I have a 2013 Honda Accord EX 4 CYL w/155K miles and am in the process of running down P0420 code. It has been suggested that it is a bad CAT. When I spoke to a CAT manufacturer they said that a CAT usually just doesn't go bad on its own and that something else is likely causing the problem. One of the metrics I am checking is the fuel trim numbers and according to my FIXD report the trim values are 3.13% for STFT and 2.34% for LTFT. I have read that values normally range from -10% to +10%, but I am not sure if this is correct. Are the numbers I am getting in a satisfactory range?

 

"Cats dont fail" is an old school of thought that ignores the changes in size,weight, and modern fueling and catalyst monitoring strategies.

On most modern vehicles if the efficiency falls below 99%, that cat is deemed a failure.

Despite the fact that the cat will easily pass a sniffer( emissions analyzer,) the PCM relies heavily on the EWMA formula and will deem the cat a failure if it falls out side of its parameters.

Long term trim is considered "good" if it falls between -10 to +10. These numbers rarely change and represent the overall fueling strategy. Perfect trim would be 0% and the closer you are to that number the better, but you wont see that on any current vehicle.

Short term trim is a representation of real time fueling strategy. As such, this number will oscillate during driving. -5% to +5 is ideal.

If the trim numbers are good, there are no exhaust leaks and there are no PCM reflash updates for this code, then you need a cat.

Cat monitors are very robust and very rarely(if ever) set a false code on a modern vehicle.( if the above conditions are good)

 

I have also tested ignition coils (COP) and am getting a 1.2 ohm reading on all 4 (cold). Any chance that the coils can go bad (throw a P0420 code) when heated during driving? I blew air up the tailpipe and found no leaks. In fact I removed the F/A sensor on the front cat during the process of blowing air in the tail pipe and experienced pretty good air flow coming out the port...so it appears that the cat is not clogged. My check engines light is intermittent. Is that consistent with a bad cat or maybe more like bad coils?

 

There is no easy way to tell you this. Your cat is dead. Sorry for your loss.

 

So does that mean it died on its own and likely that NOTHING caused it to die? Would a dead cat be clogged? Really don't want to invest in new cat if its going to die due to external causes.

 

How many miles are on it? They don't last forever. I have had a few modern Hondas only get 60k out of their original cats. Oddly they were all out of California. Guess California causes cancer in cars too?

 

HA!!

 

All things being equal, heat and vibration will cause it to die past 100k.

I wanna say modern vehicle cats probably last around 100k-150k. Of course there are always outliers but in my considerable experience, thats the average lifespan....

 

My accord has 155K miles on it. If I do need the cat, any recommendations for a cat and where to get it )preferable without breaking the bank)? Honda dealer wanted $2K!

 

OEM Honda. The aftermarket cats fall apart in about 20k miles.

Might save a little up front but they don't last. Either the honeycomb inside breaks apart and blocks the exhaust or they start tossing another P0420.

Nothing cheap about doing this correctly. The precious metals inside that nake it work are crazy valuable.

 

ugh...how about cats from rock auto?

 

If its CARB approved it will be as good as a dealer cat.

Otherwise its a crapshoot.....

 

Thanks to everyone for your responses!