Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that the car's computer is getting confusing signals from the brake pedal. It's like when you press a button and it doesn't do what you expect.
The car's computer monitors two brake switch signals (A and B) to ensure they are working correctly. If the signals don't match or are out of sync, the P0504 code is triggered.
The P0504 code indicates a discrepancy between the signals from Brake Switch A and Brake Switch B. These switches are part of the brake pedal assembly and are used to inform the engine control module (ECM) when the brake pedal is pressed. If the ECM detects that the signals from these switches do not correlate as expected, it sets the P0504 code.
• Brake lights not working
• Cruise control not engaging
• ABS warning light on
• Check engine light on
• Faulty brake light switch
• Misadjusted brake switch
• Wiring issues or poor connections
• Faulty ECM
ECM: Engine Control Module
OBD-II: On-Board Diagnostics, Second Generation
• Check brake lights operation
• Inspect brake switch and its adjustment
• Test wiring and connections to the brake switch
• Scan for additional trouble codes
• Replace faulty brake light switch
• Adjust brake switch position
• Repair or replace damaged wiring
• Replace ECM if necessary
• OBD-II scanner
• Multimeter
• Screwdriver set
$50 - $200
Moderate
• Toyota Camry
• Honda Accord
• Ford F-150
• Regularly check brake light operation
• Ensure proper brake switch adjustment
• Inspect wiring for wear and tear
Sensor Issue
• Avoid using cruise control until the issue is fixed
• Have the brake system inspected by a professional
Repairs may be covered under the vehicle's basic warranty if the vehicle is still under warranty.
This code has been commonly reported in vehicles with electronic brake systems, especially as vehicles age and components wear.
Moderate – While the vehicle may still be drivable, brake light issues can pose a safety risk.
Driving with malfunctioning brake lights can result in accidents and legal penalties.
• Vehicle ignition on
• Brake pedal pressed
The brake switch is typically located near the brake pedal assembly.
Q: Can I drive with a P0504 code?
A: It's not recommended to drive with this code active, as it may affect brake light operation and cruise control functionality.
Q: How do I reset the P0504 code?
A: After repairs, use an OBD-II scanner to clear the code. If the issue is resolved, the code should not return.
Pro · Four-system diagnostics
A handheld scanner aimed at engine, transmission, ABS, and airbag diagnostic work.
Chassis and ABS faults usually need a scanner that can read brake-system data directly.
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