What would cause downstream o2 sensor voltage low? | FerrariChat

What would cause downstream o2 sensor voltage low?

Discussion in 'Technical Q&A' started by 24000rpm, Jun 16, 2018.

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  1. 24000rpm

    24000rpm F1 Rookie

    Aug 31, 2012
    4,649
    China and California
    #1 24000rpm, Jun 16, 2018
    What would cause downstream o2 sensor voltage to be low, other than o2 sensor itself is bad?

    I understand that if the upstream o2 sensor voltage is high or low, it could possibly mean that the o2 sensor itself is good and the combustion got a problem.

    But what about downstream? Is there any scenario in which the o2 sensor itself is good and a low or high voltage indicate something else is wrong?

    My 360's right-hand downstream o2 sensor is hoovering 0.07v --- 0.85v, most times around 0.1v. It gives a CEL saying voltage low.
     
  2. flash32

    flash32 F1 Veteran

    Aug 22, 2008
    5,695
    Central NJ
    Full Name:
    Dominick
    #2 flash32, Jun 16, 2018
    Oil on sensor , bad connection on sensor, exhaust leak before sensor, or bad sensor

    Sent from my Moto G (4) using Tapatalk
     
  3. 24000rpm

    24000rpm F1 Rookie

    Aug 31, 2012
    4,649
    China and California
    #3 24000rpm, Jun 16, 2018
    so nothing really wrong with engine conbustion or catalytic converter (other than a leak)?

     
  4. flash32

    flash32 F1 Veteran

    Aug 22, 2008
    5,695
    Central NJ
    Full Name:
    Dominick
    #4 flash32, Jun 16, 2018
    Look at upstream sensor ..the voltage should go up and down ..then compare it to the other upstream sensor on the other bank .. also check your short and long term fuel trims

    Once you check all that and everything looks good i think you can assume a sensor issue (minus leaks)

    What program are you using to check voltage at o2 sensor ?

    Sent from my Moto G (4) using Tapatalk
     
  5. thorn

    thorn F1 Rookie
    Silver Subscribed

    Aug 7, 2012
    3,322
    Tallahassee, FL
    #5 thorn, Jun 16, 2018
    Start by checking the sensor with a meter. No sense in shooting in the dark.
     
  6. 24000rpm

    24000rpm F1 Rookie

    Aug 31, 2012
    4,649
    China and California
    #6 24000rpm, Jun 17, 2018
    do you mean check voltage? or resistance?
    I only monitored the voltage in real time and it usually is around 0.1v , occassionally over 0.45v.

     
  7. 24000rpm

    24000rpm F1 Rookie

    Aug 31, 2012
    4,649
    China and California
    #7 24000rpm, Jun 17, 2018
    i have the leonardo to see voltage.
    front lambda changes quickly with my throttle change, and RH upstream lambda is behaving similar to LH, so I assume its pretty healthy.
    I am ignorant, I don't know how to see long term and short term fuel trim in a Leonardo......
    I don't know what parameters to look at.

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