P0504: Brake Switch A/B Correlation
Can you still drive? Yes, but verify your brake lights work properly first. If brake lights are stuck on or not working, this is a safety hazard and must be fixed immediately.
What Does P0504 Mean?
Code P0504 indicates that the ECM has detected a disagreement between the two brake light switch inputs. Modern vehicles use redundant brake switch circuits for safety. One circuit controls the brake lights while the other signals the ECM for functions like cruise control deactivation and torque converter lockup release. When these signals do not agree, P0504 is set.
Need to read your codes?
An OBD-II scanner lets you read and clear diagnostic trouble codes from your vehicle's computer. Most scanners work with any car made after 1996.
Browse OBD-II Scanners on AmazonCommon Causes
- Misadjusted brake light switch
- Failed brake light switch
- Corroded brake switch connector
- Damaged wiring in brake switch circuit
- Brake pedal bracket or bushing worn allowing excessive pedal play
Symptoms
- Check engine light on
- Cruise control will not engage or stay on
- Brake lights stay on or do not illuminate
- Shift interlock may not release in some vehicles
- Torque converter may not lock up properly
Diagnostic Steps
- 1Check brake light operation (lights on when pedal pressed, off when released)
- 2Monitor both brake switch inputs with scan tool while pressing and releasing pedal
- 3Inspect brake light switch adjustment at the brake pedal bracket
- 4Check brake switch connector for corrosion or loose pins
- 5Test brake switch resistance in both positions
- 6Replace brake light switch if adjustment does not resolve the code
Recommended Parts & Tools
brake light switch
brake pedal bushing
electrical contact cleaner
Estimated Repair Cost
| Type | Estimated Cost |
|---|---|
| Total Repair Cost Range | $20 - $150 |
Get a Personalized AI Diagnostic Report
Get a detailed AI diagnosis for code P0504 specific to your vehicle. Includes step-by-step repair instructions, exact parts needed, and a cost breakdown tailored to your make and model.
Chat with AI About P0504Commonly Affected Vehicles
Related Recalls
1 Active Recall — 2026 Ford F-150
The following NHTSA safety recalls have been issued for this vehicle. Contact your dealer to check if your vehicle is affected.
ELECTRICAL SYSTEM: INTEGRATED TRAILER BRAKE CONTROL
Ford Motor Company (Ford) is recalling certain 2021-2026 F-150, 2022-2026 F-250 SD, F-350 SD, F-450 SD, F-550 SD, Maverick, 2024-2026 Ranger, 2023-2026 F-600 SD, 2022-2027 Lincoln Navigator, Expedition, and 2026 E-Transit vehicles. When towing a trailer, the integrated trailer module (ITRM) may lose communication with the vehicle, possibly causing a loss of brake and turn signal lights, or a loss of brake function. As such, these vehicles fail to comply with the requirements of Federal Motor Vehicle Safety Standard number 108, " Lamps, Reflective Devices, and Associated Equipment."
Remedy: The integrated trailer module software will be updated by a dealer, or through an over-the-air (OTA) update, free of charge. Owner notification letters are expected to be mailed March 17, 2026. Owners may contact Ford customer service at 1-866-436-7332. Ford's number for this recall is 26C10. Vehicle Identification Numbers (VINs) involved in this recall will be searchable on NHTSA.gov beginning March 17, 2026.
Data provided by the National Highway Traffic Safety Administration (NHTSA).
Frequently Asked Questions
Can P0504 cause cruise control to stop working?
Yes, the ECM uses the brake switch input to verify when the brake is released before allowing cruise control to engage. If the signals are inconsistent, cruise control will be disabled as a safety measure.
Is the brake light switch easy to replace?
Yes, the brake light switch is located at the top of the brake pedal and is typically held in by a clip or quarter-turn mount. It is an inexpensive part and takes about 15-30 minutes to replace.
Community Fix Reports
Community reports are user-submitted and not verified by Auto AI Buddy. Results may vary.
Related Codes
Affiliate Disclosure: This page contains affiliate links. If you purchase products through these links, we may earn a small commission at no additional cost to you. This helps us maintain this free resource. We only recommend products we believe will help you diagnose and repair your vehicle. Prices shown are estimates and may vary.