Catalytic converter cleaning is a thing?

So a friend asks who to take their car to to have the converter cleaned.

I've never heard of anyone doing this. She said the independent Subaru shop does it but won't on her Toyota. Says fault code P0420. I said that's catalyst efficiency below threshold. Probably something up stream causing a rich condition.

Thoughts?

all that means to me is hammering a tube through the cat to open it up.

Maybe she can get her injectors and transmission flushed at the same time.

It depends on what's causing the problem.

If it's sulfur, yes, you can clean that off with some WOT, and extended closed throttle-  get it hot, and some fresh air.

If it's anything else, no, it's not possible.  The most common catalyst poison is phosphorus, which takes an acid bath to get off.  Actually, that's pretty much the only poison agent these days- and it comes from the oil.

If it's just cause by an old catalyst- there's nothing you can do with it.

FWIW, if it's running rich, the system would tell you that, too.  If you had a recorder, you could see it.  

The "cheap" fix is to change the front O2 sensor (the rear one rarely goes bad, as there's a catalyst in front of it).

FWIW, I had two 420s this month where the rear O2 was unable to read over .3-.4v even if the engine was forced rich, and the PCM was too stupid to recognize that as a failed rear oxygen sensor.

Both were Nissans, which kind of reinforces the stereotype that Nissan internal diagnostics are nearly useless.

Guess who also uses the same/similar electronics as Nissan.  Starts with an S, is relevant to the discussion...

Either because the engines are inherently dirty or the parameters are too finely defined, Subarus are horrible for catalyst inefficiency..  Replace the cat with an aftermarket one and it WILL fail again.  You must, must, must use an actual Subaru converter.  Yes it's expensive.  But first you must verify that the sensors are actually reading correctly, because the computer isn't robust enough to notice when they are not.

Knurled and Alfa Driver:

Understood. I know this as I was a tech for 12 years. I just never heard of cleaning a cat until this evening. She was a little startled by my reaction (probably the look on my face). 

So far I've seen videos using soap and water, lacquer thinner, and sodium hydroxide. None of the videos make anything other than specious claims of no more fault code. One talks of removing the ash resulting from combustion. Correct me if I'm wrong but that would be from oil and if you're getting oil ash you have other problems. Another pointed out the lead flakes rising in the soap!?! Others talk of putting a gallon of lacquer thinner in a half tank of gas and driving it hard for a while.

When I last worked as a tech BG was always trying to get us to up sell their various injector and engine cleaner chemicals. I would think that if there was half a chance of this working they'd have a kit for it.

In reply to Knurled. :

So much for making generalities... 

(Still, the "catalyst cleaning" thing- there's only so much one can do with actual catalyst damage)

In reply to vwcorvette :

Unless a car is burning a LOT of oil, there's no ash to deal with for gasoline.  There are combustion deposits that can be cleaned....  but not sure how that relates to cleaning a catalyst.  That goes for lacquer and any ohter additive in the fuel.  Not that it's a bad thing, it's just not really "cleaning the catalyst"...  

And unless someone is getting their gas from airports (where lead is still a thing), there's no lead.

In reply to vwcorvette :

I'm sure BG would, but they seem bound and determined to only sell product that actually works.

Your YouTube stories remind me of the guy who put bleach in his fuel tank to try to clean up the converter or something.  That was fun.

In reply to Knurled. :

Very informative. Thank you. 

Not totaled related but my wife’s 07 Versa was throwing that could off and on for months. Last week it was way down on power and it only threw that code. Stupid me did some google searching instead of actually messing with it(it’s been 90’s and super humid here) and every post said the cat had failed more then likely. It made sense to me at the time as it has 187k on it and does burn oil. I replaced the cat and test drove it after clearing the code. Well a misfire on #4 popped up but no other code. I verified the coil was bad and replaced it. Problem solved. 

So just cause it’s throwing the code doesn’t mean it’s the cat or the O2 sensor. 

In reply to rattfink81 :

Misfires kill converters, though.  That's why active misfires will cause the MIL to actually flash - they want you to stop the engine ASAP before it kills the cat.

Knurled. said:

In reply to rattfink81 :

Misfires kill converters, though.  That's why active misfires will cause the MIL to actually flash - they want you to stop the engine ASAP before it kills the cat.

Very, very, very quickly.  I did it once on my Miata, after cleaning the engine.  Took just a min or two before the catalyst was dead enough.  Lucky for me that it was recalled for another catalyst fault, so I got one for free...