P0420 Code - Tried Everything :-(

[abstoler]

Hi all,

First off, thank you to those who post replies. I really appreciate these forums. I have a 2000 Toyota Camry with 175 K. Last year the check engine light came on. Code was P0420 Catalytic Effeciency. Took it to one mechanic...he said the downstream O2 sensor was going. Didn't have to get it inspected yet, so I just let it go. When inspection time came around I took it to a different mechanic (foreign car specialist). They said O2 sensors read fine and within range, but that both front and rear cats were practically dead.

I sucked it up and decided to replace the cats, but not without a third mechanic's opinion. The last mechanic, who used to be head mechanic at a Toyota dealership, said the same thing as the last one: Cats were dead, O2 sensors were fine. To the tune of $950 he replaced both cats and reset the OBD system. The check engine light was off for about 300 miles, then came back on.

I pulled the spark plugs and they look fine (two pronged, gapless...1 year old). Gas cap fits on fine. No leaks in air hose. Air filter is fine. I'm assuming they checked the MAP sensor. Filled the tank with premium gas. I'm getting great mileage (30-35 mpg). RPM's have not changed since I bought the car at 97 K miles. Check engine light is still on.

The only other thing I can think of is that when I first got the car there was a problem with an O2 solenoid sticking. I have no idea what this is, but I assume it opens the airflow when the system requests. In any case, they replaced it. Also had a flex joint burn off on me, and that was replaced.

Please help guys...I'm stuck and this thing needs to get inspected.

[z27ls3]

the guy you let fix for $950.00 used OEM cats ?
if not you may need genuine cats, aftermarket ones seldom
work.

[abstoler]

front one was a genuine toyota replacement. the rear was after market. It was soooo expensive. He said that the front one was doing most of the work anyway, so an aftermarket on the rear should be fine.

[Stillrunning]

Not a bad article here:
http://www.aa1car.com/library/p0420_dtc.htm

I'm surprised that "The last mechanic, who used to be head mechanic at a Toyota dealership, said the same thing as the last one: Cats were dead, O2 sensors were fine." did not do an exhaust gas analysis before having you replace the CATs. When paying mechanics you pay for knowledge/experience and the cost of their test equipment, not their baseless assumptions.

[abstoler]

Thanks for the link. I'll call the dealer tomorrow to ask about the "reflash" option. As for the value of the mechanic...I've left out a bit of information. I'm a student on the go, and the third mechanic actually lives in a no-emissions testing county, so he doesn't have the equipment. But the second mechanic that I took it to DOES live in an emissions-testing county. They tested the emissions and declared the cats dead.

I suspect the cats died because oil contaminated them. I'm burning about a quart of oil every 3000 miles.

In any case, the third mechanic did test what he could, which included the O2 sensors and checks for any air leaks. Positive checks on those points suggest the cats were dead.

[Nark]

Last time I couldn't pass smog test was due to 80+% clogged converter. This is 1986 Cressida w/ 210kmi. and it drink just as much motor oil as your. It's OBD1 so there's no down stream O2.
Did you get a chance to look at your old converter? Did you change out both O2? It need to be change about 50k mi. disregard the condition.

[abstoler]

Like I said, both O2 sensors checked out fine. Cats were probably clogged, but they were both changed.

[BMR]

Get the error codes read; it could be something totally unrelated to replacing the cats.

[abstoler]

Had the code read as soon as the light went on. The ONLY code that it is reading is P0420. No other codes.

[z27ls3]

the front converter(S) are sometimes the manifold, so oem is only choice but lower cat can be swapped to non genuine part. I have seen the lower converters "just barely" pass emissions right out of the box. I still maintain that the shop the sold you the $950.00 repair needs to make it right. you may need a OEM lower cat.

[ghettosled]

ive been running aftermarket cats for about 5 years now without an issue. i agree with the mechanic about the second cat not being a problem because it isnt monitored. you can probably straight pipe it and the computer wouldnt know. what i would do at this point is replace the O2 sensors. maybe they are starting to have problems or the wiring is getting sketchy. since the old sensors were swapped over, replacing them shouldnt be too difficult to tackle yourself.