2015 2.5L with bad catalytic converter - P0420

[Andy B]

I bought this car used about 6 months ago for my son to drive at college. It has ~120k miles.

 

A few days ago it pitched a P0420 code. I had him take it into a Midas that I've had good experience with in the past.

They did an analysis and determined that the car needed a new catalytic converter.

I had them replace the converter but I am worried because I've read that cats shouldn't go bad unless something else is wrong (bad spark plugs, etc.).

Should I be worried? Is there anything I should do at this point? Some basic things to check? Should I replace the spark plugs or anything else just in case?

[bbf2530]

1 hour ago, Andy B said:

I bought this car used about 6 months ago for my son to drive at college. It has ~120k miles.

 

A few days ago it pitched a P0420 code. I had him take it into a Midas that I've had good experience with in the past.

They did an analysis and determined that the car needed a new catalytic converter.

I had them replace the converter but I am worried because I've read that cats shouldn't go bad unless something else is wrong (bad spark plugs, etc.).

Should I be worried? Is there anything I should do at this point? Some basic things to check? Should I replace the spark plugs or anything else just in case?

 

Hi Andy and welcome to the Ford Fusion Forum. First...the cynical side of things: Were there any drive-ability issues, or just the Check Engine light? What "analysis" did they perform to decide it was the catalytic converter? Did you get a second (and even third) opinion from another shop?

Here is a good discussion of a P0420 DTC code: https://www.way.com/blog/p0420-code-what-it-is-and-how-to-fix-it/

 

As you can see, there are various causes which can set off a P0420 DTC code. So...did they properly diagnose the underlying cause of your P0420 DFC?

 

Now the optimist: You went someplace that you previously have had good experience with. You feel they do good work, so let's hope they do.

 

Next: Catalytic converters do fail sometimes. Even without bad plugs etc., and with even less mileage than yours. Not often, but it happens. 

Next: Yes, your scenario that there was another cause is also entirely possible. There could have been an engine issue which caused the catalytic converter fail. However, I would hope that this Midas shop would perform the proper diagnosis fo all possible causes, before replacing the catalytic converter.

Next: If the Check Engine light does not return, you can proceed with a reasonable assumption that things are okay.

 

Next: The vehicle has ~120,000 miles on it. Have the plugs even been changed? Required Maintenance for the plugs are to change 100,000 miles. Many would advise changing them sooner. Even every 50,000-70,000 miles. If you do not have reliable service records, I would advise changing the plugs. And also performing all other maintenance through ~120,000 miles on the schedule, which you can not verify was previously performed.

You can download the PDF versions of the Owners Manual and other guides/manuals here: https://www.fleet.ford.com/parts-service/resources/owner-manuals/

 

Finally...My advice would also be to ask these same questions at the Midas shop. Ask them to explain what they did to diagnose the actual cause. What is the warranty on the new catalytic converters...etc...etc. And keep asking questions until you are satisfied with the answers.

 

Let us know how you make out and good luck.

[Andy B]

There were no drivability issues. Just the light.

The shop originally suggested that it was probably one of the O2 sensors and that I could either pay the $150 diagnosis fee or just replace both O2 sensors to see if the light clears.

I decided to pay the $150. They measured both O2 sensors and the sensors were good. I am not sure if he did any additional analysis before deciding it was the cat.

I read through the post you linked above and I guess I probably should have tried just clearing the code to see if it came back but at this point, the cat is replaced.

I did lookup the maintenance schedule by VIN at ford.com and I have no records of previous maintenance so I will go ahead and replace the plugs (with autolite or motorcraft per the various posts I've read here).

 

Thanks for your time.

[bbf2530]

6 hours ago, Andy B said:

There were no drivability issues. Just the light.

The shop originally suggested that it was probably one of the O2 sensors and that I could either pay the $150 diagnosis fee or just replace both O2 sensors to see if the light clears.

I decided to pay the $150. They measured both O2 sensors and the sensors were good. I am not sure if he did any additional analysis before deciding it was the cat.

I read through the post you linked above and I guess I probably should have tried just clearing the code to see if it came back but at this point, the cat is replaced.

I did lookup the maintenance schedule by VIN at ford.com and I have no records of previous maintenance so I will go ahead and replace the plugs (with autolite or motorcraft per the various posts I've read here).

 

Thanks for your time.

 

Hi Andy. Hope it is all straightened out for you.

 

On a related note: I would recommend using the Motorcraft plugs. And if you do not have maintenance records, it would be a good idea to flush/fill the transmission and cooling systems, and the PTU (if it is AWD).

 

Let us know how you make out and good luck.

[WKelley]

My .02$ : check the gaps on new plugs.  I chased a bogus misfire that was due to wrongly gapped new plugs.

[bbf2530]

Hi Andy. What WKelley stated above. Whatever brand plugs you purchase, double check the gap before installing them. While they should have the correct gap out of the box, there is no guarantee that they do.

 

Let us know how you make out and good luck.