The Quick Answer above is the generic definition. What follows is the model-specific detail for the Audi models that log P0504.
DTC/P0504·Audi
P0504 on Audi: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeverityNot safe to driveAudi
P0504 on a Audi 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.
Typical repair cost, all makes€20 - €150
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Audi A4
2008-2024B8 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.
What causes P0504 on a Audi?
Beyond the generic causes listed on the main P0504 page, these are the patterns noted for Audi models:
Audi A4Brake switch plunger sticking on B8 A4
Audi A4Connector pin push-out after pedal box service
How to diagnose P0504 on a Audi with OBD2
Follow these steps to pinpoint the root cause of P0504:
- 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
- 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
- Remove the connector and inspect for bent pins or corrosion. Reseat firmly and recheck
- If both signals stay correlated only when the connector is wiggled, repair the wiring. Otherwise, replace the brake switch as a unit
- Clear codes, perform any required relearn for cruise control, and confirm the brake lights work both at rest and when the pedal is pressed
How much does P0504 cost to fix on a Audi? (EUR)
Estimated repair costs for P0504 in EUR, compiled across makes. Expect Audi parts and labour towards the upper end of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Codes related to P0504
These codes are often seen alongside P0504 or point to related issues, on any make:
P0571P0572P0573P0703U0140
Looking for the full P0504 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0504 guideSkanyx · Audi
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