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I got a check engine light with code P0031 - Heater Control Circuit Low (Bank 1 Sensor 1) which sent me on a hunt for info and how to fix it. Here's what I've pulled together and should help anyone else with the same issue. Our cars have a sensor that is downstream of the catalytic converter and one that is upstream, also known as an air/fuel ratio sensor. Bank 1 is located on the passenger side of the car. Therefore Bank 1 Sensor 1 is going to be located pre-cat on the passenger side of the car. Heater Control Circuit Low refers to a failure of the heater circuit that heats the oxygen sensor to help get it up to operating temperature when cold. Your best bet with this failure is to replace the sensor with a new one. I ordered mine off of Rock Auto for $116 CAD part number 2349120.
Start by taking off the front passenger side wheel and put the car on a jackstand.
Remove the push-pin plastic rivet circled here and pull the skid plate down to expose the O2 sensor.
Head into the engine bay and unplug the old sensor from the harness. The plug is near the rear of the engine bay near the strut tower.
Unscrew the sensor using an O2 sensor attachment for your socket wrench which can be bought for around $15 and is worth it in this case and then unplug these connectors from the old sensor cable in the engine bay.
Here's what the new sensor looks like. It's blue as opposed to yellow for some reason but the sensor part looks right.
Now connect the new sensor in the engine bay and feed it down through where the old sensor was. Screw the sensor into the socket using your wrench and then clip the connectors back into their spots in the engine bay. Screw the sensor in first or you'll get a wire that looks like mine does in this shot - curly
Button her all back up the way you found 'er and fire up the engine. If your CEL is still staring at you reset your ECU. Everything should be fixed now. If it isn't you've either done something wrong or you didn't really have a malfunctioning sensor and something is probably seriously wrong. Otherwise you're done!