'99 RX300 had a check engine light and ran rough when first started cold. Went to local Autozone and had them read the codes for free. I searched 'Toyota engine code P1135' on google and found that it was the pre-heat for the bank 1 sensor 1 O2 sensor. This is the sensor in the exhaust manifold right near the firewall(not easy to get at) First I disconnected the sensor wiring and measure the resistance across the two black wires. I got an open loop reading and compared to the Bank 2 sensor that was 10 Ohms. So I knew it was bad. Getting to the sensor is not easy but you can see the electrical connector through the intake manifold from the top of the engine. Helps to have small hands. To get the sensor out of the exhaust you will definately need an O2 socket. Soak with a lubricant for a few days, use a plumbing torch to heat the exhaust pipe around it. But.... it still won't budge. Add a lenght of pipe to the wrench and it will finally go. Main point is... you definately need the right tools for this job. The O2 socket is a must.

 

The socket or closed crowsfoot is 22mm in size ...and a sixteen inch swivel head ratchet is also handy.

And yes, the resistance is zero or infinity when it's in an error state.