One problem related to o2 sensor has been reported for the 2001 Toyota Sienna. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2001 Toyota Sienna based on all problems reported for the 2001 Sienna.
2001 Toyota Sienna le, purchased new, started having problems. "check engine" light came on when vehicle had approximately 25,000 plus/minus miles. Under warranty, Toyota dealership replaced the oxygen sensor without a charge. However, during this process, the "beep" signal you hear when locking-unlocking the vehicle with remote key was disappeared. This is also fixed under warranty. The "check engine" light came on again when the vehicle had about 35,000 miles. Toyota dealership said it is due to a dirty vacuum hose, they cleaned it with a charge little over $100. 00. The next day the "check engine" light came on again, this time the Toyota dealership said they need to replace the charcoal canister (parts free, but we have to pay labor--about $100. 00). This thing causes extreme mental distress, time, money, security etc.