P0504

Brake Switch A/B Correlation

Brake switch / speed control Generic OBD-II High

What it means

P0504 means the two independent signals from the brake pedal switch (circuits A and B) disagree about whether the pedal is pressed. The car reads both to run brake lights, cruise control, the shift interlock, and, on some vehicles, push-button start. A misadjusted or failing switch, or a wiring/fuse fault, is the usual cause. The engine still runs, but the affected safety and convenience functions make this worth fixing quickly.

High

Can I keep driving? The car usually drives, but cruise control, brake lights, and on push-button cars even starting can be affected — get it fixed promptly.

Real-world scan data

Seen in

4,768

scans in the past year

Found in

0.8%

of scans

1.3%

of scans that found faults

Appears alongside · share of P0504 scans

P0401in 13.6% of scans

P0704in 12.2% of scans

P0402in 9.8% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

Common symptoms

What you'll notice

Cruise control won't engage or drops out
Brake lights behaving erratically or staying on/off
Check-engine light on
Shift interlock or push-button start may not release (won't shift out of park or won't crank)

Common causes

Most likely first

Misadjusted or faulty brake pedal switchLikely
Wiring or connector fault in the brake switch circuitCommon
Blown brake-light fuse affecting one of the two signalsCommon
Faulty control module reading the switch (less common)Less often

How to diagnose & fix

Work through it in order

Scan live data and compare the two brake switch signals as the pedal is pressed.
Check the brake pedal switch adjustment and the striker/plunger at the pedal.
Inspect the switch connector, wiring, and brake-light fuse.
Replace the brake pedal switch if the two signals don't agree correctly.
Verify both signals track together after the repair. Clear and re-test.

FAQ

Quick answers

Is it safe to drive with P0504?+

The engine runs, but disagreeing brake switch signals can disable cruise control and affect brake lights or the shift interlock, which is a safety concern. Repair it promptly.

Can I just clear P0504?+

It returns as soon as the two signals disagree again unless the switch or its wiring is fixed.

Read & clear P0504 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX