Check Engine Light Due to Vacuum Leaks, Oxygen Sensor, or Catalytic Converter Fault on Audi A4

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

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Average mileage: 99,757 (54,000–155,000)
Exhaust & Emissions affected: 1.8L 4 Cylinder Turbo
12 model years affected: 1997, 1998, 1999, 2000, more2001, 2002, 2003, 2004, 2005, 2006, 2010, 2012
28 people reported this problem
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problem details
2002 Audi A4 155,000 mi,
Catalytic converter is bad. :( must replace before next smog check.
check engine light on
2004 Audi A4 98,000 mi,
Blinking engine light - diagnosis bad hoses, etc in need of immediate repair.
2010 Audi A4 82,000 mi,
engine light came on, checked code and it read PO420 catalyctic converter maybe bad
Crankcase breaker system was replaced to correct check engine light fault. Symptoms were: check engine light and rough idle.