Check Engine Light Due to Vacuum Leaks, Oxygen Sensor, or Catalytic Converter Fault on Audi S4

Vacuum leaks, oxygen sensor failure, and catalytic converter efficiency faults can cause the Check Engine Light to illuminate.

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Average mileage: 149,000 (149,000–149,000)
3 model years affected: 2000, 2001, 2002
5 people reported this problem
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problem details
2001 Audi S4 149,000 mi,
My check engine light hardly ever goes off. The problem from day one has been the oxygen sensors. I have had them replaced twice within the last three years and the problem has not gone away.