o2 sensor

2000 MAZDA PROTEGE
190,000 MILES • 1.6L • 4 CYL • 2WD • MANUAL
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ZEMORZEMOR
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The downstream o2 sensor reads lean 0.1 V at idle and when driving the car it read 0.7 V. The upstream oscillate normally. why it reads lean at idle?
Mar 17, 2018 at 7:17 AM
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ASEMASTER6371
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Good morning.

The downstream O2 has only one job, that is to monitor the catalytic converter. The voltage will drop a bit at idle and raise a little when running but should always be stable and not varying like the front sensor. if it does, then the catalytic converter is bad and needs to be replaced.

Roy
Mar 17, 2018 at 7:46 AM
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ZEMORZEMOR
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The voltage at idle or high rpm are study, but there is a huge difference between idling and high rpm. why is it lean at idle? high rpm about 0.6 volts and straight line at idle and near 0 volts and study line.
Mar 17, 2018 at 7:50 AM
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ASEMASTER6371
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very little flow at idle.

the sensor is reading normal.

do you have a code or some malfunction?
Mar 17, 2018 at 7:52 AM
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ZEMORZEMOR
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no codes.
Mar 17, 2018 at 7:52 AM
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ASEMASTER6371
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Good, why are you checking??
Mar 17, 2018 at 7:53 AM
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ZEMORZEMOR
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because my car was misfiring leaking coil. i want to make sure my catalytic converter did not melt.
Mar 17, 2018 at 7:54 AM
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ASEMASTER6371
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based on those readings, you are good to do.

Roy
Mar 17, 2018 at 8:02 AM
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ZEMORZEMOR
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thank you have a good weekend. Five stars.
Mar 17, 2018 at 11:49 AM
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ASEMASTER6371
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You are welcome.

Thank you.
Mar 17, 2018 at 11:50 AM