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Have a 67 Chevelle with a 427 ls engine running a Gen 3 pcm. Made the harness stand alone. My o2 voltage for bank 1 and bank 2 o2s varies between 0.443 to 0.448.... I understand this means the AFR is stoic. But these values continue to bounce between 0.443 to 0.448 even when my wideband shows 18+ and the engine runs like crap.... not sure if non working o2 sensors would still fluctuate voltage.
My O2 sensors stay in a much wider range than that in my normal, closed loop operation. I'm also running a Gen 3 "P01" PCM that is either a "0411" or an "0896" using the "12208322" operating system.
To me, those numbers indicate a dead or highly comatose oxygen sensor. Do you see any power at the O2 sensor with the ignition key on? Can you tell if your OS / PCM ever enters into closed loop operation? Mine does at around 150 F for a coolant temperature - maybe 3-4 minutes in summertime outside air temperatures.
A stock O2 sensor should bounce from 100 mV or so (.1V), to 900 mV (.9V), several times a second. They're VERY narrow-band; the slightest little bit too rich, or too lean, makes them appear to slam all the way to one extreme or the other. The ECM will try to keep it right there where it goes back and forth constantly.
If your meter is REAL SLOW, then .44x is pretty believable; it's averaging out the jumping back and forth. Might want to try a different meter. OTOH if you have a wideband that shows that the mixture is really 18:1, but the ECM is thinking that it's at stoich, then you might just need new sensors. I'd try a new pair and see what happens.
there are essentially 2 circuits in an O2 sensor.. 1 is switched 12v going in for the heater circuit and grounding out
and
sensor voltage coming from the pcm to the sensor the back to the pcm.
I honestly don’t think I have 12v running to the o2s...
Looking at this (I’m only running front o2s), I have everything terminated correctly at the pcm, but I don’t remember running switched 12v to these. If that’s the case, these sensors never get hot enough to actually get any readings.. I’m guessing this is why they are stuck at .44x volts.
And now bank 1 will actually work in closed loop (when I force CL in the scanner) whereas bank 2 doesn’t seem to want to work. Which I don’t know why it wouldn’t since bank 1 works. Brand spanking new Denso o2 sensors.
by the way, this harness and original pcm was from a 6.0 Escalade...
my new pcm is from an 02 Tahoe... I know the o2 sensors differ between the two vehicles.. but they should operate the same. 12+ in for the heater that’s grounded from pin 74 on the red connector, then the ground side of the heater circuit goes to pin 80..
The newer P59 ecms used a O2 with a heater circuit, so as was mentioned, use the correct O2 for the ecm.
will do.
i rewired my o2s so they match what the pcm is from. In this case a 02 Tahoe.
it is sort of confusing that all the low reference wiring for bank 1 and bank 2 are all connected... including pin 63.. doesn’t what bank it’s a low reference to..
Circuit 413 tan wires. All tie in together..
Using the pcm to control the heater circuit before I changed to this to match the pcm (this pcm actually had 12v coming out of c2 pin 74 for the heater) bank 1 started logging fuel trims after I put a brand new o2 in.. bank 2 was still being stubborn. Also got a new o2..
I have this issue on my swap with a 2002 0411 PCM trying to use white/gray square O2 sensors. Stock, it had the triangle plugs for the front O2s like your harness. My O2 heaters are powered by ignition 12V pink wires, that has 12V with the key on, I have a ground black wire, then the purple and tan wires that both have voltage (I think one was like 4.5-5V and the other was something like 0.5V). I even tried swapping to a black square O2 that is supposed to be case ground instead of isolated ground like the white/gray squares, but same thing - both O2s show between 0.430-0.455V with the sensors plugged in or not. On mine, in the VCM Scanner it shows Bank 1 O2's as not ready, but bank 2 O2s as ready. I am only running the front O2s on my swap.
I'd recommend run the sensor that matches/was used with the PCM. That way there is no issues/concerns with parameters being off in the PCM firmware.
well, I followed your advice and I matched the wiring to my pcm.
across the board the o2 sensor leads seem to be the same pinouts.. the major difference is the Escalade 6.0 pcm provided 12v power to the heater circuit where as the same pcm in a 5.3 Tahoe go 12v from the fuse box.
so I completely re wired my o2 harness to get switched 12v from my fuse box and ground on the engine.. then left the sensor pinouts where they were.
Boom! O2 sensors are reading and the pcm goes into CL automatically. STFT and LTFTs work!
This information is awesome! It's just one more thing that people need to be aware of when messing with HP Tuners.. Imagine having a working vehicle and then going in and changing the OS/PCM just to get electric fan control, or swapping from a DBC to a DBW set up, and then losing Closed Loop as a result! I doubt many would even think about the OS/PCM requiring different O2 sensors, or that they need to be wired differently. It's another one of those "GOTCHA!" things that someone is going to get burned with.. I swapped in a Gen IV LS into my '69 GTO and had wired up the 4 pin square O2 sensors and could not get them to work. I eventually had to change the O2 sensor connectors on the harness, and go with the early Flat connectors with 4 pins in order to get everything to work. Now I know that going forward, I MUST match year of PCM/OS to the type of O2 sensors that I will be using, and that the associated pin-out must be correct as well. Thanks for sharing the information as it just connected the dots on my a previous issue that I had. Now let's hope I remember this going forward and that it saves me a bunch of time in my swap projects. Doing a Rx8 LS swap right now.. O2 sensor time is just around the corner.
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Need help diagnosing o2 issues 
