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Ron Z.
Ron Z., - Toyota Tech -
Category: Toyota
Satisfied Customers: 18453
Experience:  18+yrs experience. State Inspector and Toyota Diagnostics
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Toyota Sienna: I have a 2003 Toyota Sienna that failed emissions

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I have a 2003 Toyota Sienna that failed emissions inspection with code P0420 (catalyst system efficiency below threshold bank 1). The catalytic converter, alternator, manifold and O2 sensors have been replaced but it again failed inspection today. What should I do now?
Hello! Welcome to the site! Thanks for coming! I'm Ron Z. I'm here to provide as much information and insight as I can, to best answer your question.

I'm sorry the Tech you requested was not available to assist you today. It appears Skyvisions (great Tech by the way!) is currently "Offline". Hopefully I can be of some help in his place...

Just a few questions...

When you say the "catalytic converter was replaced" - can you tell me which one was replaced? It's location? And when you replaced this, what brand name converter was it replaced with?

When you say the "manifold" was replaced- was this an exhaust or intake manifold? And if it was an exhaust manifold, can you tell me which one was replaced?


Customer: replied 3 years ago.

UPSTREAM CATALYTIC CONVERTER had rusted thru and was replaced with a new one. Both intake and exhaust manifold were replaced with certified used ones.

Ok. What I'm trying to get at here is, on this vehicle, the P0420 is a very common and straight forward code pointing to a fault with the Warm-Up Converter for Bank1. This converter is located on the side of the engine closest to the windshield and and is built into the Exhaust Manifold. So, if you only replaced one, and it was the front one- it's the worng one. If you replaced the one closest to the widnshield, and it was "certified used" - first, this is Illegal in many States, and second... usually never solves the problem. If the converter that was repalced was the correct one, and it was a "universal" (the old one was cut off and the new one welded in place), again, this doesn't meet Toyota-specs and again, usually never solves the problem. I'm just trying to make sure you 1. Replaced the correct item 2. Replaced it with a Toyota-spec part.

Here's the location:

Here's what the correct one looks like:
Customer: replied 3 years ago.

Will take diagrams and replies to mechanic that did the work and find out for sure if he had the right parts and will contact you again after he sees this. Thanks.

Sounds good. Again, if the exhaust manifold WITH converter (the 2nd image I sent) on the CORRECT side of the engine WAS replaced... but it was "used" - this doesn't solve the problem. AND, like I say, in MANY States... Illegal! I think you'll find if you replace the correct part with the correct version, you'll be just fine. I've seen this many many MANY times. It's a very common fail item on these vehicles.

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