After replacing brake boost and Master cylinder the brake pedal goes to the floor

MOMMY051615

MEMBER
2004 CHEVROLET IMPALA
3.4L
6 CYL
AUTOMATIC
170,000 MILES

I just recently purchased a new brake booster and a new master cylinder for my car. We have bled the brakes three times and my brake pedal is still going to the floor and there is no pressure. My passenger side when we tried to bleed it was as if there was clog somewhere, so we left the plug off to let gravity kick in. If this does not work what else could be my problem?

1 Reply

ASEMASTER6371

MECHANIC
52,797 POSTS

Good morning.

There is an automated brake procedure for the ABS system. Air gets trapped in the unit and you need a scan tool to get the air out. It will not bleed out by manually bleeding the system.

Below is the procedure. You will need a real scan tool that can access the ABS for this operation.

Roy

Automated Bleed Procedure

Notice: The Auto Bleed Procedure may be terminated at any time during the process by pressing the EXIT button. No further Scan Tool prompts pertaining to the Auto Bleed procedure will be given. After exiting the bleed procedure, relieve bleed pressure and disconnect bleed equipment per manufacturers instructions. Failure to properly relieve pressure may result in spilled brake fluid causing damage to components and painted surfaces.

1. Raise the vehicle on a suitable support. Refer to Vehicle Lifting.
2. Remove all four tire and wheel assemblies.
3. Inspect the brake system for leaks and visual damage. Refer to Brake Fluid Loss or Symptoms - Hydraulic Brakes. Repair or replace as needed.
4. Inspect the battery state of charge.
5. Install a scan tool.
6. Turn ON the ignition, with the engine OFF.
7. With the scan tool, establish communications with the EBCM. Select Special Functions. Select Automated Bleed from the Special Functions menu.
8. Bleed the base brake system.
9. Follow the scan tool directions until the desired brake pedal height is achieved.
10. If the bleed procedure is aborted, a malfunction exists. Perform the following steps before resuming the bleed procedure:
If a DTC is detected, refer to Diagnostic Trouble Code (DTC) List and diagnose the appropriate DTC.
If the brake pedal feels spongy, perform the conventional brake bleed procedure again.
11. When the desired pedal height is achieved, press the brake pedal in order to inspect for firmness.
12. Remove the scan tool.
13. Install the tire and wheel assemblies.
14. Inspect the brake fluid level.
15. Road test the vehicle while inspecting that the pedal remains high and firm.