What is it? O2 sensor?


Old 07-15-03, 11:39 AM
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What is it? O2 sensor?

1996 Nissan Sentra 1.6L stand.transmission----There is a control or sensor that that sticks out of my catalitic converter.It has 3 wires going to it.The wiring harness goes towards the rear of the car and not forward to the engine.Thanks ahead of time
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Old 07-15-03, 11:47 AM
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Yup, sounds like the O2 sensor.
Old 07-15-03, 12:40 PM
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Your car actually has 2 O2 sensors.

The upstream (closest to the engine) sensor tells the PCM how much O2 is in the exhaust gas. The PCM uses this information to adjust the air/fuel mixture to minimize emissions.

The downstream sensor (typically just behind the convertor, sometimes in the rear third of the convertor itself) is used as a catalyst monitor. The PCM compares the upstream & downstream signals to ensure catalytic convertor function.

If the downstream signal is similar to the upstream signal, the catalytic convertor is not functioning & the PCM turns the "check engine" light on.
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