Toyota Repair: sienna catalytic converter problem, emission control device, nitrogen oxides

Question
QUESTION: for the last 40k miles the check engine light has gone on and off and the dealership has determined it's the catalytic converters (two?).  cost is $2900 to repair.  our 2004 sienna has 160k miles on it.  my question to you:  is it dangerous to ignore this and just ride the van until it dies on us?  one of the service reps told us they can actually get really hot and start a fire.  our inspection isn't up until september so we were thinking of ignoring it but i wanted someone's knowledgeable opinion on this.  i believe running it this way can cause damage to the engine but how do i know the damage isn't already there, in which down the road it may cost more than the $2900.  so we're not sure we want to sink money in to the van.  we're disappointed.  we spent more money to buy a toyota versus a dodge van and had been fairly happy with the quality but oh well....  would appreciate your answer.  thanks.  sonia

ANSWER: Hello do you have the diagnostic codes from the dealer, your invoice should list them. If not I'll have to assume that it was catalityc converter codes. The codes mean that the catalityc converters have lost the ability to remove certain emissions from the engine and have deteriorated, I have not seen any of them cause a fire because of this malfunction.   

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QUESTION: Thanks for clearing up the danger element (can it potentially cause a fire?  my understanding from your post is 'no.').
Now, in your opinion, with the light going on and off over the last 40k miles, is it possible that damage to the engine may already be occurring?  We're just concerned that even if we sink $2900 into the van that we might still be looking at engine damage in addition?
Thank you so much!!
Sonia

Answer
The catalityc converter is an emission control device, it's sole function is to reduce harmful exhaust gases such as carbon monoxide, hydrocarbons and nitrogen oxides, when it becomes inefficient it loses it's ability to reduce these gases into water vapor and reduced emissions, this does not cause driveability issues or engine damage, in extreme cases the converter can internally disintegrate and cause an exhaust restriction and a loss of power, since the check engine light goes on and back off it seems the converter is in the early stages of malfunctioning. Sometimes this on/off condition can also be caused by failing oxygen sensors but I would need the original trouble codes from the dealer to be absolutely sure. What I would suggest, if the dealer didn't give you that information is to go to an Autozone, O'Reilly or Kragen autoparts store and have the computer scanned, they do this at no charge, then reply back to me and let me know what the diagnostic trouble code numbers are.