Code Definition

P0504 — Brake Switch A/B Correlation

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0504

P0504 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0504 is stored, the module has detected a correlation fault — two sensors that should track each other have diverged beyond tolerance.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0504 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The P0504 fault code is set when the Engine Control Module (ECM) detects a discrepancy or lack of correlation between the signals from Brake Switch A and Brake Switch B. Modern vehicles often use two separate brake switch circuits (A and B) as a safety feature. These switches are activated when the brake pedal is pressed and are used for various functions, including disengaging the cruise control, activating brake lights, and assisting with the anti lock braking system (ABS) and electronic stability control (ESC) systems. The ECM expects these two switches to operate in a correlated manner. If...

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