P0504: Brake Switch "A"/"B" Correlation
Modern vehicles use two redundant brake switch signals (often one normally-open and one normally-closed). When the two signals disagree, this code is set; common causes include a misadjusted switch, internal switch failure, or wiring fault.
What P0504 means
P0504 is a generic OBD-II powertrain code in the speed, idle & cruise group.
- Check engine light
- Usually on
- Emissions-related
- No
- Limp mode possible
- Not typical
- Drive cycle to clear
- Not required
Get it fixed
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Common causes
- 01Brake switch misadjustedMost likely
- 02Brake switch internal faultPossible
Can I drive with P0504?
Usually yes, for a short time.
The car will often drive normally, but get it diagnosed soon. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
Why we rate it moderate
- Turns on the check engine light
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose P0504
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just P0504. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Fix other faults first
If other codes are stored, start with power-supply, sensor-circuit and communication codes. They can cause this code as a side effect.
- 3
Check live data
Watch the related sensor and actuator readings in live data (Brake light switch, Brake switch wiring) and compare them with expected values in the service information for your vehicle.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Brake switch misadjusted; brake switch internal fault. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and drive the car under the conditions in the freeze-frame data to confirm it does not return.
P0504 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Easy
- Good DIY job?
- Yes, with a scan tool
Basic hand tools; a common first DIY job.
Parts and systems involved
- Brake light switch
- Brake switch wiring
P0504 FAQ
What does P0504 mean?
P0504 means “Brake Switch A/B Correlation”. Modern vehicles use two redundant brake switch signals (often one normally-open and one normally-closed). When the two signals disagree, this code is set; common causes include a misadjusted switch, internal switch failure, or wiring fault.
Is P0504 serious? Can I keep driving?
We rate P0504 as moderate severity. Usually yes, for a short time. The car will often drive normally, but get it diagnosed soon. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
What causes P0504?
The most common causes, from most to least likely: Brake switch misadjusted; Brake switch internal fault. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix P0504?
Typical labor is about $25–$125 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix P0504 myself?
DIY difficulty is easy. Many owners can handle it with a scan tool, a multimeter and basic hand tools. Always confirm the cause before buying parts.
Will P0504 clear itself?
If the fault was intermittent, the warning may go off once the computer stops seeing it, but the code stays in memory. Fix the cause; clearing the code alone doesn’t repair anything.