Brake pedal does nothing

[shovenose]

Was driving on the highway and went to brake and pedal went down but envoy did not stop or barely even slow down. Pumped it a few times and it came back. That happened twice more during the trip. When it didn't happen brakes were good. Fluid level seemed fine, no obvious leaks. Any ideas? Thanks

 

[littleblazer]

Failing master? If you pumped it and it came back it's bleeding somewhere. Maybe dropping pressure in the abs module?

 

[Mooseman]

I'd also suspect the master. Not too expensive and easy replacement except for bleeding all four corners.

Try cracking open the bleeder open and pumping the brake as if bleeding it. I just did the same on a G6 that had a partially failed master. No fluid coming out of one caliper.

 

[AWD V8]

If the pedal "felt" the same, as in the same firmness, didn't drop to the floor, I doubt it was the master. A "normal" feeling pedal would mean that the master is making and holding pressure.

I'd suspect an ABS issue. The ABS has the ability to cut off fluid to any wheels it deems necessary. If the ABS module is getting some bad data, say from a wheel sensor, it may act on that and cut off, or reduce the fluid to that wheel.

I've seen the ABS both cut off fluid to the wheels, or not allow the fluid to return after a brake application, keeping the brakes applied.

I'd try removing the ABS fuse first and seeing if that makes a difference, then go from there.

 

[shovenose]

i have had a code for long time issue with transmission/rear abs speed sensor. it never seemed to do anything besides an intermittent jumpy speed reading between like 0 and 20. could this cause it?

and no, the pedal didn't not feel the same. it was a lot less resistance, i would say it just sank to the floor, but not quite...

 

[jsheahawk]

i have had a code for long time issue with transmission/rear abs speed sensor. it never seemed to do anything besides an intermittent jumpy speed reading between like 0 and 20. could this cause it?

and no, the pedal didn't not feel the same. it was a lot less resistance, i would say it just sank to the floor, but not quite...

Yes, it could. That's a pretty easy fix.

 

[Mooseman]

If the pedal "felt" the same, as in the same firmness, didn't drop to the floor, I doubt it was the master. A "normal" feeling pedal would mean that the master is making and holding pressure.

The G6 I just worked on also felt "normal". However, it does not have ABS so that could be a possible issue in this case. Only way to confirm one or the other is to crack open each line in and out at the ABS module and watch for fluid coming out of each corresponding line.

And he did mention that the pedal went to the floor during the "no brakes" situation.

 

[shovenose]

The plot thickens, drove the vehicle another like 100mi yesterday with no issues - super frustrating. since it's a known problem i'll replace the speed sensor... and it's not abs speed sensor but transmission speed sensor, but this vehicle does not have four speed sensors, it uses the transmission speed sensor as the rear abs sensor.

 

[Njg425]

I had the same issue start about two years ago (other than the brakes intermittently not working). I replaced the rear speed sensor and it didn't do anything to help and the code remains to this day. I'm interested to see if you come up with a solution since I was unable to.

 

[shovenose]

I had the same issue start about two years ago (other than the brakes intermittently not working). I replaced the rear speed sensor and it didn't do anything to help and the code remains to this day. I'm interested to see if you come up with a solution since I was unable to.

Later today I'll go to O'Reilly and order the sensor. It's pretty cheap, and I'll update once it's installed. I also ordered in a master but IDK if I want to change that right now.

 

[Tiggerr]

The plot thickens, drove the vehicle another like 100mi yesterday with no issues - super frustrating. since it's a known problem i'll replace the speed sensor... and it's not abs speed sensor but transmission speed sensor, but this vehicle does not have four speed sensors, it uses the transmission speed sensor as the rear abs sensor.

If your pedal "went to the floor" I would not be driving it!
You need a master cylinder..
Especially since you said it "pumped up"
Ive never seen an abs issue cause a pedal to just go to floor like that...