Guessing it's the catalytic converter or an O2 sensor. Vehicle has 140K miles on it. I don't really have the time or patience to diagnose the issue and I haven't been able to find a diagnostic scanner that will give me live O2 data. Any suggestions to quickly and easily diagnose the exact cause? Otherwise, I will likely just replace the cat and both sensors. I am considering a Magnaflow cat but Magnaflow told me my vehicle has two (2) cats. Can anyone confirm? Any cat recommendations?

Thanks for the help. Very much appreciated.

 

Replace the cat, or just get a defouler if you live in a state that doesn't inspect for emissions.

 

With the age / mileage of your TSX...a "defouler" or spacer is the way I'd go -or- there's also the "bypass method" where you wire-in a resister & capacitor into the O2 sensor harness. This assumes you can do this yourself (most mechanics won't) and that you don't have emissions inspections in your state.

 

I will look into the defouler/spacer option. But also, can either of you advise if I have one or two cats and which of the two cats linked to is appropriate for my vehicle? Very much appreciated.

 

Your 2.4L (4 cylinder) has one catalytic converter. The P0420 code is a result from the downstream O2 sensor. There are a few possible reasons for this code:
catalytic converter efficiency has dropped below 95%...it's one of those things where the car sees >95% efficiency and the cat is "gold," <94% efficiency and the cat is "sh*t"
bad O2 sensor
exhaust leak

note that downstream O2 sensor pretty much does nothing more than measure the health of the cat...it's info is not used to determine fuel/air mixture, etc., like the upstream O2 sensor.

 

Thank you. Very helpful! I'm going to check for leaks and if I can't find any I will just replace the O2 sensors and the cat. I really haven't had any other issues with this car so I plan to drive it for many more years.

 

Two cats. O2 sensor is on the primary cat.

Btw saw your PM but replying here so others can benefit - you'd only need to replace the primary cat to clear the code. Secondary cat doesn't have any sensor on it.

Given the primary cat is in the back of the engine bay and a huge PITA to access, you might be better off paying an exhaust shop to deal with it. They probably have Magnaflow cats in stock.

 

Ah. So it sounds like the primary cat is the manifold version? I'll get under there this weekend and see if it's something I can manage at the cost of a few raw knuckles. I'm not wed to Magnaflow -- that's just one option. The other option is the Walker OEM version from Rock Auto.

 

Quick correction to a prior post, looks like both cats in your TSX have a sensor, but the code is for the upstream (harder to reach of course) sensor.

For some reason the RDX doesn't have a downstream O2 sensor, but regular K24 exhausts do.

Either brand of cat should be fine - magnaflow is convenient because you can usually source them locally.

 

Hello,

Over the Thanksgiving break I got the code on my 2011 2.4 TSX that has 168K miles. The 2.4 4 cylinder has 1 CAT but with the P0420 thats pretty much a bad CAT?

 

Your TSX actually has 2 cats...but only one of them (cat right off the back of the engine) is related to the P0420 code

My advice...reset the code and see if it starts to come back consistently. If it does, you can then decide if you want to replace the cat -or- do one of the work-arounds mentioned above.

The code can "pop" for a few reasons:
-catalytic converter efficiency has dropped below 95%...it's one of those things where the computer sees >95% efficiency and the cat is "gold," <94% efficiency and the cat is "sh*t" and you get that P0420 code
-bad O2 sensor (downstream)
-exhaust leak

 

Unfortunately I did reset and I even purchased Rislone complete CAT cleaner and after about 168 miles the code came back. I'm in California so I need to replace the CAT with C.A.R.B approved.

Thank you,

 

I'd see how much an exhaust shop wants to fix it. That's likely your cheapest option outside of DIY'ing it.

 

the 2nd Cat doesn’t have any sensors so if that goes bad there isn’t any indication is bad?

im going to use some Cat cleaners before replacing it.