Where is the front 02 sensor of 2004 Pontiac Aztec?

The front O2 sensor of a 2004 Pontiac Aztek is located on the exhaust manifold, just before the catalytic converter. It is typically positioned on the driver's side of the engine, where the exhaust gases exit the engine. You may need to lift the vehicle for better access, as it can be somewhat difficult to reach without proper clearance.