P0504Generic code

P0504 Code: Brake Switch A/B Correlation

The P0504 code indicates that the two signals from the brake pedal switch do not agree. It is usually caused by the switch itself, its adjustment or the rubber pedal stop. Cruise control stops working while the code is active.

Severity
Medium
Can I keep driving?
Yes, but with caution
Estimated cost
$15 to $150
Difficulty
Easy
System
Idle and Speed Control
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0504 code means

Many brake switches have two contacts. One closes when you press the pedal (brake lights), and the other opens when you press it (cruise control and the computer). The computer expects them to always be in opposite states. If they match for a period of time, it stores the P0504 code.

It is a very common and inexpensive fault. The switch wears out or goes out of adjustment, or the rubber stop on the pedal falls off and leaves the switch halfway through its travel. A blown brake light fuse can also cause it.

While the code is active, cruise control does not work and, on some vehicles, the automatic shift lever will not leave Park or the engine will not start with the push button.

P0504 code symptoms

  • Cruise control that does not work.
  • Brake lights that do not come on or stay on.
  • The shift lever will not leave Park (some vehicles).
  • Check engine light on.

Likely causes of the P0504 code

  1. Brake switch worn or out of adjustment. The most frequent cause.
  2. Rubber pedal stop fallen off, so the switch sits halfway through its travel.
  3. Blown brake light fuse, which leaves one of the two contacts without a signal.
  4. Switch connector damaged by the movement of the pedal.

How to diagnose the P0504 code step by step

  1. Watch the state of both signals on the scan tool as you press and release the pedal. They should change at the same time and in opposite directions.
  2. Check the rubber stop on the pedal.
  3. Check the brake lights.
  4. Measure continuity of both contacts in both positions.

How to fix the P0504 code

  • Replace or adjust the switch.
  • Replace the rubber stop.
  • Replace the fuse if it is blown.
  • Clear the code and check the cruise control.

Technical reference data

  • One normally open contact (lights) and one normally closed contact (cruise control and computer).
  • Approximate values only: check the manufacturer data for your vehicle.

Brand-specific notes

This fault is very frequent on several makes, and some models had service campaigns for it.

P0504 on Hyundai

Very frequent on Hyundai vehicles.

P0504 on Kia

Very frequent on Kia vehicles.

P0504 on Ford

Very frequent on Ford vehicles.

P0504 on GM

Very frequent on GM vehicles.

Frequently asked questions about P0504

Can I drive with a P0504 code?
Yes, but check that the brake lights work. A P0504 code can come from a switch that also controls them, and the drivers behind you depend on them.
Why does my cruise control not work?
Because the computer cannot know for sure whether you are braking, so it keeps the cruise control disabled.
Is it expensive?
No. The switch is usually cheap.
How much does it cost to fix P0504?
Roughly $15 to $150, depending on whether it is a fuse, a rubber stop or the switch.
What does the P0504 code mean?
It is a generic OBD2 code that means the two signals from the brake pedal switch do not agree. They should always be in opposite states.
What is the most common cause of P0504?
A worn or misadjusted brake switch. A fallen rubber pedal stop and a blown brake light fuse are close behind.

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