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DTC/P0504

P0504: Brake Switch "A"/"B" Correlation

Quick Answer
Moderata GravitàNon sicuro da guidareImpianto elettrico

P0504 means the two internal circuits of the brake light switch do not agree. Modern brake switches send two signals to the ECU for safety: one that closes when the pedal is pressed and one that opens. If the ECU sees both circuits in the same state at the same time, it sets P0504. The fix is almost always a new brake switch, sometimes combined with a pedal position adjustment.

Costo di riparazione stimatoDa €20 a €150+, varia in base al veicolo

Cosa significa P0504?

P0504 means the two internal circuits of the brake light switch do not agree. Modern brake switches send two signals to the ECU for safety: one that closes when the pedal is pressed and one that opens. If the ECU sees both circuits in the same state at the same time, it sets P0504. The fix is almost always a new brake switch, sometimes combined with a pedal position adjustment.

P0504 è un codice diagnostico di guasto relativo a impianto elettrico, classificato con gravità moderate. Quando la centralina (ECU) del tuo veicolo rileva questa condizione, memorizza P0504 e accende la spia motore.

Quali sono i sintomi di P0504?

Se il tuo veicolo ha attivato P0504, potresti notare uno o più di questi sintomi:

  • Cruise control will not engage or drops out as soon as it is set
  • Brake lights stay on continuously or do not come on at all
  • Push-button start refuses to crank the engine
  • Automatic transmission will not shift out of Park
  • Stability control or hill-hold features disabled

Cosa causa P0504?

Ecco le cause più comuni di P0504, ordinate in base alla probabilità che siano la causa del problema:

altaFailed brake light switch (internal contacts disagree)
mediaBrake pedal misadjusted, holding the switch slightly pressed
bassaDamaged wiring or connector at the switch
bassaECU or BCM software fault (very rare)

È sicuro guidare con P0504?

No, risolvi subito il problema. Most modern brake pedal switches have two redundant circuits. When they disagree, the ECU cannot trust the brake pedal input. Cruise control will not work, brake lights may stay on or fail, and on push-button start vehicles the engine may refuse to start. Repair before extended driving.

Come si diagnostica P0504?

Segui questi passaggi per individuare la causa principale di P0504:

  1. Use a scan tool to view live brake switch data. Most ECUs show two signals (BLS and BTS or similar). Press the pedal and verify both change state cleanly together
  2. Inspect the pedal at rest. The switch plunger should be fully extended and resting against the pedal stop with no preload. A loose stop pad lets the pedal sit too low and pre-presses the switch
  3. Remove the connector and inspect for bent pins or corrosion. Reseat firmly and recheck
  4. If both signals stay correlated only when the connector is wiggled, repair the wiring. Otherwise, replace the brake switch as a unit
  5. Clear codes, perform any required relearn for cruise control, and confirm the brake lights work both at rest and when the pedal is pressed

Quanto costa riparare P0504?

I costi di riparazione di P0504 variano a seconda della causa principale e del tuo veicolo. Ecco le stime tipiche:

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Adjust brake pedal position €0–€0 €20–€60 €20–€60 Facile
Replace brake light switch €15–€40 €20–€60 €35–€100 Facile
Repair brake switch wiring and connector €5–€30 €40–€120 €45–€150 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

P0504 su veicoli specifici

P0504 si comporta in modo diverso a seconda del tuo veicolo. Seleziona la tua auto qui sotto per cause specifiche del modello, problemi noti e stime dei costi adeguate:

BMW

P0504 su BMW 3 Series

2005-2024

F30 3 Series with push-button start commonly fail to crank when the brake light switch loses correlation. BMW dealers see P0504 frequently around 80,000-120,000 km. The switch is inexpensive but the symptom (no-start) often sends owners to a tow truck before the diagnosis is made.

Cosa causa P0504 su una BMW 3 Series?

BMW 3 SeriesBrake switch internal contact failure on F30 push-button start
BMW 3 SeriesPedal stop pad disintegration letting pedal rest too low

Costo di riparazione di P0504 per BMW 3 Series

Costi stimati per i proprietari di BMW 3 Seriesadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici BMW

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Adjust brake pedal position €0–€0 €28–€84 €28–€84 Facile
Replace brake light switch €21–€56 €28–€84 €49–€140 Facile
Repair brake switch wiring and connector €7–€42 €56–€168 €63–€210 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Volkswagen

P0504 su Volkswagen Golf

2003-2024

Mk6 and Mk7 Golf are covered by a 2014 VW recall for brake light switch failures that produce P0504 and erratic brake lights. The recall replacement is free of charge at VW dealers if not already done. Check the recall status by VIN before buying a switch from an aftermarket supplier.

Cosa causa P0504 su una Volkswagen Golf?

Volkswagen GolfRecalled brake light switch on Mk6/Mk7 (2014 VW recall)
Volkswagen GolfPedal sensor misalignment after clutch master cylinder replacement

Costo di riparazione di P0504 per Volkswagen Golf

Costi stimati per i proprietari di Volkswagen Golfadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Volkswagen

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Adjust brake pedal position €0–€0 €23–€69 €23–€69 Facile
Replace brake light switch €17–€46 €23–€69 €40–€115 Facile
Repair brake switch wiring and connector €6–€35 €46–€138 €52–€173 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Mercedes-Benz

P0504 su Mercedes C-Class

2008-2024

W204 and W205 C-Class have well-documented brake switch failures, often setting P0504 together with a fault for stop-start system disabled. Mercedes uses a more complex switch with multiple internal contacts, so a single broken contact triggers the code. Cruise control and stop-start return to normal after replacement.

Cosa causa P0504 su una Mercedes C-Class?

Mercedes C-ClassMulti-contact brake switch internal failure on W204/W205
Mercedes C-ClassStop-start system disabled as secondary symptom

Costo di riparazione di P0504 per Mercedes C-Class

Costi stimati per i proprietari di Mercedes C-Classadeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Mercedes-Benz

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Adjust brake pedal position €0–€0 €27–€81 €27–€81 Facile
Replace brake light switch €20–€54 €27–€81 €47–€135 Facile
Repair brake switch wiring and connector €7–€41 €54–€162 €61–€203 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Audi

P0504 su Audi A4

2008-2024

B8 A4 owners frequently report P0504 from a sticking brake switch plunger. The plastic plunger swells slightly with age and stops returning fully when the pedal is released, so the two internal contacts disagree. Replacement takes 15 minutes and uses the same switch as several VAG models.

Cosa causa P0504 su una Audi A4?

Audi A4Brake switch plunger sticking on B8 A4
Audi A4Connector pin push-out after pedal box service

Costo di riparazione di P0504 per Audi A4

Costi stimati per i proprietari di Audi A4adeguato al rialzo rispetto alla media a causa dei prezzi dei ricambi specifici Audi

Riparazione Costo dei ricambi Costo della manodopera Stima totale Difficoltà fai-da-te
Adjust brake pedal position €0–€0 €25–€75 €25–€75 Facile
Replace brake light switch €19–€50 €25–€75 €44–€125 Facile
Repair brake switch wiring and connector €6–€38 €50–€150 €56–€188 Moderata

Prezzi stimati al March 2026. I costi variano in base alla regione, al veicolo e all'officina.

Questi codici compaiono spesso insieme a P0504 o indicano problemi correlati:

P0571P0572P0573P0703U0140

Domande frequenti su P0504

Why won't my car start after the brake light switch failed?

Push-button start vehicles require the brake pedal to be pressed before the engine will crank. The ECU checks the brake switch signal to confirm the pedal is depressed. If P0504 is set, the ECU cannot trust that signal and refuses to start as a safety measure.

Can I just replace the brake light switch myself?

On most cars yes. The switch is a small plastic part that twists or clips into a bracket above the brake pedal. The job typically takes 10 to 15 minutes and requires no special tools. Just disconnect the battery before unplugging the switch to avoid airbag warnings.

Why are my brake lights stuck on all the time?

A stuck-on circuit inside a failing brake switch is one of the classic P0504 symptoms. The pedal-released contact has welded closed, so the brake lights stay on even with the pedal up. Replace the switch to fix.

Will a recalled brake switch cause P0504?

Yes. VW issued a 2014 recall covering brake light switches on certain Golf, Polo, and Audi models because the internal contacts could disagree, triggering P0504 and causing erratic brake light behaviour. Check the recall status with your VIN before paying for parts.

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