O2 sensor fell out

Joined
Dec 25, 2002
Messages
3,593
Location
Outside smalltown, IL
Of late my 2000 4Runner has been making some rattling exhaust noises. I figured it was a heatshield or something else non critical on the exhaust system and I hadn't gotten around to checking what might be causing it. So yesterday I'm driving to work and the exhaust gets noticeably louder. I get to work and poke my head under to see the secondary O2 sensor flange empty and the O2 sensor hanging by the wires. Looks like the nuts rusted off since the studs and sensor look just fine. I tied the sensor up with cable ties before I left work at the end of the day and drove home. What surprised me is this - No check engine light. I have to wonder what the point is if the sensor can be tricked so easily, just by having it sit in clean air...
 
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Joined
Jul 12, 2007
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Location
Easton, PA
IIRC the 2nd sensor just makes sure the 1st one is working (probably an oversimplification), so maybe the 2nd one won't trigger a light.
 

JTK

Joined
Aug 14, 2003
Messages
13,747
Location
Buffalo, NY
That sensor only monitors cat function. Funny thing is, I believe that's a way to actually 'cheat' the downstream O2 sensor into thinking the cat is fine (when it reads nothing but air). Joel
 
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Joined
May 7, 2004
Messages
10,910
Location
Nokesville, VA
Many of the O2 sensor cat monitor cheating devices are low-pass filters. I do know that Ford vehicles will test the o2 sensor cat monitor by running the engine rich until the o2 sensor cat monitor signals a rich condition..obviously it can't pass that test if it's just hanging there. A low-pass filter will allow it to pass this test. Also--from what I've seen and read, the catalyst monitor test will only run under specific driving conditions. In some places you could drive for 1000 miles and never drive in the way that it needs you to drive for it to run the catalyst test. (On Ford vehicles, that's between 45-60MPH on level ground for several miles without stopping).
 
Joined
Jul 22, 2005
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NorthEast
Catalytic converter is NOT run all the time. When it is run, it will likely flag the check engine light with the dreaded P0420 code if you had the sensor out hanging there. Specific conditions have to met before the converter test is run by ECU - Vikas
 
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