Where is O2 sensor on 97 Oldsmobile Achieva 2.4 liter engine?

The O2 sensor location on a 1997 Oldsmobile Achieva with a 2.4L engine is typically in the exhaust manifold, before the catalytic converter. There's usually one upstream (before the cat) and one downstream (after the cat). The upstream sensor is the more important one for engine control.

However, without a specific diagram for your vehicle, I can't pinpoint the exact location. It's best to:

* Consult a repair manual: A Haynes or Chilton manual for your specific year and model will have diagrams showing the exact location.

* Use an online parts diagram: Many auto parts websites (like AutoZone, Advance Auto Parts, etc.) allow you to look up parts diagrams for your vehicle. Search for your car and look for the oxygen sensor diagram.

* Check under the car: Look closely at the exhaust manifold near where the exhaust pipe exits. The sensor will be threaded into the manifold. It's usually a cylindrical device with a wire harness connected. Be careful when looking under the car, the exhaust system is hot when the engine has recently been running.

Remember to always disconnect the negative battery terminal before working on the O2 sensor to prevent damaging any electrical components.