P0504 on Audi: Causes, Symptoms and Fix Cost
Quick Answer
Not safe to drive
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. VW, Audi, Skoda and SEAT apps often show this code as P050400; the last two digits are a failure-type byte.
- Severity
- Moderate · Electrical
- Typical repair cost, all makes
- €20-€150
Connect a standard OBD2 adapter (Bluetooth LE on iPhone) to your Audi and Skanyx tells you what P0504 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.
Get Skanyx freeWhat does P0504 mean on a Audi?
The Quick Answer above is the generic definition. What follows is the model-specific detail for the Audi models that log P0504.
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.
What causes P0504 on a Audi?
Beyond the generic causes listed on the main P0504 page, these are the patterns noted for Audi models:
Brake switch plunger sticking on B8 A4
: Audi A4
Connector pin push-out after pedal box service
: Audi A4
How to diagnose P0504 on a Audi with OBD2
- 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.
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Adjust brake pedal position | €0–€0 | €20–€60 | €20–€60 | Easy |
| Replace brake light switch | €15–€40 | €20–€60 | €35–€100 | Easy |
| Repair brake switch wiring and connector | €5–€30 | €40–€120 | €45–€150 | Moderate |
Prices estimated as of October 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:
- P0571
- P0572
- P0573
- P0703
- U0140
Looking for the full P0504 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0504 guide