Error code

OBD2 P0504

OBD2P0504
Diagnostic Trouble Code· Standard OBD-II fault code read from the vehicle's onboard diagnostics.

What it means

Brake Switch 'A'/'B' Correlation.

Severity

severeDo not drive the vehicle until this issue is resolved to avoid a possible crash.

Summary

P0504 indicates an issue with the brake switch 'A'/'B' correlation, meaning there's a problem with how the brake light circuit interacts with other systems like cruise control or shift interlock safety systems.

Symptoms

  • Stored trouble code and possibly an illuminated warning light
  • Brake lights may be on permanently or fail to illuminate
  • Gear selector may be impossible to move out of 'P' or 'N'
  • Cruise control system may not activate or fail to deactivate

Common Causes

  • Defective brake light switch (most common)
  • Damaged, burnt, shorted, disconnected, or corroded wiring/connectors
  • Blown fuses/fusible links
  • Failed PCM (rare)

Diagnosis

  1. Record all fault codes and freeze frame data.
  2. Check brake light switch for proper operation and adjust if necessary.
  3. Inspect wiring, connectors, fuses, and bulbs in the brake light circuit.
  4. Test associated systems like cruise control or shift interlock safety systems.

Fixes

  • Replace defective brake light switch

FAQ

What should I do if the code persists after replacing the brake light switch?

Refer to the manual for testing procedures of associated circuits/systems or take the vehicle to a professional repair facility.

Is it safe to drive with P0504?

No, driving is not recommended until the issue is resolved as it poses a serious risk to life and limb.

View source

Not affiliated with OBD2. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.

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