I’m not familiar withe the fusion but do you know what brands the new oxygen sensors are, oem or similar? I have seen some cars still throw a code that had an off brand sensor. You say 3 sensors where changed, how many total does the car have? While its not impossible, that seems like pretty low mileage for a cat to go bad. If i were you I’d have an independent shop diagnose the problem before you throw parts at it hoping to fix it.
that’s where a trained and experienced mechanic comes in
As far as I’m aware, there’s nobody that can do everything
That’s why you pay somebody else to do what you can’t, don’t have time for, etc.
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True, but I said there is no diagnostic. I didn’t mean for the DIY but generally.
no diagnostic, huh?
I’m not sure where you’re getting your information
ever hear of factory service manuals, trouble trees, not to mention knowing where to start your diagnosis, based on experience and common sense . . . ?
I’m not sure if I understand you correctly . . . but are you implying that every fault code means the mechanic has to guess, because there’s “no diagnostic” . . . ?
when I retrieve fault codes, I may not instantly know what the problem is, but I know how to start my diagnosis
The purpose of fault codes is not to tell the guy retrieving the code “Hey listen up, this is the part you need to replace. I guarantee it will resolve the problem.” That’s not how things work. The fault code is really just part of the early stages of your overall diagnosis
I’ve tried to explain this in some more detail, but perhaps we’ll just have to agree to disagree . . . ?
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Just a note here, I recently saw a television report that mentioned someone studying fuel quality and while there was little or no difference in the quality of REGULAR and PREMIUM there was considerable difference in the quality among the major branded fuels and the off brands. To play it safe I thought it would be worthwhile to pay a few cents more for Chevron or Texaco rather than the private brands.
Just to put everybody’s minds at ease, these are the Top Tier gasoline brands.
http://www.toptiergas.com/licensedbrands/
Tester
As regards codes and diagnostics, I think it’s important to recognize that onboard diagnostic systems were never intended to diagnose the root cause of failures. Their function is to monitor all of those systems that are mandated by the feds for emissions and safety and notify you if one of the OBD system sensors detects a signal outside of its normal range, suggesting an emissions or safety system malfunctioning. It’s truly a blessing that OBD systems tell us as much as they do, but it’s up to the diagnostician to determine why the sensor is sending a malfunction signal.
Often, with the right code reader, the OBDII system can help him do that. Often it needs an engine analyzer, or a compression gage, or a vacuum gage, or other equipment and tests that requires the training and experience that a good diagnostician possesses. Sometimes experience allows the diagnostician to immediately recognize the root cause of a fault code.
And there are many, many things that go wrong with cars that are with systems or parts other than those monitored for statutory compliance. There’s also diagnostic equipment for many of these problems, but sometimes none that’s relevant. Yeah, sometimes it takes simply replacing the most likely part and seeing if that works.
And then there are electrical problems… blegh!!! 
In summary, there’s a common misconception that fault codes are there to troubleshoot problems. That’s a misunderstanding of their function. Troubleshooting is the technician’s job. Fault codes are only there to tell the owner that the car is noncompliant with a federal emissions or safety mandate… and needs to go to a mechanic for troubleshooting.
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Of all those top tier gasolines listed, only 2 are in my area and I won’t use one because the station and owner are notorious for never checking for water in their tanks. I don’t want to use the other one because it is Russian owned. The oil company not necessarily the local station.
There are another 8 yjay used to be in our area but are not now.
I was speaking specifically about the code for general emissions problem. The shop manual lists a number of components that might be the problem and doesn’t have a diagnostic for each component. Or if there is a diagnostic it might involve removing the component and putting it through a diagnostic (like vacuum checking different ports checking for a blown diaphragm) but at $90/hour mechanics don’t do that. So you’re back to changing parts. At that point, you’re correct, experience helps by knowing which components for a specific model are most apt to fail.
In my experience I have never found a dealer or independent mechanic who will tell the customer that after replacing an emissions component and resetting the CEL that he guarantees that the light won’t come back on in the next few days and if it does the shop will pay for additional components. If you have, then I stand corrected, and I will take my work to that shop.
Expecting someone to stand behind the work done is one thing. Expecting someone to agree to fixing future problems that cause the light to come on is unreasonable.
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Clearly, the guys you’ve encountered don’t know . . . or don’t care . . . how to properly verify a repair. If you read the parameters for setting a fault code, you can also figure out how to verify that the problem is resolved. That includes, among other things, letting readiness monitors run to completion after repairing the problem and clearing the code(s) . . . I’ll take certainty over guesswork
Honestly, I don’t know how some shops survive, if they’re just gambling that a problem will be fixed, and the customer won’t come back with the same problem
As for finding a shop that understands and PRACTICES “verify the repair” . . . I have no advice
I think you misunderstood the comment. Let’s say the CEL was due to a coil pack. Repaired, CEL cleared, all is good. Two weeks later the MAF dies. How would verifying the repair of coil predict MAF failure?
I suspect that many just think that if the customer returns with the same problem, they’ll “find” an additional cause and charge the customer even more. Go back to start and repeat until the proper part is finally replaced. And many probably get away with it often. The world is, unfortunately, full of crooked, bad, and/or complacent people making a fortune screwing people. Fortunately, there are also good, competent, honest people too. The trick is finding the latter before the former. 
I’m talking about the next few days. That’s the same problem, not a future problem.
If you visit a physician for a sore throat, and he gives you a medicine that you discover didn’t work two days later, do you expect the physician to continue your sore throat treatment gratis? I don’t think so. The expectation you as a customer have is that the shop (or physician) perform the service in a manner consistent with a professional of their training and expertise, acting at all times with due diligence. Pro’s don’t guarantee immediate results, only that they are acting in what they believe is the customer’s best interest.