o2 Sensor Not Switching

$EE Impala SS PCM/Drivetrain in my 63 c10.

Scanner shows the o2 sensors stuck at 453mv. They never switch. Verified good AC Delco o2's by sticking them in my other LT1 car. Verified heater circuits by comparing sensor body temps between the 2 vehicles both well above 100* after a minute or 2 of key on / engine off. Verified continuity of PCM pins between o2 connectors and Clear Pins 7&8, 19&20 all measured 0.3>0.6 ohms. I've also tried my spare PCM. I'm using tuner pro to edit the files and eehack to flash and log.

I know its running pig rich, I can also command a really lean AFR and it seems to lean out and die based on smell (I don't have wide band.), with no change in the o2 numbers.

Short of replacing the entire wiring harness, I have run out of things to check and or try. Anybody here have any experience with this or thoughts?

Help me please.

-Brian

453mv is pretty much reference voltage, your o2 is effectively unplugged.. mispinned, broken wire, no ground, etc. a connected and functioning o2 would never read a constant voltage near switch point like that.

Where did the harness come from? Did you do harness mods or have a custom harness made or what?

I'd suggest maybe the wires are wrong at the O2 plugs but the heaters would not work if they weren't connected correctly. Still, the O2's should have 3 different wire colors. The 2 wires that match will be the heater. The remaining lighter color wire is the sensor positive and the remaining darker colored wire is the sensor negative. Check that the sensor positive goes to pin 7/19.

You could also try measuring the sensor with a voltmeter and see if you get anything there.

Per my FSM, I've got 7&8 as one side and 19/20 as the other. I've checked continuity on these pins. I will recheck that I've got the high/low's in the right sockets.

I'm beginning to suspect that I may have just crappy enough wire that the heaters can't pull enough current to stay hot enough. I've ordered up new o2 connectors and PCM pins and hopefully next weekend I can put all new wires on the o2 circuits with a dedicated fuse for them and see what happens. Cheap Summit brand long tubes with the o2 sensors about 6" back from the flange on the 3" dual exhaust. Which I regret but haven't felt like replacing with 2.5" or even 2" for this bone stock LT1. I think they just can't get/stay warm.

The harness is a pretty pieced together B-body harness that I maid myself. It worked for 4 years but the 22year old wires might be starting to go. I'm just hoping I can limp it along until I'm ready to build a whole new harness with all the extra stuff I have that they never include with those stand alones.

Thanks for the suggestions guys and I'll post back later with this weekends results.

-Brian

Weekend Update:

New dedicated heater circuit with all new wires. Left side o2 sensor works again.

All new wires from PCM to Right Side o2 sensor including all new connector pins. Still no RH sensor reading.

Swaped PCM pins right to left; problem follows RH sensor location.

Swap PCM pins back to correct positions.

Swap sensors left to right; problem does not follow sensor.

The problem is in the right handwriting, however the right hand wiring is all brand new including pins. Is it just not heating up? Is there a certain resistance value I should expect on the wires?

-Brian

I got it wrong before. The darker color wire is the O2 sensor signal and the lighter color wire is the O2 sensor ground.

Resurrecting the Dead.

2 years ago I gave up on my shitty harness and just programmed it to run in Open Loop. Since then I have installed a harness from Current Performance. (I liked their fuse/relay block architecture the best.)

However I am still having this issue. I have the o2 Sensor just hanging out in free air at the moment so I can hit it with my plumbers torch. When viewed in $EEHack, the o2 millivolts never move from the 450-453 range with Key On Engine Off. Does it need to actually be running? When I put my DVM on pins C19/C20 at the PCM and warm the o2 with the torch I can see between 0.1 and 0.9v at the pins on the PCM connector. So it isn't wiring and it isn't the o2 sensor. I also tried a spare PCM with the same result.


-Brian

Finally got it to throw me out a couple of codes. 13 and 63. I'll run through the checks in my FSM but I am about 95% certain that the issue is now that I cannot keep the o2 sensors hot enough for them to actually produce a voltage long enough for the PCM to see it.

-Brian

no it doesn't have to be running. again, you probably have an open circuit. your o2 and your ecm are not connected. there is no way a real o2 sensor would read anything but HIGH or LOW in a non-running engine state. what does it read with the o2 disconnected? how about ground the o2 wire, it should swing to zero.