2011 gmc sierra slt brake warning light on dash

[Mandalorian gmc]

Brake warning light came on the other day. The light was off the next day then came back on when i drove it again. I unplugged the connection on the switch and that did stop it for abit then the light and chime came back on and now i am lost. other things I have done are- I checked the e brake and it was not on. also checked the brake fluid and topped it off checked that sensor. Also have replaced the ebrake switch. Checked all my brake lights and replaced some bulbs in the rear exterior cab light. Had a look at the brakes and they shouldn't be causing it they will probably need to be done in the next year tho. All the cables for ebrake are good also. Also no notifications on message center. Had a friend run his code reager on it but nothing showed up. If anyone has any other ideas it would be greatly appreciated. Thanks

[Doug_Scott]

The light can come on for a couple of reasons. Pressure differential is the most important reason. Try putting the truck in drive while idling, and just put enough pressure on the brake pedal to keep the truck stationary. The key to this test is to only apply the least pressure possible. Watch for the brake pedal slowly sinking away from your foot. If the pedal slowly sinks to the floor during this test, try it again, but this time apply more pressure. If it does not drop with more pressure, then the issue is likely the master cylinder.