ses light-heater circuit

98 ASTRO-ses light has been on for 6 months. when it first came on i went to o'rielly auto parts and was told my problem was prob the main oxygen sensor and if I replaced it the light would go off. i spent $70+ on this and had it put on and the light was still on. so we took it off and put the old back on. the code auto zone gave me yesterday is PO135-MALFUNCTION IN HEATER CIRCUIT FOR OXYGEN SENSOR 1. IS THIS NOT THE main sensor that I have tried? where is this sensor 1 in bank 1? sorry i am a female who is not mechanically inclined!

just wanted to say that, no thanks to anyone here-my ses light is no longer on...problem was fixed!