Q: I had O2 sensor replaced twice in 4 months, but the engine light came on again 2011 Audi A6.

Hi there. If the check engine light is still on for the oxygen sensors, look at the description of the code to see if the sensor relates to a lean or rich condition. If the code does not, then there could be a broken wire on the harness to one or both sensors. If the code does have a lean or rich condition, then check the following:

Check

• The engine coolant temperature sensor is not working properly
• A leaking exhaust manifold or a leak in the exhaust system
• The spark timing is retarded
• There is a leaking fuel injector or there is high fuel pressure
• The engine has a cylinder misfire
• The engine oil is contaminated

These symptoms are more related to what can cause an oxygen sensor to record as the engine is running. If you need further assistance with your check engine light, then seek out a professional, such as one from Your Mechanic, to help you.