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Q: 3.3L V6 throwing P0430 and P0157. Is the problem the CAT or the O2 sensor? on 2006 Toyota Sienna

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The van is running fine. The dealership first wanted to replace the exhaust manifold and the O2 sensor and now they want to replace the coverter. Im not doing anything until I am sure what the problem really is. COuld the bad converter be throwing the O2 code or is it a bad O2 probe throwing the converter code?
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I'd focus on the rear O2 sensor. It's easy to check with a lab scope while creating reach/lean mixtures. Bad O2 sensor could cause low cat.converter efficiency.

Thanks. Unfortunately I don't have access to a scope and currently doubting my dealership's ability to diagnose and dont possess a scan tool. Other question can you confirm that sensor 2 , bank 2 on this engine is the rear bank, i.e. towards the rear axle? Thanks again.
Yes, let me explain:
B1S1 = Bank 1 (it's the side of the #1 cylinder) Sensor 1 ( the sensor before the cat. converter)
B1S2 = Bank 1, Sensor 2 - the sensor after the cat. conerter
B2XX = the opposite bank
So B2S2 is the Bank 2 Sensor 2 - the sensor after (towards tail pipe) the cat. converter.
The cat. converter should be covered under warranty. If you have the owner's manual it should have a warranty section, check what it said about the warranty?
How many miles you have in the car?
If you are in doubt with the dealer's ability you should get a second opinion from an independent Toyota shop.

OK, it looks like your converter has 8 years / 80,000 miles warranty, but the 02 sensor not. So if the dealer sure about the converter problem, (and the mileage in the van less than 80K) let them replace it - that's the expensive part anyway. If the code will come back, just pay for the rear O2 - and you get a new converter for free.

Thanks again. Guess I forgot to mention my van has 112k on it already so I am pretty much on my own which is why I hestitate with my dealer. The van has ran fine this way for 6 months now but I am afraid if something else goes wrong I will miss the problem because the check engine lights are always on. I think my best options are to either roll the dice on the O2 sensor or go after in a 2nd opinion. Do you advise against the cheaper universal O2 sensors verses the in kind replacement? Should I only get a Toyota supplied part? Thanks again. RTW
Unfortunately with 112K it's out of the warranty.
I won't use the cheaper aftermarket cat.converter for any vehicle, they never last!
We tried different ones in the past, never again! Waste of money.
If this would be my vehicle that's what I'd do:
since there is a bad rear O2 sensor code in the ECM P0157, I wouldn't worry about the converter code now. Get a new sensor, reset the adaptations and drive it.
Bad rear O2 will cause converter efficiency code since the efficiency measured by it, however bad converter would just throw an efficiency P0430 code, not a P0157.
I hope you get my point.

You are very welcome.
After the sensor replacement ask the shop to reset the ECM adaptations so the computer will adjust to the new (good) condition.
Let us know what happened, please, so others can learn from it too.

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