Hello Azine,
been long time member of Azine. I have 05 TL original owner and back in November of last year, I got 2013 RDX Tech AWD.
Little history of the RDX. Got the car with only 49K original miles. I checked with Acura dealer since the has always been serviced at the dealership. In about 2K miles, I started getting the P0420 code. I know this is Bank 1 catalytic converter. So far, I’ve changed the downstream and upstream o2 sensors. After the o2 sensors, the car goes about 200miles with no check engine light. Then, the P0420 comes up again. I’ve tried the Gumout, Seafoam, Cataclean in the gas tank and again, good for about 200miles and then againP0420. Replacing the car will be my final move, but I was wondering if there is something else I can try. I was thinking about the defouler, but I kind of want to fix it the right away. Currently the car has 52K miles.

 

that's VERY strange that the cat is dying at that little mileage... what brand o2 sensors did you get.? THe downstream one is more important than the upstream with regards to that code. I'd consider replacing the cat before replacing the car, that exterme seems a bit heavy-handed.

 

I got the NTK o2 sensors from Rockauto. My last resort will be replacing the cat, but wonder why it runs about 200miles without any issues and then the P0420 comes back again. I just saw on 3G TL forum people using BG 44K fuel system cleaner. Wonder if I should give a try, but how long can I try additives before mess up something else 😨

 

The reason the code comes back is you didn't fix the problem. The likely culprit is a failing catalytic converter. I had to replace the cat in my 2006 Camry. I kept getting P0420; erasing the code and it would come back in 300 miles; then 200 miles and eventually within 10 miles of erasing the code. I knew the issue was the cat (mechanic diagnosed it) but it gave me time to save money for the repair.

Yes, it's low mileage but remember it's a 10-year old vehicle that you bought used. And you live in an area where the winters can be harsh (salt). If you have a mechanic you trust, I would have him/her do a formal diagnosis and give you a cost to repair. Also use an OEM cat. My mechanic let me bring in the parts. Saved me about $100 on the repair.

 

I agree with everything you said. I haven’t had a mechanic test and see if it is really the cat gone bad, but after everything I’ve done so far, it might be the cat. And yes, it is 10 year old car and who know what gas the previous owner has been using, I assume short trips too because of the low millage and those short trips didn’t really get the cat hot enough to do its job. I wonder if I use defouler, it will take car of the check engine light, but how will this affect the car/engine down the road because I plan on keeping this car just like my 05 TL.

 

The defouler is illegal in most areas (large cities, states, etc) that test for emissions. Basically you are tricking the O2 sensors which is modifying the exhaust. Your cat is still deteriorating and can cause engine issues when it fails, which you won't know until you start having issues.

If you want to keep this vehicle for a long time, get it fixed properly. And keep up with the maintenance.