P0504 on Ford
Brake Switch "A"/"B" Correlation
P0504 on Ford vehicles indicates brake switch "a"/"b" correlation. Au7o has documented this code across 1 Ford model — most commonly on Mustang. Most vehicles use two independent brake switch signals (a normally-open and a normally-closed circuit, switch A and switch B). The PCM compares them and expects them to change state together when the brake pedal is pressed. P0504 sets when the two signals disagree (do not correlate), indicating one switch or circuit is faulty. Typical repair costs on Ford range from $2 to $250, depending on the specific model and root cause.
Common Causes of P0504
- •Failed brake light switch
- •Misadjusted brake switch (plunger gap)
- •Wiring/connector fault on one of the two brake switch circuits
- •Blown brake-circuit fuse affecting one signal
- •Faulty PCM input
P0504 on Ford by Model
Ford Mustang(1 issue)
- Brake Pedal Bumper Failure Causing Limp Mode and Battery Drain2015-2023
A small plastic clip called the brake pedal bumper/stopper can break and fall out of position, causing the brake light switch to remain constantly engaged. This results in brake lights staying on even when the pedal is released (including when the car is off, draining the battery), the engine going into limp mode limiting RPM to around 2,000, and transmission shifting issues.
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View P0504 across all makes →Frequently Asked Questions
What does P0504 mean on Ford?▼
P0504 stands for "Brake Switch "A"/"B" Correlation." Most vehicles use two independent brake switch signals (a normally-open and a normally-closed circuit, switch A and switch B). The PCM compares them and expects them to change state together when the brake pedal is pressed. P0504 sets when the two signals disagree (do not correlate), indicating one switch or circuit is faulty. On Ford specifically, this code is documented across 1 model.
What causes P0504 on Ford vehicles?▼
Common causes on Ford: Failed brake light switch, Misadjusted brake switch (plunger gap), Wiring/connector fault on one of the two brake switch circuits, Blown brake-circuit fuse affecting one signal, Faulty PCM input. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0504 on a Ford?▼
Repair costs on Ford range from $2 to $250, depending on the specific model and root cause.
Which Ford models have P0504 documented?▼
Au7o has documented P0504 on 1 Ford model: Mustang.