Start the engine the brake pedal goes to the floor

Tiny
MELANIERC1225
  • MEMBER
  • 2001 GMC YUKON
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 178,000 MILES
My husband replaced all the brake lines, bled the master cylinder, bled the brakes several times. When the car is off the pedal is hard. As soon as you start the engine the pedal goes to the floor. What could be the problem?
Monday, May 6th, 2019 AT 6:10 AM

3 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning,

There is air still in the system. There is a brake bleeding procedure for the ABS module which requires a scan tool for this procedure.

On the scan tool in the brakes section, there will be an automated brake procedure that must be performed. There can be no ABS codes active or the procedure will not run.

Normal bleeding procedures can be used to bleed the individual brake lines provided no air has entered the ABS modulator. But if air has entered the modulator, the system will have to be bled using a pressure bleeder and scan tool:
1. Connect the pressure bleeder to the master cylinder reservoir.

2. Turn the ignition on.

3. With bleeder screws closed, pressurize the system to 35 psi.

4. Select the “Automatic Bleed Procedure” on the scan tool. The scan tool will then energize and cycle the ABS solenoids in the BPMV for one minute.

After this, the scan tool will instruct you to bleed each wheel. During this step, the pump runs and the respective release valve cycles for one minute. This is repeated for each wheel. Finally, the scan tool performs a final 20 second cycling of the ABS solenoids to purge any remaining air.

5. Relieve pressure at the bleed tool and remove it from the master cylinder. Then check pedal height and feel to make sure all the air has been removed and the pedal is firm.

Roy
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Thursday, March 11th, 2021 AT 1:21 PM
Tiny
MELANIERC1225
  • MEMBER
  • 2 POSTS
Thank you so much, I hope this help.
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Thursday, March 11th, 2021 AT 1:21 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
You are welcome.

Always glad to help.

Roy
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Thursday, March 11th, 2021 AT 1:21 PM

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