P0504 means Brake Switch A/B Correlation. The two circuits in the brake light switch disagree: one says the pedal is pressed and the other says it is not. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0504 means
Most engine sensors receive a 5-volt reference and return a signal between roughly 0 and 5 volts. Codes ending in circuit high or circuit low usually point to an electrical fault: an open circuit, a short or an unplugged connector. Range/performance codes mean a signal is present but disagrees with what the computer expects from the other sensors, which more often points to a dirty sensor, an air leak or a mechanical problem.
P0504 symptoms
- Cruise control not working
- Brake lights stuck on or not working
- Shifter will not leave park on some vehicles
- Push-button start not responding on some vehicles
Common causes of P0504
- Misadjusted brake switch
- Failed brake switch
- Broken pedal stop bumper
- Wiring fault
How to diagnose P0504
- Check brake light operation
- Watch both switch inputs on a scan tool as you press the pedal
- Check switch adjustment and the pedal bumper
Can you drive with P0504?
Make sure the brake lights work before driving.
P0504 tips
A broken plastic stop bumper on the brake pedal arm is a common cause of brake switch codes; check it before replacing the switch.
Will P0504 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0504 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0571 | Brake Switch A Circuit |
| P0703 | Brake Switch B Input Circuit |
| P0500 | Vehicle Speed Sensor A Malfunction |
Guides that help
When it is more than a sensor
Sensor codes are usually fixed with a sensor, a connector, wiring or a leak repair rather than major parts. If testing turns up internal engine trouble instead, see how to tell if an engine is blown and compare engines by code on our engines page.
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