2017 Tahoe - Brake pedal to floor - Once

[bchandler02]

Hoping someone here can give some ideas. I'm not a GM guy but a family member has a 2017 Tahoe. Last week, after driving the highway for about 30 mins, then city streets for 10-15, they turned into a parking spot. When they did and hit the brakes to stop, the pedal went to the floor and it barely had any braking power. It has < 50k miles on it.

Truck was towed back home and by the time it got back, everything was fine. Had a local shop look everything over and they couldn't find any issue. Also talked to a GM dealer and they had no idea as well.

So far, nobody can explain why this ay happened only once. My first instinct would have been a failed master cylinder, but that would not explain why everything has been fine since.

Anyone have any experience with this or ideas?

 

[swathdiver]

Hoping someone here can give some ideas. I'm not a GM guy but a family member has a 2017 Tahoe. Last week, after driving the highway for about 30 mins, then city streets for 10-15, they turned into a parking spot. When they did and hit the brakes to stop, the pedal went to the floor and it barely had any braking power. It has < 50k miles on it.

Truck was towed back home and by the time it got back, everything was fine. Had a local shop look everything over and they couldn't find any issue. Also talked to a GM dealer and they had no idea as well.

So far, nobody can explain why this ay happened only once. My first instinct would have been a failed master cylinder, but that would not explain why everything has been fine since.

Anyone have any experience with this or ideas?

Fluid level low? Possibly something screwy with the ABS pump that later worked itself out? Have you had them hold the brakes and see if more pressure is needed, the Tahoe starts creeping forward, ala master cylinder going bad anyway? Bump this again in the morning after most of the guys have woken up and had a cup of joe.

 

[bchandler02]

Fluid level low? Possibly something screwy with the ABS pump that later worked itself out? Have you had them hold the brakes and see if more pressure is needed, the Tahoe starts creeping forward, ala master cylinder going bad anyway? Bump this again in the morning after most of the guys have woken up and had a cup of joe.

Fluid level is fine and fluid looks normal.
By holding the brakes, you are saying basically to sit on them as if you are at a red light and see if they hold for a longer period at the same pressure level? Suggestions on how long to test?
Thanks!

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot personally help you with your question; however, other members on this Forum that are much more knowledgeable than me will chime in.

 

[Bill 1960]

Any signs of a hot caliper? A sticky caliper can overheat and boil the brake fluid. Vapor in the system causes that symptom until it cools.

Master cylinder malfunction possibly…

Has it been driven for long distance at high speed since the episode? I would do that and check temp on all 4 brakes with an infrared gun to compare.

If it were mine I would keep after it and not rest until it was found and fixed. Something like this can cause a serious accident.

 

[swathdiver]

By holding the brakes, you are saying basically to sit on them as if you are at a red light and see if they hold for a longer period at the same pressure level? Suggestions on how long to test?

Yes. About as long as your average traffic light, 2 minutes maybe? Not sure if there's an exact amount of time.

 

[bchandler02]

Any signs of a hot caliper? A sticky caliper can overheat and boil the brake fluid. Vapor in the system causes that symptom until it cools.

Master cylinder malfunction possibly…

Has it been driven for long distance at high speed since the episode? I would do that and check temp on all 4 brakes with an infrared gun to compare.

If it were mine I would keep after it and not rest until it was found and fixed. Something like this can cause a serious accident.

So far, no. However, I have suggested they do some driving and then check temps as this theory makes the most sense.
Any ideas how to test for an intermittent master cylinder, aside from just throwing parts at it?

Completely agree. They are hesitant to drive it again without knowing it is resolved.

Yes. About as long as your average traffic light, 2 minutes maybe? Not sure if there's an exact amount of time.

Cool. Will suggest they try that.

 

[iamdub]

Hoping someone here can give some ideas. I'm not a GM guy but a family member has a 2017 Tahoe. Last week, after driving the highway for about 30 mins, then city streets for 10-15, they turned into a parking spot. When they did and hit the brakes to stop, the pedal went to the floor and it barely had any braking power. It has < 50k miles on it.

Truck was towed back home and by the time it got back, everything was fine. Had a local shop look everything over and they couldn't find any issue. Also talked to a GM dealer and they had no idea as well.

So far, nobody can explain why this ay happened only once. My first instinct would have been a failed master cylinder, but that would not explain why everything has been fine since.

Anyone have any experience with this or ideas?

On more than one occasion, I've heard of the GMT800s (and maybe '900s) having an issue where, IIRC, a faulty wheel speed sensor would cause the ABS to trigger unnecessarily. This really sounds like what happened to that '17. It'd be nice if ABS events were stored in memory. Or have the shop live-monitor the ABS to look for irregularities.

 

[Doubeleive]

Hoping someone here can give some ideas. I'm not a GM guy but a family member has a 2017 Tahoe. Last week, after driving the highway for about 30 mins, then city streets for 10-15, they turned into a parking spot. When they did and hit the brakes to stop, the pedal went to the floor and it barely had any braking power. It has < 50k miles on it.

Truck was towed back home and by the time it got back, everything was fine. Had a local shop look everything over and they couldn't find any issue. Also talked to a GM dealer and they had no idea as well.

So far, nobody can explain why this ay happened only once. My first instinct would have been a failed master cylinder, but that would not explain why everything has been fine since.

Anyone have any experience with this or ideas?

there is recall for some of the k2's for the vacuum pump's (leaking) and/or software, one of the symptoms is low braking power at low speed/idle, my 18 had the software updated due to the recall, makes me wonder why the dealer said they couldn't find anything it's well documented. there is a chance perhaps that the vehicle was not in the recall (vin list) but could still be affected, one possible cause for sure is the vacuum pump.

https://gmauthority.com/blog/2020/03/lawsuit-filed-over-alleged-brake-booster-problem-in-general-motors-trucks-and-suvs/

 

[bchandler02]

On more than one occasion, I've heard of the GMT800s (and maybe '900s) having an issue where, IIRC, a faulty wheel speed sensor would cause the ABS to trigger unnecessarily. This really sounds like what happened to that '17. It'd be nice if ABS events were stored in memory. Or have the shop live-monitor the ABS to look for irregularities.

Is there any way to troubleshoot/diagnose this?

there is recall for some of the k2's for the vacuum pump's (leaking) and/or software, one of the symptoms is low braking power at low speed/idle, my 18 had the software updated due to the recall, makes me wonder why the dealer said they couldn't find anything it's well documented. there is a chance perhaps that the vehicle was not in the recall (vin list) but could still be affected, one possible cause for sure is the vacuum pump.

https://gmauthority.com/blog/2020/03/lawsuit-filed-over-alleged-brake-booster-problem-in-general-motors-trucks-and-suvs/

I did see that when searching. However, it seemed like the symptom was that the pedal would be harder to push (due to less vacuum) - this was the opposite. It was very easy to push all the way to the floor.