P0504: Brake-switch correlation is accumulated across braking events

P0504 identifies disagreement between brake-switch A and B in Ford’s diesel example. The source describes one switch indicating pressed while the other indicates not pressed, accumulated over 40 braking events. This is a correlation assessment across operating events rather than a single universal voltage reading.

Disagreement differs from missing activation

The same section separates P0572, where expected brake activation is absent across inferred braking events, and P0573, where activation appears during inferred acceleration events. Those comparisons use different evidence from P0504’s disagreement between the two switch states.

Monitoring is continuous, but the duration varies with driving conditions. Forty events are not equivalent to a fixed number of seconds or one long pedal application. A single matching pair of states cannot erase the earlier accumulated disagreement.

Preserve both states and the event context

Record the complete code, both available switch states and the circumstances of the discrepancy. The summary does not publish a universal switch-adjustment setting, connector pin or acceptance voltage for this correlation check.

A correlation fault does not by itself identify which switch, circuit or interpreted state is incorrect. Verification must follow the applicable brake-switch procedure while maintaining normal brake safety. It does not justify bypassing either input or deliberately driving through repeated abnormal braking events simply to reach the source’s diagnostic count.

Source and applicability

Ford 2023–2024 diesel OBD summary, August 25, 2023 revision; only the described monitor examples. Confirm the engine and calibration before applying values. The monitor explanation does not identify a failed part or replace the applicable service procedure. Ford PDF, page 97.