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In your 2004 Toyota Sienna, the location of bank 1 sensor 1 is at the bank of cylinders that include cylinder #1, which on your van is the rear or closest to the firewall bank of cylinders. This sensor is approximately the size and shape of a spark plug and extends into the exhaust stream of the engine. Its purpose is to analyze the oxygen levels in the exhaust, allowing the engine to adjust the fuel usage for optimal performance. If your vehicle has a malfunctioning oxygen sensor, it may experience irregular idling or rough sounds. A defective oxygen sensor can impact various engine functions such as timing, combustion intervals, and overall performance, potentially leading to stalling or sluggish acceleration.
The sensor 1 for bank 1 in the 2004 Toyota Sienna can be found on the exhaust system, positioned both before and after the catalytic converter.