I have a 2003 Toyota Camry, I4 engine, about 100,000 miles, recently "check engine" light came on. Got the OBD code P0420 at AutoZone, and the possible cause, from AutoZone printout, could be:
1. Engine misfire or running condition
2. Large vacuum leak
3. Engine oil leakage

The car did not have any major service except for routine engine oil and transmission oil changes. The spark plugs looked better than I expected, considering 100K milage (slightly worn tips, light yellow color and no excessive deposit), but I changed anyway. The oil level maintains constant so I don't think oil leaking is the cause, neither.

This lead to only possibility of "large vacuum leak". However, I don't have any experience on this. If this is the case, what kind of symptoms you would expect to see and how to check and fix the problem? Any inputs are greatly appreciated.

 

This seems to be a common problem with Camrys. I have read where they replaced the cat. converter and the O2 sensors.

Hang in there, I think John (Tow_Guy) has had a hundred Camrys

 

Do you hear any hissing noises under the hood? That would be the first sign of a vacuum leak. It can be as simple as a vacuum hose that has popped off, cracked, or a gasket on the intake manifold for example that has fallen apart.

 

Only on my second Camry, just seems like a hundred because they last so long. My inclination from that code would be that the cat is shot. The definition SHOULD be "Catalyst System Efficiency below Threshold." Not sure how AutoZone came up with what you said the printout says. Could very well be an O2 sensor since that's how the computer would determine the cat "efficiency". Used the right spark plugs, right? Probably those twin electrode expensive ones?

I have yet to replace a cat on ANY of my Toyotas, so I would be a little leery of jumping to that conclusion, especially considering the cost. Probably time to bite the bullet and take it to a good garage where they can put the full-system scanner on and see what's cooking. Whether you choose a dealership or independent is up to you, but any competent facility with a good scanner shoule be able to properly diagnose it. At any rate, if it needs a cat I would probably not buy the genuine Toy part if I could avoid it; don't even want to THINK about how much that baby would be.

 

If it is the cat and you don't have any emission laws, you can cut it out and replace it with a straight pipe. Not the most environmental friendly ordeal, but many project cars with modified exhausts do this.

 

I believe he lives in NY, and they do have inspections there.

 

PO420 is a catalyst efficiency below threshold code. I've been involved in lengthy discussions with both automotive engineers and experienced technicians with high tech diagnostic tools regarding this code. These discussions went into the nitty gritty details of this code and how the engine computer determines that the converter is going bad and the bottom line is that you will need to have the converter replaced.

100k miles isn't out of the realm of possibility of the cat going bad from normal operations but I have also seen them last twice this long. When you have it replaced it would be a good idea to have the engine checked out to be certain poor combustion efficiency isn't contributing to the cat failure.

 

Actually the AutoZone scan did diagnose the problem as "Catalyst System Efficiency below Threshold" but it further pointed out possible cause of the problem which I posted earlier.

So I guess it's time to replace the Cat!?

 

no one ever checks the vacuum lines. they get hard over the years and start leaking/cracking. not a big leak, but a lot of little ones= one big one. i like to start simple. check ALL th vacuum lines at both ends. if they pull off easily, cut off about 1/4 inch and re-install. if not long enough, buy new ones. cheap fix even if that is not the problem. start small work up to the big bucks!