V8 swap O2 sensor wire question

V8 swap O2 sensor wire question

Postby Bigforkg [OP] » February 14th 2021, 12:20am

So Im at the o2 sensor point and unsure of the wiring of them. My print out for the VCM list the wires as HO2S B1S1 has a "HIGH" and "LOW" wire. Also HO2S B2S1 "HIGH" and "LOW" wire. I get the heated wire part but everything I see about o2 sensors show a signal wire and a ground wire. The Schematic is for a 99 5.0/5.7. What of those 2 wire go together?

MY swap is a 98 Astro and the donor is a 5.7 out of a 99 Tahoe. Im using the Tahoe VCM and using the o2 sensors for a 99 tahoe. The plugs are different
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Re: V8 swap O2 sensor wire question

Postby Big_kid » February 14th 2021, 1:18am

Get the plugs for the 99 Tahoe and solder them in place, adding wire as needed to replicate the circuits exactly as they were in the Tahoe. They're on different pins, if you tie them together I would expect you to have O2 sensor errors.

I ran into similar differences on my 95 swap, I've still not added a heated sensor. It runs ok, I just don't get closed loop.
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Re: V8 swap O2 sensor wire question

Postby Bigforkg [OP] » February 14th 2021, 4:22pm

So after 3 more hr of searching I believe "low" is ground and "hi" is signal. Now I found the Astro o2 is isolated ground and the Tahoe o2 is case grounded.

New question is will a case ground o2 work with a isolated ground? Wouldn't a ground be a ground?
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Re: V8 swap O2 sensor wire question

Postby sfeaver » February 14th 2021, 5:11pm

Low is "ground" for the signal only. You can repin the harness side, or repin the 02 sensor. The astro sensors wont work anymore. I used 2002 Express sensors and changed the connectors. If you already have Tahoe ones, they will work too. You might also have to get that Bank 1 sensor 3 programmed out or you will have a check engine light.
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Re: V8 swap O2 sensor wire question

Postby AstroWill » February 14th 2021, 5:22pm

4 wires for each heated o2 sensor, 2 are for the sensor and 2 are for the heater, two wires going to the PCM/VCM will be the same, heck even the heating circuit should be the same.

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Re: V8 swap O2 sensor wire question

Postby Bigforkg [OP] » February 15th 2021, 3:37am

sfeaver wrote:Low is "ground" for the signal only. You can repin the harness side, or repin the 02 sensor. The astro sensors wont work anymore. I used 2002 Express sensors and changed the connectors. If you already have Tahoe ones, they will work too. You might also have to get that Bank 1 sensor 3 programmed out or you will have a check engine light.


Im repining the o2 to match the astro plug. Just want to 2x make sure they are wired correct. The reason is in trying to find answers I found at LT1swaps that GM used a "isolated ground" and a "case ground". I also read and can't find it now that 1 of the vmc won't work with the opposite o2 sensor because of the ground. Do you know what yours is? 3 is taken care of.
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Re: V8 swap O2 sensor wire question

Postby sfeaver » February 17th 2021, 4:03am

I used the 0411 PCM, I think the Astro got that starting in 99 or 2000. From what I understand, the case ground sensors have the four pins in a row on the connector. Isolated is the four pins in a square. Are you using the blackbox pcm?
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Re: V8 swap O2 sensor wire question

Postby Bigforkg [OP] » February 18th 2021, 2:20pm

sfeaver wrote:I used the 0411 PCM, I think the Astro got that starting in 99 or 2000. From what I understand, the case ground sensors have the four pins in a row on the connector. Isolated is the four pins in a square. Are you using the blackbox pcm?


Im using the Tahoe black box, the Tahoe used the 4 wire flat o2 plug and the Astro has the 4 wire square. I just thought the Tahoe had square plug o2 as sensor 2 in both banks. Do you know any difference in o2 the way they work or read between v6 o2 or v8. Or in other words would a v6 o2 work in a v8?

Astros in 2000 still use the black box vcm.
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Re: V8 swap O2 sensor wire question

Postby sfeaver » February 20th 2021, 5:40pm

Looks like the V6 Astro sensors are different from the V8 ones. Not sure why, but different part numbers. Now I have to go check what I did with my post cat sensor, I dont think I changed it. Your right about the square plug as sensor 2 on both banks. Not sure why they arent all the same, I would guess the PCM wasnt capable of all four being case-isolated.
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Re: V8 swap O2 sensor wire question

Postby Bigforkg [OP] » February 21st 2021, 5:39pm

sfeaver wrote:Looks like the V6 Astro sensors are different from the V8 ones. Not sure why, but different part numbers. Now I have to go check what I did with my post cat sensor, I dont think I changed it. Your right about the square plug as sensor 2 on both banks. Not sure why they arent all the same, I would guess the PCM wasnt capable of all four being case-isolated.


I was wondering if the part # are different based on plug and wire length? I dont know. I have to dig out from under the snow my 99 and check those.
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Re: V8 swap O2 sensor wire question

Postby Bigforkg [OP] » March 28th 2021, 10:38pm

I think the answer is the flat plug (case grounded) O2 will work. I say this because I dont have any codes, Air/fuel is 14.1-1. But it sells rich in the garage with the door open.
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