There is lots of videos and help around the net for this one, but maybe details of my experience will help someone because there are a couple twists. This job is something that an average person with a good sense of humor can do. It is an exercise in inconvenience but not mechanically complex. It doesn't take any more tools than a socket wrench and a jack stand. You do need a cheap tool to remove the sensor that you can buy when you buy the sensor.
Check engine light comes on. Within a day I get the notice for my bi-yearly emissions inspection. Life is like this sometimes. Need to fix it today. You can see i also need an oil change.
My 20 year old OBD reader (can get the auto parts store to do this for you also) says P0141 Faulty Heated Oxygen Sensor (H2OS) Bank 1 Sensor 2. Number 2 means the sensor on the catalytic converter under the car, not the one on the exhaust manifold under the hood. My car is a 2007 Honda Accord EX 2.4L 4 Cylinder.
This could be due to bad wires, but most likely the O2 sensor is just bad, this car is 10 years old now.
You can look under the car and see this thing on the side of the catalytic converter. I didn't do any diagnosis, i just replaced the sensor.
These are not too expensive, used to be a lot more. I bought this one for $26.
You also need a special socket wrench. I understand that auto parts stores may lend you one for a deposit, but they are only a couple bucks if you buy a cheap one, and this was the cheapest and worked just fine.
Parts came quickly. The sensor has a long wire that runs through some clips and eventually has a grommet in the floor of the car under the passenger's seat. Nuts! It is under a flap of carpet that you could possibly access by pushing the seat all the way up and reaching under but removing the seat is actually very easy and makes this job less of pain. The wire plugs in to a connector under the seat.
Do your self a favor and remove the seat as the first step. Just take out the four bolts, two in front and two in rear under some plastic covers that snap off and back on. Bolts come out easily with a socket wrench and the seat lifts up and you can reach the connector.
Unplug it and push the grommet and wire through the hole in the floor. Here it is hanging out the bottom of the car now.
I'm not a fan of being crushed under my car, so i jacked up the front right wheel and put a jack stand under it, next to the jack. I chocked the two rear wheels and pulled the emergency brake. That created just enough room to get under and do the deed. Still very awkward.
Reached under, put on the socket tool ,attached a socket wrench, wiggled and pushed and sensor was stuck tight. I took a small sledge hammer and hit the socket wrench a few times. Not an easy task while reaching under the car. Eventually it budged and I could use the socket and wrench to remove the sensor. Touch and go there for a while. I knocked a lot of rust off the cat in the process. My heat shields were already attached by some big hose clamps from home depot because they had come loose years ago.
The white plastic clips come off with a little pry from a screwdriver. I removed the old cable from the clips.
Installed the new sensor with the wrench. Routed the cable through the clips and pushed it and the grommet up through the hole in the floor.
From inside the car i connected the cable and pushed the grommet into place.
Reattached the seat without any issue, lowered the car. Here is where the fun part begins!
Started up the car just fine, and the check engine light is still on. Read the codes and it still says P0141. Played around a bit starting the car and reading it. Check engine light is still on and code persists. Looks like I need to reset the code. My old reader won't erase the code, it just says Err when i press and hold erase. Dang. Tried many times. Can't reset the code.
I decide to take it to the local auto supply store and get them to reset it. They tell me they aren't allowed to do a reset. Some posts say you can ask them to push the button yourself, but i didn't try that. I get frustrated and go buy myself lunch.
I need to get the car emission tested and I have to clear that light TODAY. While eating lunch and reading on the web I see I can disconnect the battery and press the horn to drain all the charge as an alternative to erasing the code with an OBD reader. However I'm out to lunch with no tools. But when i get back in the car WooT! The code has disappeared by itself. Problem solved. It just needed some driving and a few more starts to clear the fault code.
I drive immediately to the emissions inspection station and get it tested. It passed! Hooray. A big win.