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Scope testing an oxygen sensor

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1 year 10 months ago #56336 by Onuk
I think that the 1 to 5 hz signal we watched while doing the oxygen sensor test was produced by the PCM. Does frequency out of range indicate that the PCM is not able to control oscillation or that the sensor is lying? How can we distinguish them?

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1 year 2 months ago #59510 by shotgun
my thinking is that the pcm provides heater voltage to get the O2 sensor up to operating temperature and the O2 sensor creates the signal that changes from 450mv plus or minus (100 to 800mv) in response to changes in fuel trim in a healthy system this all happens at a frequency between 1 to 5Hrz. hope im not leading you down the wrong path

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1 year 2 months ago #59511 by Onuk
Replied by Onuk on topic Scope testing an oxygen sensor
First of all, Thank you for your reply. To review my knowledge: STFT is controlled by PCM. The STFT's primary job is to keep the O2 sensor slightly above and below stoichiometric. While performing this job: Is the PCM controlling the mixture , (lean / rich) at a frequency of 1-5 hz or is the frequency generated by the o2 sensor? Sorry for my English.

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1 year 2 months ago #59520 by shotgun
your welcome,
i believe the O2 sensor signal frequency indicates how often the PCM is making rich/lean changes to STFT. what we see as highs and lows on the waveform are fuel trim changes. how often the PCM makes these changes is seen as frequency.
Why is there a range of 1-5Hz? engine load, hot/cold, manufacturer, response time of the vehicle components who knows?
The following user(s) said Thank You: Onuk

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