odd O2 sensor behavior
Thread Starter
Newbie
Joined: Oct 2020
Posts: 4
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G55, 560SEC
odd O2 sensor behavior
I'm tracking down a rough idle issue and looking on XENTRY at O2 sensors. The upstream sensors seam to work fine (both fluctuate normally ca 80 to 730mV). Right downstream seems to work normally (at my limited knowledge) as well. Steady at 690mV. But left downstream is steady around 100mV or below. What could be the reason for so big difference? Faulty sensor, cat issue? How to troubleshoot it further?
Super Member
Joined: Aug 2018
Posts: 697
Likes: 172
From: Seattle, WA
2019 M5 Comp, 2005 Ariel Atom 2
I would venture a guess that it's more likely a sensor problem, in the past I've seen bad cats cause a fluctuating o2 reading on the downstream sensor that mimics the upstream. It sounds like your upstream sensors are working properly, and the downstream are just used for emissions so will not affect your idle. I'd start looking at other sources for the idle concern. Any codes in STAR? Fuel trims ok? How old are the engine mounts?
Member
Joined: Jun 2016
Posts: 101
Likes: 1
From: Bluffton, SC
2009 W211 E63, 2000 Yamaha R1
I'm guessing you have not gotten any error lights, but I would look closely to the O2 sensor. Mine started with a rough idling too first and then started throwing a code for the upstream sensor. Replaced it and is back to normai now
