How many o2 sensor does the 2005 Toyota Sienna have?

The 2005 Toyota Sienna comes with four O2 sensors on the exhaust. There are two that are located before the catalytic converters and two that are located after them. These sensors are there to measure the exhaust gasses from Your vehicle to make sure that they are in the specified ranges. They can send signals to the ECU to either increase or decrease the fuel to keep the vehicle operating in the correct range. When You have a failed sensor You will usually notice that Your van runs rough and may be running too rich. Usually You will also get a check engine light at Your dash that will let You know that You need to check the O2 sensors and replace them if they are damaged.