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Old 05-25-2008, 08:11 AM   #1
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Question How to identify O2 sensor wires? How to tap them? How to read them?

I'd like to tap an O2 sensor's wires and hopefully use a DMM to get a relative idea of A/F ratio while driving. I'm pretty sure mine are narrowband.

The normally sensible engineers at GM decided that my pre- and post-cat O2 sensors should have the same color wires and be in the same bundles. Besides physically tracing the wires or using a tone generator & probe, how do I tell them apart?

Once I find them, I assume I can just carefully tap them with a scotch-lok quick splice. I won't need to cut and interrupt them to put my meter in series, right? I don't want to interfere by measuring...

Once I have my DMM hooked up, I'm pretty sure I'll have to look at voltage. Would a higher reading mean richer or leaner? A little googling makes me think that higher voltage means richer ratio.
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Old 05-25-2008, 08:21 AM   #2
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Yes- a higher voltage (above 0.45v) usually means rich.
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Old 05-25-2008, 09:23 AM   #3
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Thanks, that's one question answered.

Also, they have three or four wires (I'm working off the ECM pinout here, I was under the truck looking at them earlier but I don't want to get dirty now) each. One is described as "low" and the other "high", and a third is the heater, and a fourth is "low reference". Which do I probe, the low or the high? Or, do all these wires mean I have wideband sensors (and then what does that mean I can additionally do)?
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Old 05-25-2008, 09:50 AM   #4
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heated O2 sensors are not wide-band O2 sensors. if you tap into the O2 sensor, it's going to give a signal that flips rich/lean several times a second... very hard to read. I've known people that put a A/F gauge on a regular O2 sensor and it was pretty much useless except as a flashing light. if you want a readable gauge, get a wideband O2 sensor and gauge.
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Old 05-26-2008, 06:07 AM   #5
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Drat. Wideband sensors are expensive.

There is a LED bar graph DIY gauge that I found after I posted this, which appears to be very popular, but I need to find a little more info on building it or just suck it up and buy one.
http://autospeed.com/cms/A_0217/arti...popularArticle

So, what do "low" and "high" mean?
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Old 05-26-2008, 09:12 AM   #6
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What kamesama said. I think without a wideband sensor you won't be getting useful information.
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