Brake pedal goes to floor I must have got air into the system

Tiny
BUMPER51
  • MEMBER
  • 2007 BUICK LUCERNE
  • 3.8L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 112,000 MILES
I replaced the brake pads on all four brakes. Had a tough time getting the pistons pushed back in, so I opened the bleeders. One bleeder would not stop leaking so I replaced it. That is where I must have got air into the system. After repeated attempts at bleeding, I gave up and took car to my mechanic. He has tried new parts on almost everything, master cylinder, abs module, rear calipers and still cannot get a pedal. On test drives, sometimes the rear brakes will lockup when applied.
Sunday, March 11th, 2018 AT 11:48 AM

12 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon.

There is a bleeding procedure that requires a scan tool to bleed the system. Basic bleeding will not work without this procedure.

Roy

Antilock Brake System Automated Bleed Procedure

Caution: Refer to Brake Fluid Irritant Caution.

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

Important: Before performing the ABS Automated Bleed Procedure, first perform a pressure bleed of the base brake system. Refer to Hydraulic Brake System Bleeding (Manual) Hydraulic Brake System Bleeding (Pressure). The automated bleed procedure is recommended when one of the following conditions exist:

* Base brake system bleeding does not achieve the desired pedal height or feel

* Extreme loss of brake fluid has occurred

* Air ingestion is suspected in the secondary circuits of the brake modulator assembly

The ABS Automated Bleed Procedure uses a scan tool to cycle the system solenoid valves and run the pump in order to purge any air from the secondary circuits. These circuits are normally closed off, and are only opened during system initialization at vehicle start up and during ABS operation. The automated bleed procedure opens these secondary circuits and allows any air trapped in these circuits to flow out toward the brake corners.

Performing the 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 and support the vehicle. Refer to Vehicle Lifting.
2. Remove all four tire and wheel assemblies.
3. Inspect the brake system for leaks and visual damage. Refer to Symptoms - Hydraulic Brakes. Repair or replace components as needed.
4. Lower the vehicle.
5. Inspect the battery state of charge.
6. Install a scan tool.
7. Turn the ignition ON, with the engine OFF.
8. With the scan tool, establish communications with the ABS system. Select Special Functions. Select Automated Bleed from the Special Functions menu. The Automated Bleed function will take 5 to 20 seconds.
9. Follow any screen instructions.
10. Remove the scan tool.
11. Raise and support the vehicle. Refer to Vehicle Lifting.
12. Following the directions given on the scan tool, pressure bleed the base brake system. Refer to Hydraulic Brake System Bleeding (Manual) Hydraulic Brake System Bleeding (Pressure).
13. Follow the scan tool directions until the desired brake pedal height is achieved.
14. 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 - Vehicle and diagnose the appropriate DTC.
If the brake pedal feels spongy, perform the conventional brake bleed procedure again. Refer to Hydraulic Brake System Bleeding (Manual) Hydraulic Brake System Bleeding (Pressure).

15. When the desired pedal height is achieved, press the brake pedal to inspect for firmness.
16. Lower the vehicle.
17. Remove the scan tool.
18. Install the tire and wheel assemblies.
19. Inspect the brake fluid level. Refer to Master Cylinder Reservoir Filling.
20. Road test the vehicle while inspecting that the pedal remains high and firm.
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Sunday, March 11th, 2018 AT 12:35 PM
Tiny
BUMPER51
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I mentioned I took the car to a mechanic, he has of course used a scan tool to bleed the lines and it has not solved the problem.
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Tuesday, March 13th, 2018 AT 7:12 AM
Tiny
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There have been times I had to do this several times.

Did you do the manual bleed after the ABS bleeding?

Roy
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Tuesday, March 13th, 2018 AT 7:14 AM
Tiny
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I read your post again and are you sure he used the scan tool to bleed it? Never assume anything. I would call him and verify.

Roy
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Tuesday, March 13th, 2018 AT 7:15 AM
Tiny
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Yes, talked to him yesterday said he did, also tried blocking off rubber brake lines to isolate problem, did not work.
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Tuesday, March 13th, 2018 AT 7:22 AM
Tiny
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Okay, by doing that it either means you still have air in the system or the master cylinder is bad, even though it is a new one.

Roy
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Tuesday, March 13th, 2018 AT 7:23 AM
Tiny
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He has tried two master cylinders.
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Tuesday, March 13th, 2018 AT 7:29 AM
Tiny
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Then you have air trapped in the system. I would use a pressure bleeder to perform this. Gravity and vacuum bleeding are not strong enough.

Roy
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Tuesday, March 13th, 2018 AT 7:34 AM
Tiny
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I will tell him, but I would guess he has tried that also, this has been going on for almost two months.
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Tuesday, March 13th, 2018 AT 7:38 AM
Tiny
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Thats a long time. It sounds like you need another shop that is familiar with bleeding these systems.

Roy
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Tuesday, March 13th, 2018 AT 7:40 AM
Tiny
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You could be right, but this is a very reputable shop, the owner has done nothing but fix cars for close to fifty years. He works on it when things are slow, to try and on labor.
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Tuesday, March 13th, 2018 AT 8:09 AM
Tiny
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I understand but I think you need a second opinion here.

Roy
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Tuesday, March 13th, 2018 AT 8:12 AM

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