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Old 11-20-2002, 11:04 PM   #1
wistful
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Member#: 745
Join Date: Jan 2000
Location: Royal Oak, MI
Vehicle:
2004 STi
Java Black Pearl

Default is the second o2 sensor necessary?

What were to happen if I were to just remove it? I mean, I already have a cat inefficiency code as we speak? Woudln't it just be the same? The car wouldn't totally spaazzzz would it?

Don
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Old 11-21-2002, 03:14 AM   #2
HndaTch627
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Default

you'd have a rear o2 sensor malfunction code instead
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Old 11-21-2002, 10:10 AM   #3
wistful
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Default

so what are the performance ramifications behind that? I mean.. would my car run ok? or would it go into limp mode?

Don
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Old 11-21-2002, 11:41 AM   #4
Julian
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The second O2 sensor is for OBD-II regulations, and mostly to let you know of the degrade/demise of your cats. It wouldn't limp.
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Old 11-21-2002, 11:42 AM   #5
Keith Cournoyer
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Location: Somerville, MA
Default 2nd O2 Sensor

I ran about 150+ miles with the 2nd O2 sensor removed, constant CEL, but no performance difference. The sensor is a waste of $150 if you ask me! I heard that the front 02 is the one that's important? Keith
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Old 11-21-2002, 02:59 PM   #6
whitemr2
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stealth silver

Default

As others pointed out, it's just to monitor performance of the cat. It has no effect on performance (although, I can't rule out the possibility that the ECU MAY alter its maps if it thinks it has a bad catalytic convertor).

If you want to get rid of the check engine light, take the wires that used to run to the second sensor and connect them to the primary sensor (just like you'd connect an A/F gauge). That should appease the ECU.
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Old 11-21-2002, 04:30 PM   #7
kturner
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Default Careful

about wiring them together. The front is (at least on some cars) a 0-5 V signal whereas the rear is a 0-1 V.
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Old 11-21-2002, 07:25 PM   #8
EvasionOfTruth
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WRB SPB Edition

Default Re: Careful

Quote:
Originally posted by kturner
about wiring them together. The front is (at least on some cars) a 0-5 V signal whereas the rear is a 0-1 V.
You are correct I believe it is on 2000 and up.
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Old 11-21-2002, 07:35 PM   #9
SubaruStu
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Default Re: Careful

Quote:
Originally posted by kturner
about wiring them together. The front is (at least on some cars) a 0-5 V signal whereas the rear is a 0-1 V.
You wouldn't want to do that anyways. The ECU monitors the
switching frequency of the sensors. The front switches far more
frequently to adjust for driving conditions, as a result the rear
sees a more "constant" stream and consequently switches
(rich/lean that is) far less. When you cat starts to go, the
second sensor starts switching more frequently. At a certain
threshold of % frequency of the front, the CEL is triggered.

What most electronic fixes do via a resistor and capacitor, is to
keep the switching frequency sufficiently slow as not to trigger
the threshold limit.

Here's a good link to describe how the ECU and OBD-II works
for these things:

http://www.autoshop101.com/forms/h46.pdf
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Old 11-22-2002, 12:38 PM   #10
whitemr2
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Default

Thanks for the clarification! My experience with this is on an OBD-I Toyota with dual sensors, which I now realize is a pretty unique application of the 2 O2 sensors (it basically ignores the second).

I didn't realize the output voltage could be different with different sensors.
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