Where is the O2 Sensor located on a 1998 Honda Civic Sedan?

Answer 1

There are two sensors, one before, and one after the catalytic converter. There are wires coming out, so they are hard to miss. The catalytic converter is connected to the exhaust manifold, which is connected directly to the engine. You can see it looking down at the open hood, towards the front of the car, attached to the engine. The top sensor sticks stright out of the exhaust manifold, the second sensor is down a little lower and to the left if you are facing the car from the front. Note: The exhaust manifold has a metal heat shield over it. You can remove the two bolts (12mm) holding the heat shield to inspect the exhaust manifold. It is VERY COMMON for some models to develop hairline cracks in the exhaust manifold right around the oxygen sensor (you might have to brush away rust to see the cracks). This could result in the check engine light going on indicating bad cat (even though there may not be anything wrong with your cat OR your sensors!). If you see cracks, either repair them or replace the manifold (unfortunately you typically cannot buy just the manifold, you have to buy a new cat with manifold - but you can sometimes find used manifolds or aftermarket cat+manifold for cheap). Some have used heat resistant expoxy to repair the cracks (welding is better though). If you use epoxy, look for a brand specifically made for exhaust systems. "JB Weld" epoxy from your hardware store may work for a couple weeks but is not a good solution.