P0504 code meaning
Brake Switch A/B Correlation
What P0504 means
The brake pedal switch has two contacts – A usually for the brake lights, B for cruise control and brake information – working in opposite sense, so the module expects opposite states on every brake application. P0504 means they disagree. The signal is used for cruise control cut-off, brake override with electronic throttle, the shift interlock and start-stop. Ford sets it only after more than 25 (gasoline) or 40 (diesel) disagreeing brake applications, with the wrench lamp instead of the warning lamp; a NHTSA investigation covers Hyundai brake light switches.
P0504 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyEasy, DIY possible
- Typical labor0.2 to 1 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0504
- Cruise control cannot be switched on
- Brake lights stay on or do not come on
- Selector lever cannot be moved out of P
- Wrench or ESC lamp on
Common causes of P0504
- Most likelyBrake light switch faulty (burnt or corroded contact)
- Most likelySwitch misadjusted or retaining clip or stop pad worn
- PossibleWire, connector or brake light fuse faulty
- Less likelyMoisture in fuse or junction boxes
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Brake pedal switchBrake light circuitEngine control module
What each part of P0504 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| 04 | The exact fault in that area. |
What to do next
- Note P0504 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0504
What does P0504 mean?
P0504 means "Brake Switch A/B Correlation". The brake pedal switch has two contacts – A usually for the brake lights, B for cruise control and brake information – working in opposite sense, so the module expects opposite states on every brake application. It is a generic code, so it means the same on every make.
Is it safe to drive with P0504?
Drive gently and only to a workshop. With P0504 the car can go into limp mode (reduced power) to protect itself.
Will P0504 fail an emissions test?
P0504 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P0504 to fix?
Difficulty: easy. A typical repair takes 0.2 to 1 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0504 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.