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Hi Peter,
I thought the o2 sensor would "see" the rich mixture and then tell the ECU to compensate for it. The last three codes I pulled were 231, 113, 221 all fuel related.
Yes, that is exactly what should happen. The oxygen sensor creates the higher voltage (anything above 0.5V) when it sees more fuel, or a rich mixture. The computer's normal function is to lean out the mix in small amounts until the sensor reads something it deems lean, well under 0.5V. That is the cycle when all is well.
But, when the ECU, for instance, sees a lean condition because of a vacuum leak or inoperative injector, it may be unable to increase the fuel a reasonable amount to re-establish an average correct mix. It sets a code when the trim attempts begin to fail, and, then when the computer is still unable to compensate, it lights your CEL and gives up trying to match things, defaulting to a rich "limp home" mix that you see as a steady 0.8V when you look at it.
Reset the computer (pull the 25A blade fuse momentarily) then monitor the sensor voltage as you warm the car up from cold. Use your senses to try to establish if it goes lean or rich before the first codes are set. You may not get your 113 back until you drive it some, but between your senses, the meter readings, and if needed, a look at the spark plugs, you should be able to determine which way it is headed.
The knock sensor code may be a clue (like lean rather than rich) but it is not part of my experience. The point is, once the computer has turned off its brains and set its CEL, the oxygen sensor cycle across stoich is ended.
A better heater test is to check resistance of the heater about a minute into first running the car from cold. Measure it as soon as you disconnect its plug, and watch the resistance fall, indicating a hot element cooling. That checks the entire circuit.
--
Art Benstein near Baltimore
It may be that your sole purpose in life is simply be kind to others.
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brand new bosch o2 sensor not working [200][1989]