Q: How many O2 Sensors does 2009 Cadillac STS have?

Your car has 4 oxygen sensors in total. Two of the oxygen sensors are used to monitor the air fuel ratio in the six cylinders (one sensor for each bank of 3 cylinders). The other two oxygen sensors monitor the efficiency of the catalytic converters. Your car has two catalytic converters and so there are separate oxygen sensors for each converter. The sensors are long lived and should be tested using an appropriate scan tool before condemning them. If you desire a diagnostic on the sensors, and replacement if needed, please request oxygen sensor diagnostic/replacement and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.