After replacing the catalytic convertor code P0420 came back?

Hi ehauser,

First point is, you are correct in the fact that there is only 1 catalytic convertor, 'if' you have the non-turbo. I am finding conflicting information if the Turbo has 2, but that is a potential (sometimes referred to as a resonator - but that is not a catalytic convertor)
Second point is, if the code came back and it's now off, the dealer likely did a code clearing process to it and if it hasn't come back right away, there is another issue and/or it's an intermittent problem.
Third point is, did the dealer do an actual diagnostic or just jump to saying it's the catalytic convertor? And, unless the catalytic convertor is 'plugged', it cannot cause damage to the engine -- it's the other way around where the engine damages the cat if it is not running properly.

There's a rather long diagnostic procedure that I will give you for reference:

P0420: Catalyst Efficiency Below Threshold

Related Vehicles: 2012-2018 Veloster 1.6L GDI

Notes/Hints:

Check the downstream O2 sensor. If the sensors signal is dropping when it shouldn't, or reading low voltage during WOT, replace it first, clear code(s) and recheck before condemning the catalytic converter.
If any other DTC's are displayed along with P0420, diagnose and repair those first before proceeding, especially any misfire or ignition related DTC's.
If any drivability issues exist along with the subject code(s), especially a lack of power, check fuel trims for adding fuel (High Positive). This is an indication the catalyst may be clogged or other exhaust restrictions exist.
Make sure no exhaust leaks exist, especially at or around the secondary O2 sensor. Smoke test to verify.
Apply a rich and then a lean condition while watching the downstream Oxygen Sensor in scan tool data. It should take a little longer to change showing the catalysts OSC (oxygen storage capacity) is sufficient. If the downstream O2 sensor switches the same or mirrors the upstream sensor, the catalyst is more than likely faulty.
If the catalytic converter needs replacement, technicians are reporting to use only OEM units.
When replacing the catalytic converter, it's good practice to replace the upstream O2 sensor at the same time.
Preliminary Tasks:

Review any available TSB's related to the subject code(s).
Review available vehicle history.
Perform all testing on a fully warmed up engine (in closed loop).
Check Heated Oxygen Sensor (HO2S) fuses and circuits.
Review wiring, vacuum diagrams and connector views for your specific application.
Follow all manufacturer safety precautions and warnings.
Diagnosis:

1. Warm the engine to operating temperature, clear the DTC, and test drive. Does the DTC reset?
--> If Yes, refer to step 2.
--> If No, condition is intermittent

2. Are there any air induction system vacuum leaks, or exhaust system leaks?
--> If Yes, remedy as necessary and retest.
--> If No, refer to step 3.

3. Is the rear oxygen sensor is switching (lean to rich) at a steady cruise speed?
--> If Yes, replace the catalytic converter, and retest.
--> If No, refer to step 4.

4. Refer to the Notes/Hints above and review factory troubleshooting. If all testing proves out good, suspect an intermittent issue or possible ECM/PCM problem.

And, in case you didn't know, there is a recall that you would want to check out as it was just released that I found. I would inquire about the potential of cat damage and would that fall under the recall repair.
https://cars.usnews.com/cars-trucks/hyundai/veloster/2015/reliability

Best of luck, Glenn

I not one that talks badly about other mechanics and repair shops (since I was one and owned one) but not all are scrupulous. Your copy of the completed repair order should have everything they did and the readings they got - if a diagnostic was done, it will have the info about it. If a diagnostic was not completed, then it could be deemed an unnecessary repair, especially if the 420 code returns (which it has already once and it's recorded). Did you get a copy of a work order for that visit?

What State do you live in? I want to see if there is a State Agency that overseas emissions and/or general automotive repairs, especially if they were improper. I'm not saying they were, but info for you in case there are continued issues.

Wait? You said they checked the "cam bearings" for the recall? The recall is not for cam bearings. It is about "connecting rod bearings" that are completely different. From the recall: "Hyundai Motor America (Hyundai) is recalling certain 2015-2016 Veloster, 2012 Santa Fe, 2011-2013 Sonata Hybrid, and 2016 Sonata Hybrid vehicles. The connecting rod bearings inside the engine may wear prematurely, which over time can result in engine damage." Further: "Dealers will also install a software update containing a new Knock Sensor Detection System (KSDS)." Was the update done?

Please get back to me. Glenn

Goodness. I took me a couple of hours on the internet and on the phone to find out where and how to file an automotive repair complaint. It's almost like they don't want anyone to know how to do it(?).

https://www.tn.gov/content/tn/attorneygeneral/working-for-tennessee/consumer/file-a-complaint.html

1) Go to link and click on "Online Complaint through CORE"
2) at the bottom right, click on "Continue as Guest", unless you want to register an account, then click the "Cancel" and that takes you to the appropriate page to register. As a Guest, you will not be able to track the progress of your complaint - it's close to an anonymous complaint. Register, and then for sure it's from "you" and you can follow it's progress.
3) Once you register and login, or click as Guest, the next page it takes you to determines what the complaint is about. For automotive, there is a potential for 2 choices. 'Consumer Affairs' would handle the complaint for 'improper repairs', and the 'Motor Vehicle' would handle the complaint for monetary relief. I would do the 'Consumer Affairs' first and let the complaint process do it's course and see if you might have a claim for monetary compensation, and then file that one.
4) Consumer Affairs choice gives you an option in the next box. Choose 'Consumer Affairs Complaints'. Under Motor Vehicles would be 'Motor Vehicle Dealers'. Beyond that, I have no idea. That's as far as I could get. I'm sure there is a paper filing process too because you would want to include copies of your work orders with the complaint.

Of course, this info may be all for naught if the 420 code no longer comes back. But, this is your potential recourse if it continues to come back.

I recommend you get a code scanner if you don't already have one (some are around $50.00). Photograph the scanner for any codes shown.

I truly hope the cat issue is over and done with, but if it isn't, the info above will help appropriately and correctly resolve it.

Be well, Glenn