PCM Output Voltages - O2 Sensor Issue Diagnosis

[evilstuie]

Hey guys,

I've been chasing some answers to this on a few forums but no-one seems to know.

I'm chasing some electrical gremlins in my 0411PCM LS1 swap into an 85 TransAM and need some help with what I should be seeing on the O2 Sensor wiring.
These are using the flat black 4 pin O2s for Bank1 & 2 pre cat, no second sensors, and I have a wideband for tuning on left exhaust only.
When I log in HP tuners when the car fires up, my left o2 is sitting around 0.1v-0.3v and the Wideband is completely lean (20.0), the right side is sitting on 0.448v with a bit of a twitch but doesn't move. ( suspecting it could be dead)

Here's the thing though, the right side is nice and hot at the exhaust side, but the left side I can grab onto after a minute of the car running and it's only slightly warm, like it's not even firing.
I checked all the coil wiring and injectors for correct voltages, 12v where it should, ground on the coil pack, and about 430ohms on the control wires.

I got down to the O2 sensors and got these readings:

Left side:
Pin A: 4.4v
Pin B: 1.26v
Pin C: GND
Pin D: 12.4v

Right Side:
Pin A: 4.4v
Pin B: 1.26v
Pin C: 12.4v
Pin D: GND

I was told the heater pins C&D don't matter with polarity, but as far as I know Pin A is meant to be low reference so I was expecting something of a 0v / GND continuity situation and Pin B is High which I expected would be 1.0v.

Is anyone able to confirm what voltage should be outputted from the harness when the O2 sensor is unplugged?

Also, I find it strange with all the DIY work done on these and custom harnesses that no-one has ever put together a table with the PCM pinout that includes the expected voltage outputs, inputs and resistances so you can do a complete check of your harness and PCM prior to firing up...
I'm putting one together as I test everything, but it seems pointless while I'm still having issues, as I won't know what's correct and what is giving bogus readings due to wiring issues/ stuffed PCM.

Any help as always is appreciated.

[Cincinnatus]

O2 voltage on scan data should .450v not running or unplugged. Running, once they heat in 30s or less, they should start switching high and low. If they don't switch, your short term fuel trims will add or subtract fuel until switching occurs or until trims max out. You can reset trims with scan tool or removing battery power from PCM. If you can get .450v unplugged but not plugged in, check wiring as some years o2 will plug in but wires are wrong, or replace O2 with known good.

[evilstuie]

O2 voltage on scan data should .450v not running or unplugged. Running, once they heat in 30s or less, they should start switching high and low. If they don't switch, your short term fuel trims will add or subtract fuel until switching occurs or until trims max out. You can reset trims with scan tool or removing battery power from PCM. If you can get .450v unplugged but not plugged in, check wiring as some years o2 will plug in but wires are wrong, or replace O2 with known good.

Hi,
Yeah I'm wanting to also diagnose the PCM though, in case it is the problem, which could explain the left bank issue.

I'm using the correct narrowband sensors (black flat connector, ground supplied [not isolated]) and it's giving me 0.1v plugged in. I was more worried about the voltages being sent by the PCM.

[Cincinnatus]

I fear you're heading down the wrong path diagnostically. I recently installed a used sensor, same plug, got low voltage like you and discovered signal wire reversed with reference (or however they are termed). I have had new sensors not work properly. My recommendations are going to find if it's a bad O2. PCM voltages aren't the way to diagnose this problem. You can always swap PCM and see, but if you have an electric problem causing this and it damaged the PCM, you risk damaging the swap unit. Also, cheap O2 sensors are a mistake, though I've had bad new units from good manufacturers. Swap your sensors and see if the problem follows the sensor.

[Charlescrown]

You sure your getting 4.4 volts from a narow band sensor?

[evilstuie]

You sure your getting 4.4 volts from a narow band sensor?

Not from the sensor, from the PCM.

As I see it there's about 4 possibilities here:

BAD PCM - throwing out bad voltages
BAD O2 sensor - sensor has gone from working 6 months, stored in dry place and reinstalled to fail.
Leaking voltage - sensor uses the grounding of the exhaust to operate and this is being interfered with by a short somewhere causing the ground not to work.
Bad wiring - incorrect pins or wiring

I'm trying to confirm what voltages the PCM would be outputting for the HO2S High and HO2S low signal values (if any) to confirm the PCM is doing what it should.
This is tested at the plug end of the harness with the O2 sensor unplugged

If the 4.4v and 1.26 volt readings are supposed to be there, then I can look further down the line, but the first step is to check from the PCM, as I don't have a spare to check with at the moment. (In Australia and someone bought up all the 0411PCMs so they can sell them for $400 a pop)
Currently no-one can tell me how the PCM low and high signals function from a voltage signal perspective, so the values I have mean nothing without a reference.

The O2 sensor I can test with a butane torch and a multimeter, which I'll do at some point or switch out.

I'm more focused on the PCM side of things because while getting the narrow band o2 sensors working is useful, the whole left side of the motor not firing is more critical for me at the moment, and if it's a faulty PCM at the cause of it, then I can feel a bit better shelling out $400 for another one.

The o2 sensor dying in storage at the same time as a wideband dying is highly unlikely, and I've checked the wideband with a few drops of petrol to confirm it changes the readings on the output 5v as well as the gauge.

Lastly the bad wiring, the whole harness is a direct swap from the donor LS1 vehicle. The old 400 motor was running a 24x conversion made from a VY commodore and had all of the electronics (BCM and dash included) installed and working prior to the start of the project.
None of the PCM harness pins have been altered except for slipping a wire in the EGR pin for wideband monitoring through HPTuners and the reference ground.

[Cincinnatus]

Unplug the sensor and PCM will run open loop and fueling will be PCM controlled but no feedback from faulty sensor so no fuel trim adjustment. Wideband should read accordingly.The wideband likely isn't dead, it's reading what the PCM is doing from the narrowband that may be causing your problem. Lastly, PCM operating system dictates pin function, don't assume, verify with a pinout. I've had O2 sensors lie, so your butane torch and multimeter test may give some results, but I wouldn't assume that means that sensor works properly. Also, a dead hole from a bad or leaking or weak injector will cause lots of problems with fueling because O2 will see O2 from unburned cylinder, add more fuel for that bank and make everything worse. This problem should be a bit more obvious typically.

[evilstuie]

Unplug the sensor and PCM will run open loop and fueling will be PCM controlled but no feedback from faulty sensor so no fuel trim adjustment. Wideband should read accordingly.The wideband likely isn't dead, it's reading what the PCM is doing from the narrowband that may be causing your problem. Lastly, PCM operating system dictates pin function, don't assume, verify with a pinout. I've had O2 sensors lie, so your butane torch and multimeter test may give some results, but I wouldn't assume that means that sensor works properly. Also, a dead hole from a bad or leaking or weak injector will cause lots of problems with fueling because O2 will see O2 from unburned cylinder, add more fuel for that bank and make everything worse. This problem should be a bit more obvious typically.

Yep but in that scenario with more and more fuel being added the wideband would run richer.

The other issue is that the car will be in open loop even at startup and won't be changing the fuelling from o2 sensors right away.
The headers on the right side are hot right from the get go but the left bank is staying cool.

I have spark, I have fuel pressure, I have steady prime pressure, so no leaky injectors.
I don't have a noid light to test the left bank injectors, but the wiring is correct.

So if it's not firing the PCM has to be the cause. This is mainly why I want to find the o2 voltages, because the 4.4 and 1.26v seems strange and no-one can explain those numbers to me, or even confirm if they are correct. They usually misunderstand and start talking about 1v or the 0.450v. a dead o2 sensor will cause fuelling issues but it won't cause an entire bank to stop firing entirely.

If non-one knows the o2 sensor voltages, is one of the grounds on the pcm specifically responsible for the left bank injector(1,3,5,7) as in it uses this to ground these for the injectors to fire?
So far its Blue: 1,40
Red: 1,40

[Phoenix]

Unplug the sensor and PCM will run open loop and fueling will be PCM controlled but no feedback from faulty sensor so no fuel trim adjustment. Wideband should read accordingly.The wideband likely isn't dead, it's reading what the PCM is doing from the narrowband that may be causing your problem. Lastly, PCM operating system dictates pin function, don't assume, verify with a pinout. I've had O2 sensors lie, so your butane torch and multimeter test may give some results, but I wouldn't assume that means that sensor works properly. Also, a dead hole from a bad or leaking or weak injector will cause lots of problems with fueling because O2 will see O2 from unburned cylinder, add more fuel for that bank and make everything worse. This problem should be a bit more obvious typically.

Yep but in that scenario with more and more fuel being added the wideband would run richer.

The other issue is that the car will be in open loop even at startup and won't be changing the fuelling from o2 sensors right away.
The headers on the right side are hot right from the get go but the left bank is staying cool.

I have spark, I have fuel pressure, I have steady prime pressure, so no leaky injectors.
I don't have a noid light to test the left bank injectors, but the wiring is correct.

So if it's not firing the PCM has to be the cause. This is mainly why I want to find the o2 voltages, because the 4.4 and 1.26v seems strange and no-one can explain those numbers to me, or even confirm if they are correct. They usually misunderstand and start talking about 1v or the 0.450v. a dead o2 sensor will cause fuelling issues but it won't cause an entire bank to stop firing entirely.

If non-one knows the o2 sensor voltages, is one of the grounds on the pcm specifically responsible for the left bank injector(1,3,5,7) as in it uses this to ground these for the injectors to fire?
So far its Blue: 1,40
Red: 1,40

I'm sure that you have already done this, but at least in factory form each bank of fuel injectors is connected to a fuse. Could one of them be blown?

[Phoenix]

Also, what engine codes are you getting?