No O2 sensor reading... ???

[FSJ Guy]

I am running a 16197427 PCM on an AMC 360 V8 engine. This is my 3rd TBI conversion, second '7427 conversion but it's been several years. I am running a modified $0D code. All the other sensors read correctly, so I feel that I have the correct XDF and acquisition files in TunerPro.

I am running a Bosch 4 wire O2 sensor. I have double checked the heater wiring as well as the sensor wiring. They appear correct. The heater circuit on the sensor measures about 5 ohms and when I probe the O2 sensor with the engine running, I get aprox 0.100 volts, I think the sensor is good. It better be. I purchased a new one.

But when everything is hooked up, wit the engine running, TunerPro shows aprox 0.440 volts. and it NEVER moves.

That tells me it is not reading the sensor. The other thing that tells me the sensor is not being read is that ALL my BLM #s are 128. And I KNOW that is wrong.

Any idea on where to start?? I swapped PCMs and there was no change. The swapped PCM read a constant 0.453 volts, similar to the original one I was using.

[shimniok]

I'd lean toward a suspect definition file, I guess. Any hacks applied? Or not applied that need to be?

That's assuming the voltage at the PCM side of the O2 wire is reading the correct voltage -- might be worth verifying.

What voltage does the O2 wire read when disconnected from the sensor?

[babywag]

You have a wiring problem, circuit is open.
.45v is default value

Verify you have 12v key on to heater wire, and heater ground.
Verify signal wire from o2 to pcm, and signal ground to pcm.

[babywag]

Also verify the wires are pinned correctly @ pcm

[FSJ Guy]

Problem solved:

I mistakenly wired the Sensor Ground back to the PCM instead of to an actual GROUND. This was discovered by metering the two grounds. The potential should have been zero, but instead was ~2 volts. I checked the schematics and realized my mistake.

Once I grounded that wire (leaving it connected to the PCM), the O2 sensor started reporting and all is well.

Thanks for the pointers and help!