Replacing O2 Sensors

[SeldomSeenB]

My check engine light recently lit up and I got the computer code for the cause and it turns out that the 02 sensor needs to be replaced. I have read a little and here and there and from my understanding there are two sensors. So my questions are:

1. How do I know which sensor needs to be replaced since the code is not specific to which one?

2. Where are these sensors located and is replacing them something that I can do without needing to take my car to the shop.

Thanks in advance.

 

[MustangLX-5.0]

First,replacing your O2 sensors is a piece of cake.Get yourself an O2 sensor socket at your local auto parts store.The O2 sensors have wires coming out and the special socket has a slit made for that.

What was the specific code you got? Can you post it here?

There are a grand total of 4 O2 sensors.The 2 sensors in the front are just below the exhaust headers and above the first set of cats.These are your primaries.There is a second set just before the Y-pipe narrows into one piece.I wouldn't worry about these,unless they are the faulty ones.They only give info to the pcm as regards to how well the cats are doing their job.

Other than that,jack you car up and set the front end on jackstands.(NEVER work under just a jack).You can start by disconnecting the O2's from the harness.As for the sensors,it may take a little muscle to loosen them.Those fronts get super hot.Spray a little PB blaster and let it soak for 10 minutes.Then try removing them.The passenger side sensor is the most difficult one as you'll have very little clearance.I had to use a small pair of vice grips as I had rounded off mine ...take your time...

Once the sensors are out,clean out the leftover pb with brake cleaner (or carb cleaner).Apply anti-seize compound to the threads of the new sensors and screw them in.Tighten just a little with your wrench.Plug back in and your done.

 

[Skymarshal]

I just did mine. I had a CEL for low catalyst efficiency, which is one sign of O2 sensors going bad. As the sensors get older, they can't adjust quickly enough to changing engine RPM and allow a rich mixture. This can cause a variety of symptoms, including poor mileage and CEL codes concerning right or left bank mixture and catalyst efficiency.

You really don't need a O2 sensor socket unless your sensors are really tight. Mine loosened right up after a shot of penetrant and I was able to do the job with a big 22MM wrench. The whole job can be done under the car with the exception of the plug for the right front sensor, which is easier to get to from overhead.

 

[MustangLX-5.0]

SkyMarshal,were those CEL codes anywhere in the 420-439 range? -Catalyst Efficiency Below Threshhold Bank 1/2-.That's usually an indication that the converters aren't working properly anymore.I got those codes after I blew out my front cats from backfires (bad coil pack).I KNOW they are blown out because mounds of that charcoal honeycomb material blew all over the place.And the exhaust smells a lot more now.

That's the answer I got from 5 other techs here at work.

 

[Skymarshal]

The code was somewhere in that range, but I don't think my cats are bad. Unburned fuel in the exhaust can fool the computer into thinking that the cat isn't doing its job, triggering the code.

100 mi on the new sensors and so far the CEL hasn't come back on. When I reset the light before replacing the sensors, it came right back on, so the new sensors seem to have helped. We'll see...