In stop and go traffic on highway at low speed experienced brake pedal stiffening and difficulty stopping. Reoccurred several times during same traffic pattern but only at the low stop and go speed. Problem occurred with no warning. Brakes worked as normal under other circumstances. Forum research suggested this was a vacuum pump and occurred to other models of same year and millage. Vacuum pump (internal) failure was confirmed issue by GM dealer and replaced. Mileage when problem occurred was approximately 47,200 miles. Vehicle in good condition, no wrecks, regular maintenance, and not used for towing or heavy hauling.

- Kings Mills, OH, USA

I first noticed the issue on the morning of Saturday, November 10th as I was backing into a parking spot. As I was backing in, I noticed all of a sudden the brake pedal was on the floor and I was about to plow into a curb and threw the truck in park. I didn't think anything of it. The second time it happened was one day later as my fiance and I had just completed a 200 mile drive home. I was pulling into the parking lot at our townhouse complex and as I was pulling forward to back into the space, I noticed I had no braking power whatsoever. I had to throw the truck in park to keep it from hitting a neighbors vehicle. I opened the hood with the engine running, and noticed a ticking noise I hadn't heard before and my brake pedal only had about 1/4" of travel left. I could pull the pedal back to where it is supposed to be but it would just fall back down to the floor. I was able to very slowly and carefully park the truck using park and the parking brake. With the engine still running and the vehicle in park, I depressed what was left of the brake pedal and held it to the floor and heard a moaning noise coming from the area near the master brake cylinder and could feel the brake pedal shuddering under my foot. I feel unsafe driving this vehicle and I was giving no warning of the brake failure. I am having the vehicle towed to sewell Buick GMC in dallas and will update when they find cause. I will also be calling GM customer support as I feel this is a huge safety hazard.

- Dallas, TX, USA

When going under 15mph brake pedal becomes hard and doesn't work. Vehicle has 50K miles. Brake booster declared bad by mechanic. This issue almost casued accident.

- Georgetown, KY, USA

Truck looses braking ability at low speeds such as traffic or parking lots.

- Fairfield, CA, USA

Issue when braking that causes the brake pedal to lose power and causes the driver to depress the pedal extremely hard to have the brakes engage. The cause appears to be a faulty vacuum pump that requires replacement. This could be potentially a large safety issue if the pump fails and the vehicle is unable to be stopped in time to avoid a possible collision. This issue has occurred both while in traffic on a city street and while attempting to park the vehicle.

- Baton Rouge, LA, USA

The vacuum pump controlling the brakes has failed. When the brake is pressed in stop/go traffic, it will first stop the vehicle, but if the brake is released then pressed again, the brakes will not work and the vehicle continues to roll forward. A mechanical/electrical noise can be heard before this occurs. This is more noticeable on wet roads or roads with a steep decline.

- Hixson, TN, USA

At low speeds (parking speed, school pickup lines, creeping traffic speed) the brake pedal will lose all boost pressure. The brake pedal becomes extremely stiff and ineffective. This situation occurred on a few occasions and caused great alarm with myself and my wife. Great potential exists for an accident involving machinery, animals or human beings. The vehicle was taken promptly to the local GMC dealership for service with a copy of GM service bulletinno.: pit5361B. The dealer kept the vehicle for several days to perform an existing safety recall for steering anomalies (recall # 18289) as well as diagnose and repair the brake boost issue. Service bulletin pit5361B was followed and the vacuum pump assembly was replaced to resolve the brake boost issue. This repair occurred at 40728 miles - just beyond warranty coverage terms. Total cost of repair $686.56. The brake boost issue has not reoccurred to date since the repair. This vehicle is not abused or involved in any rigorous activity. It is a general use vehicle and is used primarily for family errands and road trips.

- Aledo, TX, USA

When brakes are applied the pedal is hard and vehicle does not stop. It seems to happen when going slow for example in parking lots etc. I have read other articles where people are experiencing same thing at high and low speeds. It does not happen all the time, but it started 11/2017 and I've experienced this four times now and the wife as well.called GM the other morning was told there was no recall for this issue per GM some vehicles were affected but not mine, explaining what I've found and was told to take the vehicle to dealer for diagnostic.asked if it would have to be the dealer cause they were expensive to do diagnostic. Was told yes and it would have to be out of pocket.

- Horizon City, TX, USA

Vehicle is shutting off at any given speed, ie. 35 mph in town or 70 mph on a highway with oncoming traffic. When vehicle shuts off, loss of all control of the vehicle takes place. No brakes, no steering, nothing until the vehicle randomly turns back on. This is not a consistent occurrence to know when it is going to happen or be prepared for it to happen. I watched my husband shoot across the road into the other lane and almost put the vehicle over a bank one night when it happened. This has been an issue since January 2018 for us, we have taken it to the dealer where it was purchased multiple times for them to tell us they can't duplicate the issue and nothing is coming up in their system for an error code. It has caused a major inconvenience for my family, as we don't dare put our children in the truck leaving the responsibility solely on one parent to Transport the kids to and from daycare. I worry for the safety of my husband on a daily basis.

- Pine City, NY, USA

The contact owns a 2015 GMC Sierra 1500. An independent mechanic called on behalf of the vehicle owner, who is deaf. The contact stated that the brake pedal failed to depress and stop the vehicle properly. The contact diagnosed that the vacuum pump and the brake booster system were malfunctioning. The dealer (gulf coast Chevrolet Buick GMC, 1901 w. fm 523, angleton, tx 77515, (800) 593-5226) stated that there were no recalls on the vehicle. The manufacturer was called and the contact was provided a case number. The manufacturer stated that the vehicle had too many miles to be covered by the extended warranty. The failure mileage was 69,000.

- Houston, TX, USA

Hard brake pedal when attempting to stop, happens on hwy with fast speeds, slow speeds in parking garage and in reverse.

- Chesterfield, MI, USA

While driving at highway speed, I entered an off ramp to find no power assist to my brakes. The pedal was extremely stiff. I came very close to having a collision with the car in front of me. I contacted my mechanic immediately, he checked it out and it appears the vacuum pump has failed without warning. I have owned this vehicle since new and have had no problems with it until this issue.

- Arkansas City, KS, USA

I was backing up and the brake pedal got hard and would not stop the truck. I tried to go forward and the same thing happen.

- Bolivar, MO, USA

Vacuum pump vachose assy brake booster and mastercyclinder failure which cause brake failure while driving. Happened several times until 'service trailer brake' light came on. No brakes, no way to press down pedal. GMC refuses to assume responsibility for repair. Cost: $1311.16

- Mebane, NC, USA

Having issues with hard brake pedal. It happened a few time when the truck was new but could never duplicate it. Twice it almost caused an accident. I have since found a way to duplicate it. When backing a boat trailer down a ramp every time they become hard, I have to ride the emergency brake, but it only happens when the boat is on the trailer. I have researched this over the years but not till recently have I seen other reports of truck with this issue. I have not contacted the dealer yet but will in the next week or so when I can take off to go. I do not now date of first occurrence but I put a random date in 2015.

- Robert, LA, USA

The contact owns a 2015 GMC Sierra 1500. The contact stated that the vehicle failed to pass state inspection due to master cylinder, vacuum pump, brake booster, and hose leakage. The dealer was not contacted. The manufacturer was notified of the failures. The vehicle was not repaired. The failure mileage was approximately 33,000.

- West Kennebunk, ME, USA

When brakes are applied the pedal is hard and vehicle does not stop. It seems to happen when going slow for example in parking lots etc. I have read other articles where people are experiencing same thing at high speeds. It does not happen all the time, but it started 7/1/2018 and I've experienced this four times now. Took to dealer this morning they refused to look at articles explaining what I've found.

- Hendersonville, TN, USA

While in motion the brake pedal goes hard and is difficult to stop. I believe this is the cause of a low speed incident I had earlier this year. The issue occurres mostly at slow speeds in stop and go traffic. If feels like the brake booster fails and the pedal is bottomed out. It happens frequesntly while hauling a trailer in reverse. Very dangerous situation.

- Harrison Township, MI, USA

Brake failure due to bad vacuum pump

- Darien, CT, USA

While driving in stop and go traffic speeds there have been a number of occasions that the brake pedal goes hard and the truck will not stop. I have noticed on other forums that this seems to be a common issue.

- Rocky River, OH, USA