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O2 sensor

Tiny
ZEMORZEMOR
  • MEMBER
  • 2000 MAZDA PROTEGE
  • 1.6L
  • 4 CYL
  • 2WD
  • MANUAL
  • 190,000 MILES
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?
Saturday, March 17th, 2018 AT 7:17 AM

9 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
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
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Saturday, March 17th, 2018 AT 7:46 AM
Tiny
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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.
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Saturday, March 17th, 2018 AT 7:50 AM
Tiny
ASEMASTER6371
  • MECHANIC
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Very little flow at idle.

The sensor is reading normal.

Do you have a code or some malfunction?
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Saturday, March 17th, 2018 AT 7:52 AM
Tiny
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No codes.
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Saturday, March 17th, 2018 AT 7:52 AM
Tiny
ASEMASTER6371
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Good, why are you checking?
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Saturday, March 17th, 2018 AT 7:53 AM
Tiny
ZEMORZEMOR
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  • 486 POSTS
Because my car was misfiring leaking coil. I want to make sure my catalytic converter did not melt.
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Saturday, March 17th, 2018 AT 7:54 AM
Tiny
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Based on those readings, you are good to do.

Roy
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Saturday, March 17th, 2018 AT 8:02 AM
Tiny
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Thank you have a good weekend. Five stars.
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Saturday, March 17th, 2018 AT 11:49 AM
Tiny
ASEMASTER6371
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You are welcome.

Thank you.
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Saturday, March 17th, 2018 AT 11:50 AM

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