I have a 2011 Audi A4 quattro manual transmission. I recently got a red BRAKE light on my dash. It started about a week ago in a different manner from how it is now. At first I was driving on the freeway and it came on with a beep and turned off 5 seconds later. It did that one other time. I trouble shot the light and checked my brake fluid. It was at the minimum capacity so I filled it. Later that week I changed the rear brake pads in rotors thinking that it may be that the brake pads were too worn. They were due for changing anyway. The front brakes had been serviced by myself months ago. Now, the brake light is turning on as soon as I start my car. It beeps 3 times and doesn't turn off now. My brakes feel fine, the brake pads are new on all 4 wheels. the brake fluid is filled and staying at a steady level, the brake lights are all good. Any ideas?

 

Usually it means the brake pad sensor is contacting the rotor. But I did a little googling...
Common FailuresSometimes, the brake pad warning light will come on when the pads have the majority of the friction material present. This stems from issues with the circuit’s integrity. The most likely culprits are the connectors in the wheel wells.

Water can enter into the brake pad’s wear sensor connector and change the resistance in the circuit. The change in resistance caused by the oxidation of the connector pins causes the light in the instrument cluster to illuminate. The customer may report that the problem is intermittent, with the light going out once the connector has dried out during the next ignition cycle. The connector can be cleaned with electrical contact cleaner and sealed with dielectric grease. This tends to occur on vehicles with removable wear sensors that are not replaced along with the brake pads.

The other failure is the ground for the circuit. Using the wiring diagram, find the ground point on the chassis and test the continuity of the circuit from that point, and also test the connection at the sensor.

Another common mistake is not securing the wiring harness for the sensor to the clips on the knuckle, strut and control arm. The wires can be damaged by the rotating axle or the constantly moving suspension..

You have the same 2011 MT6 as I do, with electric parking brakes. It might be related to this when you replaced the rear brake pads...
Detecting Rear PAD Wear
If you are working on an Audi model with an electric parking brake that is either equipped with motors on the calipers, or a motor that pulls the parking cables, these systems can measure the thickness of the pads. They calculated the thickness of the pads by counting the turns of the electric motor to determine their thickness. But, most systems also have wear sensors. The position sensor and motor are also used to retract the pads to reduce drag.

The system will perform the check at a distance set by Audi, which is typically 1,000 km when the vehicle is turned off. The customer might hear the motors at the calipers working when the car is parked in the garage. This is normal and the customer should not be concerned.

It is critical that a scan tool is used to retract the caliper’s piston and adjust the pads after the rear brake pads are replaced. If this step is not performed, the brake and brake pad light can come on together.

 

Which also means you are likely due for new pads. On Infinitis, the Slip and VDC lights will come on as well. Most people complain that it happens intermittently. It happens when accelerating, deccelerating, or going up or downhill. It's because the fluid gets sloshed around and the sensor doesnt pick it up for a Tutuapp 9Apps Showbox second