The brake light switch is an input to the BCM - body control module , do you know about BCM'S - electronic module ?
Stop Lamps
When the driver presses the brake pedal, the switch contacts open and battery positive voltage is interrupted to the BCM. The BCM then supplies voltage to both the turn/stop lamp supply voltage circuit and trailer rear turn/stop lamp supply voltage circuits. The BCM also supplies voltage to the CHMSL though a dedicated circuit.
could have DTC'S stored in the BCM
DTC B3445 00: Stop Lamp Circuit
Circuit/System Description
The stop lamp switch is used to sense the action of the driver application of the brake pedal. The body control module (BCM) provides a low reference signal and a B+ reference voltage to the stop lamp switch. When the stop lamp switch contacts close indicating the brakes have been applied, the BCM will apply battery voltage to stop lamp relay control circuit and the center high mounted stop lamp (CHMSL). When the stop lamp relay receives battery voltage from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage to the STOP LAMPS fuse to illuminate the left and right stop lamps.
DTC C0277 00: Brake Pedal Position Sensor Calibration Not Learned
DTC C0297 00: Brake Applied Output Circuit
DTC C0890 00: Device Voltage Reference Output 3 Circuit Voltage Out of Range
In the event that DTC C0277, C0297, or C0890 sets as current in the body control module (BCM) is an indication of a possible internal BCM malfunction or programming error. There are no external circuits available to diagnose on this vehicle with respect to these DTCs.
Your best bet would be to take your vehicle to a qualified repair shop or the Cadillac dealer.
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