No brakes.

[Denalibro76]

Afternoon all, I have an 03 Yukon Denali (Hydroboost) and last night I had to hit the brakes hard. When I got home the brake pedal went to the floor accompanied by the service brake system and service stability system messages. No fluid leaking. Any ideas where to start?

 

[blondie70]

Sounds like master cylinder possibly ??

 

[Joseph Garcia]

^^^^x2^^^^

 

[OR VietVet]

If you unbolt the master cylinder from the booster, you can check to see if it is leaking/wet there, at back of master cylinder. If is, that is a sign of a leaking master cylinder. If you replace the master cylinder, make sure to have a qualified tech do it or check here for needed bleeding info. You also could have a line/hose/connection as a problem. You said "no fluid leaking". Where did you check? Just looked on the ground?

 

[Denalibro76]

If you unbolt the master cylinder from the booster, you can check to see if it is leaking/wet there, at back of master cylinder. If is, that is a sign of a leaking master cylinder. If you replace the master cylinder, make sure to have a qualified tech do it or check here for needed bleeding info. You also could have a line/hose/connection as a problem. You said "no fluid leaking". Where did you check? Just looked on the ground?

Yeah. Checked all 4 corners. Fluid level was good as well. The brake pedal is not like a limp noodle…still a tiny bit of pressure on the way down.

 

[OR VietVet]

Yeah. Checked all 4 corners. Fluid level was good as well. The brake pedal is not like a limp noodle…still a tiny bit of pressure on the way down.

Sounds like bypassing internally in the master cylinder.