QuestionQUESTION: i have a 2000 Toyota MR-2 the codes translate as bank 1 sensor 1 and bank 2 sensor one low voltage heater, i need to know what sensor they are (before or after cat) and which one of the before cat sensors it is that needs replaced. (not even the repair manual tells what one it is)
ANSWER: The codes refer to the sensors in front of the converter. I don't know what they mean by bank 1 and bank 2. This usually refers to the left and right sensors on a V engine, which the MR2 doesn't have. So, you should just have to replace the upstream sensor and be good to go. That business about the low voltage heater makes me think that the computer is sensing that the heater built into the sensor is not working. Make sure that you check the wiring going to the sensor, it might be that and not the sensor itself.
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QUESTION: ok, so i need to replace them, which ones though? there are 2 sensors on the exhaust header, and one after the converter, i dont want to buy the wrong ones and waste $200. if bank one and bank 2 refer to a V-engine, which would have one on each header, then would both the upper ones be bad, or one top and one lower?
Answer I would really love to know why they are using 2 sensors on a four-cylinder engine. It may have something to do with the design of the fuel injection system. I looked through several books and only found one that referred to the fact that there were two upstream sensors. Standard sells them (both the same) as part #SG368, and RockAuto carries them for about $83.00 each. You could buy one and switch them around to see if just one would do it. Then, if you really do need two, just buy another one. These things will pay for themselves fairly quickly. While they are not working your engine runs in what they call the "open-loop" mode. With no feedback to let the computer know what the air/fuel ratio in the cylinders is, the "open loop" mode is designed to purposely run the engine a little on the rich side. This reduces fuel mileage significantly, and shortens the life of the spark plugs as well. I would replace them both, they are the same age and likely to fail at the same time. I'd still like to talk to someone who could explain why they are using two of them, though.
