Audi P0401 Code — EGR Flow Insufficient
The P0401 code on your Audi indicates insufficient flow in the Exhaust Gas Recirculation (EGR) system.
What It Means
The EGR system recirculates exhaust gases back into the engine to reduce temperature and emissions.
👉 If it fails:
- engine temperature increases
- performance drops
- errors appear
Common Causes
1. Clogged EGR Valve
5
Most common cause.
Reasons:
- carbon buildup
- soot
- poor fuel quality
2. Faulty EGR Valve
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Symptoms:
- rough engine
- hesitation
3. Blocked EGR Passages
- carbon deposits
- restricted flow
4. Sensor Problems
- pressure sensor
- temperature sensor
5. Vacuum or Control Issues
- leaks
- faulty control valves
Symptoms
- check engine light
- reduced power
- rough engine
- increased fuel consumption
Step-by-Step Fix
- Scan code
- Clean EGR valve
- Check passages
- Inspect sensors
- Replace EGR if needed
Can You Drive?
⚠️ Yes, but not recommended
👉 the issue will worsen
How much does the repair cost?
Cleaning: $20–100
EGR replacement: $150–400+