I have diagnostic code P1135 (air fuel ratio sensor heater) on a 2002 Camry with 3.0 engine. Fuel system 1 is operating open loop. I think that the problem is a failed Ox sensor, but I'm not sure. How do I isolate the problem?

Hi you have a bad air/ fuel ratio sensor. On b1
1. Check the heater resistance of the air fuel ratio sensor. The resistance between the two Black wires should be between .8-1.4 ohms.
2. Check for battery voltage supply to the sensor on the Black/Red wire. The Blue wire should have 12 volts key on and get grounded by the computer when the engine is started.
Replace both sensors at the same time. It is very common to get a code for one side and then after it is replaced a code for the other side sensor will set. Anytime the check engine light comes on the C1201 code will set. It indicates there is a code in the engine control computer.
Be careful when replacing the sensor. The oxygen sensors look very similar to the air fuel ratio sensors. The connectors are slightly different but can swap if pressed together hard enough.