Before you guys chew me out I have done the searches and can not find a clear answer.
I have an 98 GMC SCLB that I swapped a 305/4L60E out and installed a 350/4L80E and it keeps setting a PO160 which is the post cat O2.
While viewing the live data under any condition Idle, acell, brake, etc the O2B1S2 (V) would read a steady 0.445 or 0.450 so I replaced the O2 sensor but it still reads the same.
Does this mean the cat is bad or on it's way out?

Thanks AJ

 

post cat 02 doesnt matter... get a tune to get rid of it

Precat 02 is what matters.

 

Is that what it means? that the cat is bad?

 

P0160 "O2S Circuit Insufficient Activity Bank 2 Sensor 2"

I believe the Sensor is dead?

 

I just put a new one in.
Do you know what the output of the 4 wires should be coming from the harness? (with a multi meter)

 

You'll need a schematic, but 2 of the wires are for the heater, one is the signal wire, and one is the ground. An O2 sensor will actually produce it's own voltage...if you were to unplug it and test the signal wire, you would see about 450 millivolts (on average, it shold fluctuate slowly with not as many cross-counts as a front sensor), with the engine running and the sensor properly heated up. The rear O2 sensor should not fluctuate as rapidly as a front O2 sensor if the cat converter is doing it's job. If the rear O2 sensor is fluctuating rapidly, the cat has lost it's ability to perform properly. If the cat were starting to clog you may see a more steady voltage like you reported.

Considering that there has been an engine and trans swap involved, I'd first check the wiring and also make sure that the tune is compatable with the electronics of the 4L80E transmission, I know that segment of the swap in the PCM can be tricky, from what I've read. Double check the harness, make sure that no wires are pinched and that there aren't any pins bent over in any connectors.

 

The PCM and wire harness came out of the pickup that the engine and tranny came from. I have went over the wires many times and it does not appear that any are damaged.

 

i dont know how easy it is to replace the Cat on your truck. but it wouldnt hurt.

 

You could actually unplug the sensor and probe the sensor wires, one of them should show a slowly fluctuating voltage, between .1 and .9 volts. If you find the wire that's producing a voltage and it's stuck at .450, either you have a bum sensor or something else giving it a false reading. If it has vent holes, make sure that they are not obstructed, also make sure that there isn't any foreign matter on the probe. If it is fluctuating as I mentioned but the scanner is still showing a steady .450 volts (with the sensor plugged in of course), then there is either a problem in the wiring, the pin fitment at the PCM, or the PCM itself. If it's fluctuating rapidly the cat converter has broken down and is no longer oxygenating the exhaust, but this reading would contradict what you're seeing with the scan tool, and would mean that you actually have 2 problems (not likely but possible). Of course check for exhaust leaks around the sensor and obvious stuff like that, although an exhaust leak should not show a neutral voltage reading and rather a low voltage reading since the sensor will be exposed to more oxygen.

 

Just get a Nelson tune and turn the rear O2's off and your good to go