If you were pressing on the brake pedal when releasing the parking brake, the pedal most likely went down further and activated the Low Pressure Switch.
If you do not have any codes, but still have a brake warning, it is possible the low pressure switch has been activated. There are three switches in the brake circuit. 1. Brake light switch, 2. Hydraulic pressure switch, and 3. Low pressure switch (this is really a limit switch that just senses the pedal has traveled too far). This can be reset by the following procedure.
After a low pressure switch (LPS) problem has
been solved, it is necessary to clear the occurred
fault in the VCM as fo llows:
1. Turn ignition switch OFF.
2. Wait 30 seconds.
3. Turn ignition switch ON.
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4. Firmly press brake pedal until you hear a "click"
from the LPS sw itch or until braking pressure
reaches 3 500 kPa (508 PSI) .
NOTE: The 1st click will come from the brake light
switch. Continue to strongly press pedal to hear
a 2 nd click. This one will come from the low pressure
switch. You may not hear the click, just push the pedal real hard.
5. Turn ignition switch OFF.
6. Wait 30 seconds.
7. Turn ignition switch ON.
8. Validate fault was cleared.
When I say press the brake pedal down, I mean do it really HARD!