Vacuum leaks, oxygen sensor failure, and catalytic converter efficiency faults can cause the Check Engine Light to illuminate.Google+
Car Problem Reports
Audi A6 Quattro Check Engine Light Due to Vacuum Leaks, Oxygen Sensor, or Catalytic Converter Fault
Audi A6 Quattro Problem
Exhaust & Emissions Affected: 2.7L V6 Turbo
Average Mileage: 105,375 mi (80,000 mi - 135,000 mi)
Visitor, 2001 Audi A6 Quattro
the engine light is on and i cant drive the car cause it will cut off and oil is leaking
Visitor, 2001 Audi A6 Quattro, 80,000 mi
Have been told that it is the O2 sensor. I have had them replaced and the CEL is back after 10k miles.
Have this problem as well, need to assemble funds to fix it.
Visitor, 2002 Audi A6 Quattro, 120,000 mi
catalytic converter insufficient flow cause CEL on
check ingine light car seems to slow down and pick up at times
Visitor, 2002 Audi A6 Quattro, 128,000 mi
CEL on. Checked OBDCOM--diagnoses was improper Catalytic converter air mixture coming from back O2 Sensors. Will replace catalytic converters and O2 sensors.