not for altitude, but to keep the air:fuel mix the same, which changes as you go up in altitude.
The computer uses the oxygen sensor input to regulate the fuel mixture, which is referred to as the fuel "feedback control loop." The computer takes its cues from the O2 sensor and responds by changing the fuel mixture. This produces a corresponding change in the O2 sensor reading. This is referred to as "closed loop" operation because the computer is using the O2 sensor's input to regulate the fuel mixture.

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