* Before the catalytic converter: This is the most common location for the first O2 sensor (upstream sensor). Look for it in the exhaust manifold or very close to it. It'll be threaded into the exhaust pipe.
* After the catalytic converter: If your van has two O2 sensors, the second one (downstream sensor) will be located after the catalytic converter.
To find it definitively:
1. Consult your vehicle's repair manual: This is the best resource. It will have diagrams showing the exact sensor location(s) for your specific engine.
2. Use a parts diagram online: Many auto parts websites (like AutoZone, Advance Auto Parts, etc.) have online parts diagrams. Enter your van's year, make, model, and engine, and search for "oxygen sensor." The diagram will usually show the sensor's location.
3. Look for a wire harness leading to the exhaust: The O2 sensor has a wire harness connected to it. Follow the harness from under the hood; it will likely lead you to the sensor.
Warning: The exhaust system will be hot after the engine has run. Allow it to cool completely before attempting to locate or replace the sensor.
