DTC P0504-27: Brake Switch A F/B Correlation - Signal rate of change above threshold: Action

Check for related brake pressure DTCs within the anti-lock braking control module
Check brake pedal switch is fitted correctly. Clear DTC, start the engine and press the brake pedal, using maximum travel, for greater than 1 minute taking care not to press the accelerator pedal
Check and install new brake pedal switch as required