O2 sensor wiring.

On my 1999 C2500 Suburban 5.7 the O2 sensor wires are paired purple and tan and paired purple/white and tan/white. Does anyone know which is the positive from negative ie, the purple or the tan?

Is it safe to check continuity to ground with a multimeter to find the negative one - or can I fry the ECU doing that?

(I'm trying to install an AFR meter and need to know the polarity as it's a one wire hook-up).

They're both sensor wires. One is high, the other low. The black wire should be ground.



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RawbDidIt said:

They're both sensor wires. One is high, the other low. The black wire should be ground.

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What does high and low mean?
I get the ground for the heating element but I need the positive voltage for the AFR meter.

The meter has four wires, a ground and two to the ign switch (one operates the gauge, the other its back lighting) the fourth wire is referred to as ''sensor signal wire'' and is supposed to be connected to the vehicle's ECU.

I had the meter working with the three wires connected to a 12V battery and a flat 1.5V battery (showing 0.8V on a MM) grounded to the negative of the 12V battery and it's positive connecting with the fourth AFR meter and it works as it should.

Should I connect (in parallel) my fourth wire to the purple/white high signal wire?

Those "high" and "low" signal wires are the ones the O2 sensor generates based on the ground and pink (+) wire, and the oxygen levels, and the ECu uses to determine how much fuel to add (or subtract). I also want to say the connections for A and B on the O2 sensor are the heater circuit, but not 100% certain. That's for troubleshooting a suspected bad heater circuit on the actual sensor.

That's basically all I know. I have no idea what you are trying to do, so hopefully someone with more knowledge may chime in...

I've been told to just tee into the high signal wire. But use the one on the other bank that isn't connected to my LPG ECU. Finding it will be fun!

Can I ask what you're trying to do here?

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RawbDidIt said:

Can I ask what you're trying to do here?

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Wiring an AFR gauge for the dash so I can monitor the AFR changes my LPG (propane) system makes during mixed driving.
I'm still messing around with the system and monitoring the changes in AFR will be a help in fine tuning it.

Sensor 2 should be the rear ones (past the catalytic converters). I think that is the way the 5.7 vortec Burb is. (That's how my Burb is.) IIRC from buying parts, there is some variation on this depending on engine and type of truck. I've replaced both rear sensors several times in 7 years, but the front (sensor 1) only on bank 1(driver's side).

Pinger said:

I'm trying to install an AFR meter and need to know the polarity as it's a one wire hook-up

Click to expand...

You should probably use a WBO2 sensor, something like this (0-5VDC) It'll give you a lot better range and feedback.
https://www.amazon.com/s?k=Innovate+3877&ref=nb_sb_noss_2

HotWheelsBurban said:

Sensor 2 should be the rear ones (past the catalytic converters). I think that is the way the 5.7 vortec Burb is. (That's how my Burb is.) IIRC from buying parts, there is some variation on this depending on engine and type of truck. I've replaced both rear sensors several times in 7 years, but the front (sensor 1) only on bank 1(driver's side).

Click to expand...

So long as I get the pre-cat sensor on the opposite bank from the one that supplies signal to the LPG ECU it'l be fine. I just have to find which bank the LPG ECU is connected to....

PlayingWithTBI said:

You should probably use a WBO2 sensor, something like this (0-5VDC) It'll give you a lot better range and feedback.
https://www.amazon.com/s?k=Innovate+3877&ref=nb_sb_noss_2

Click to expand...

I think the gauge (it's a £10 ($13) thing - no more!) is configured for a 0-1VDC signal. All I'm really looking for is which direction the AFR goes during transients - and for oscillations/overshoots. There's provision for going big rich at a particular TPS. Both of those are adjustable and I want to see where they are in relation to kickdown downshifts. There's a few other things I should be able to read from it that will help fine tune the system (eg, over-run fuel cut off, default stepper position, etc).