A/F sensor part #

[reefmkr]

Hi everyone,

I have CEL with p1135 bad Bank 1 Sensor 1 on my 2001 Sienna. I'm trying to order A/F sensor but don't know which part number to order. I get confuse about pre cat front, pre cat back and post cat. I assume its pre cat back but I want to make sure I'm ordering right part. Can someone help me with the part number and maybe place to order (cheaper the better). And what brand should I get denco , walker, or bosch?

Thanks in advance