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I have 2002 Sienna XLE van. I got engine check code P0420 which says "Catalyst system Efficiency below threshold (Bank 1)." So, I bought CATACLEAN from Amazon. I have already mixed this cleaner liquid when gas tank is about 1/4th full and poured 12 oz. of liquid. Drove the van for 15 minutes before I filled up gas tank. I have repeated this for 2 times and 3rd time is going on. But I don't see engine check light going off and it is still on. What should I do? Please advise. Thanks.
 

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I have 2002 Sienna XLE van. I got engine check code P0420 which says "Catalyst system Efficiency below threshold (Bank 1)." So, I bought CATACLEAN from Amazon. I have already mixed this cleaner liquid when gas tank is about 1/4th full and poured 12 oz. of liquid. Drove the van for 15 minutes before I filled up gas tank. I have repeated this for 2 times and 3rd time is going on. But I don't see engine check light going off and it is still on. What should I do? Please advise. Thanks.
You either need O2 sensors, A/F sensors (assuming the '02 uses A/F sensors the way my '06 does) or a new cat (really, the entire exhaust manifold and cat, because they're all one-piece. If you take it somewhere, they WILL tell you that you need a new cat. New cat typically will set you back at least $1k. All 4 Denso sensors will set you back about $650. The sensors might fix the problem but, if you have to replace the cat, I would replace the sensors at the same time to save on future labor.
 

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You either need O2 sensors, A/F sensors (assuming the '02 uses A/F sensors the way my '06 does) or a new cat (really, the entire exhaust manifold and cat, because they're all one-piece. If you take it somewhere, they WILL tell you that you need a new cat. New cat typically will set you back at least $1k. All 4 Denso sensors will set you back about $650. The sensors might fix the problem but, if you have to replace the cat, I would replace the sensors at the same time to save on future labor.

Could be as simple as a clogged air filter. Several on another thread suggested that, so I tried it. Popped in a new filter and the code went away and has not come back.

A new PCV valve has taken care of it for others.
 

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Could be as simple as a clogged air filter. Several on another thread suggested that, so I tried it. Popped in a new filter and the code went away and has not come back.

A new PCV valve has taken care of it for others.
That's certainly the cheapest, easiest fix! Actually, that should probably be step two for all car problems... Step one, do you have gas? Step two, have you changed the air filter in the last 9 months?
 

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Oh, don't get me started on that one!

And don't ask! :D
Same! I picked up a '63 Rambler one time and took it for a test drive down the low-slope downhill street. At the bottom of the street, the car died. Unsure of the issue, I pushed the car half the way back up the street to the driveway. My The father of my then girlfriend/now wife came home and asks, "Did you check if it had gas?" Gauge read 1/2 tank. He added a gallon and it started right up.
 
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