I recently changed the bank 1, sensor 1 on my 2001 ES300 after getting the P1135 code. I didn't bother to check the heater circuit resistance because the car has about 100k miles and that appears to be the mileage when these sensors fail. The lowest price I could find was from Amazon.com, $132 for a Denso, which is the brand I much prefer. The problem with the Amazon site, though, is it does not know what sensor fits what. When I searched Amazon by application, I had no luck. I went to the Denso site, found their part number for my ES300 and then searched that part number on Amazon, which they had. By the way, near the firewall on the driver's side, there is an 8 or 10 inch, tubular brace that goes from the intake manifold to the block held on by two bolts with 10 mm heads. Taking off that easily-removable brace gave me a lot more room to get to the sensor and its connector.