Observe the feel of the brake pedal.
12. If the brake pedal feels spongy, repeat the automated bleeding procedure. If the brake pedal still feels spongy after repeating the automated bleeding procedure inspect the brake system for external leaks. Refer to Brake System External Leak Inspection. See: Hydraulic System, Brakes > Component Tests and General Diagnostics
13. Turn the ignition key ON, with the engine OFF; check to see if the brake system warning lamp remains illuminated.
14. If the brake system warning lamp remains illuminated, DO NOT allow the vehicle to be driven until it is diagnosed and repaired. Refer to Symptoms - Hydraulic Brakes. See: Hydraulic System, Brakes > Symptom Related Diagnostic Procedures
15. Drive the vehicle to exceed 13 kph (8 mph) to allow ABS initialization to occur. Observe brake pedal feel.
16. If the brake pedal feels spongy, repeat the automated bleeding procedure until a firm brake pedal is obtained.

You may have to do it several times. Tthen also do the manual bleed as well.

If you still have no pedal, you may need a pressure bleeder. You will have to force the air out of the system with pressure. You can rent one at a parts store.

Roy

Okay, keep me updated.

Roy

We did not get any response whether it worked or not.

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Air is most likely the issue and it is tough to get all the air out. Pressure bleeders are the best way to force out all the air.

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

Roy

I would use vice grips and clamp off the brake hoses and see if you still have no pedal or is the pedal high and hard.

This way we can narrow where is issue is located.

Roy

Good find. The bleeders need to be at the top of the calipers, not at the bottom.

Roy