2006 Sonata Air/fuel ratio sensor
 

Hey!

I've got a 2006 Sonata XL 3.3. I'm trying to clear a code and turn off the CEL. The code being thrown is for an O2 sensor (Bank 2 Sensor 2). I replaced the sensor and cleared the code but the code came back after 5 minutes of driving.

Talking to a mechanic, they said since it's an import, they'll bet it's the Air/Fuel Ratio Sensor. I've never heard of that. So I go to price/research it and save money by replacing it myself so that I can take it for emissions testing this month. However, what I'm finding for the most part, is that the two are interchangeable, or the same thing.

Anyone know anything about this? Mostly I'm just trying to see if I need a mechanic to find a short in the circuit or replace a sensor somewhere, cause I don't have the time or money at this point to spend in a garage!

You didn't say what code precisely (number !). O2 sensor errors are often taken as problem of the sensor itself - which they are only in rare cases. Good revenue generator for the shops (customer can hardly argue against sensor replacement if shown the scantool printout stating some 'o2 sensor error'). Most times the sensor is just reacting to a problem nearby (which is its reason for existence ...). Downstream sensor may just 'see' a broken/inefficient cat, so even replacing the o2 sensor 10 times will not fix the problem.

I don't get the mechanic's statement 'since it's an import'. US vehicles use the same kind of emissions control equipment as imports do. And I'd like to know what an air/fuel ratio sensor should be. Basically this is nothing else than the o2 sensor (upstream / pre cat).
Go to some other shop. O2 sensors can easily be diagnosed using the data the engine ECU provides so there's no reason for replacing parts without using that evidence upfront (working that way most times is burning money and time)

I'm not looking at it at the moment but I believe it was a P158 and a P160.

I know how these mechanics work. He didn't even ask me how I knew it was an O2 code or if I knew what the number was. He just threw that out there.

The 158 is high voltage, the 160 is no activity. I think after replacing the old sensor, only the 158 remained, which leads me to believe that the old sensor burned out and hence became inactive.

I just wanted to be sure of what that mechanic said, seeing as I had no idea what he was talking about.

So I'm thinking maybe a short? How do I stinking track that down?! I'm horrible with electrical stuff.

Or possibly a bad left cat?

These 2 codes can mean a bunch of things but half of them would affect both banks and would likely also trigger upstream o2s codes: intake air leak, fuel pressure deviations, broken injectors.

Have you noticed anything like rough idle or elevated fuel consumption ?

It's helpful to compare fuel trim numbers btw bank1 and 2, the numbers should be close. Upstream sensors are used to trim fuel/air, downstream sensors monitor cat efficiency. So if something is wrong with fuel trim, upper o2ss will show and ECM will correct - resulting in trim numbers.
You seem to have that one b2s2 errors only, so what's left for that is the sensor itself (or its heater), the wiring or - worst case - the cat.

I've replaced the sensor, so it comes down to either the wiring or the cat.

As far as symptoms go, there has been an increased fuel consumption. Not horrible, but just noticeable. Maybe a drop from the 25-28 range to the 23-25 range. Idle is ok, smooth, however I have noticed an occasional, ever so slight hesitation upon take off from a stop, then it will thrust forward slightly harder than you would expect for the amount of throttle.

Because it's probably the more expensive option, I'm thinking I've got a bad cat that's causing things to go wonky. I mean, the car is 10 years old...and if I understand correctly, a bad cat could cause a rich reaction resulting in high sensor voltage, right?

I am quite interested in the diagnosis, the cat is a possibility.

Well, I took it to that same garage because I was at a loss and didn't want to spend money on something that wouldn't fix it. They had that car for two solid hours and couldn't find anything. They said they were struggling with unplugging the O2 to check the pins. They struggled with it for an hour. I took the car home and tried to mess with it myself. In less than two minutes, I noticed that two of the four wires were split!

I don't know how they missed it! But I guess such is life. I'm glad it was right there in the open. The CEL went out, and I've got 20 miles on the car now and it's still out!

What a trip. Sorry it was so anticlimactic!

Thanks for all your help, e3tom!

Congrats. Lucky you it was the cheapest of all imaginable causes. New MCC would have cost big $$$.

I am happy to hear that it was a simple fix, can't believe the shop missed it though. They must have been looking for something bigger.