GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hello, my name is ***** ***** I will be assisting you today on your gmc. Have you had it scanned for any dtc codes? Also when you speak of the rough feeling are you talking about a brake shake when applying the brake pedal usually will be noticed when coming off the interstate? I have also seen a few issues with the brake master cylinder leaking into the brake booster which will cause the lights to come on and will also cause the brake pedal to make a squeak noise on apply. You will also notice low fluid, I would also check that. Check the fluid and also there should be a sensor at the bottom of the brake booster below the master cylinder I would reach down and pull that sensor out and see if any fluid runs out if it does then that will be your problem. Let me know what you find after you check those few things.
Did you find the issue with your Gmc? Do you need any further assistance?