This is an FYI for the community on changing the downstream O2 sensor. There is nothing out there that I could find about the 2003 model. There is a video for the 2005 model which has the pig tail location under the dash. After pulling the carpet up and finding nothing, I scoped the body hole to see where the pig tail went. Toyota must have figured the location was bad in the 2003 and maybe 2004 model because it is located under the seat. You have to remove the seat, 4 bolts, then the amplifier, 3 bolts, and lift the carpet up by the front frame of the seat bracket and its tucked in the corner by the center console. To install, you run the O2 sensor under the carpet and through the access hole then plug it in. Hope this helps some people in the future.