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Ron Z.
Ron Z., - Toyota Tech -
Category: Toyota
Satisfied Customers: 17954
Experience:  18+yrs experience. State Inspector and Toyota Diagnostics
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Sienna: I have a toyota sienna 2004. I am getting a PO141

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I have a toyota sienna 2004. I am getting a PO141 and a P2238. I understand this means I need to replace the Bank 1, Sensor 2 and the Bank 1, Sensor 1 O2 Sensors. From the best diagram I found, these are both the lower sensors. I would think this means they are the downstream sensors. B1S1 the front downstream sensor and B1S2 the rear downstream sensor. Is this correct? Thanks.
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.

Bank1 Sensor1 is located on the side of the engine closest to the windshield, mounted to the exhaust manifold, before the converter (see image). This sensor is actually an "A/F Sensor" (air fuel ratio) on Toyota vehicles (it's like an Oxygen Sensor, just "smarter" to accomodate Toyota emissions specs). So make sure you replace this with an A/F Sensor and not an Oxygen Sensor. The Bank1 Sensor2 is on this same pipe, but it is mounted to the exhaust AFTER the Converter. Best access to both will be fropm under the vehicle, working from the driver's side upwards. Make sure to check the fuses. Make sure to carefully inspect the electrical connectors and as far up the wire harnesses as you can, looking for any loose, broken or damaged wires. If the visual inspections check ok, THEN replace the sensors.


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Customer: replied 3 years ago.

When I go to buy them they are listed as:


front, upstream


front, downstream


rear, upstream


rear, downstream


Is it correct to assume the A/F Sensor on the manifold is the Rear, Upstream and that he O2 Sensor on the pipe would be called the Rear Downstream?

Is it correct to assume the A/F Sensor on the manifold is the Rear, Upstream and that he O2 Sensor on the pipe would be called the Rear Downstream? - CORRECT! Bank1 Sensor1 (the A/F Sensor) is "Rear Upstream" and Bank1 Sensor2 (the Oxygen Sensor) is "Rear Downstream"

Please remember the website WILL NOT automatically compensate me with a part of your deposit or from your subscription WITHOUT YOUR RATING! Please use the Rating System and *Rate My Service* if the information/advice I supplied has helped you. If you have any more questions, use the "Reply" tab – I'm always happy to answer follow-up questions! Follow-ups are always FREE! Even after you rate! Thank-you!



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