Locate the front oxygen sensor in the exhaust manifold and the rear sensor at the end of the catalytic converter or the pipe just after it. Use a special oxygen-sensor socket, which many parts stores loan, rather than a 3/8 wrench.
The owner of a Saturn with a 1.9 DOHC engine asked where its two oxygen sensors are located after a mechanic suggested replacing them with a 3/8 wrench. The expert said the front sensor is in the exhaust manifold and accessible from the front, while the rear sensor is at the end of the catalytic converter or in the pipe just after it. A special socket was recommended, and the owner was asked why replacement was needed.
