Ferocity02

iTrader: (60)

I just put my truck back to stock other than a 4L80E instead of the 4L60E. I put in brand new Bosch rear O2 sensors. I'm getting codes P0140 and P0160 for no activity for the rear O2 sensors. When I log with EFILive, these sensors are flatlined at ~450 mV +/- 5 mV... no real activity whatsoever. It's basically like the sensors are unplugged.... I unplugged a front sensor and it also shows ~450 mV.

I bought another O2 sensor, same thing. The heaters in the sensors work great. I bench tested one sensor and I think it's working fine, responds to fresh air vs. gasoline-rich air.

I did continuity tests on the tan and purple signal wires that go to the PCM and they are fine and do not appear to be shorted to any other wires going to the PCM or ground. The wires are physically in tact, no melting or anything of that sort.

I am using a stock tune flashed into the PCM with nothing but a 4L80E trans segment that has been modified slightly for gearing. The engine calibrations are all stock other than a handful of transmission related DTC enablers that were changed. The DTC enablers for the rear O2 sensors are all stock... "2 trips, emissions related."

Anyone have any ideas? I am at a total loss here.

Pacer Racer

iTrader: (6)

Are you sure that they are the right type of sensors. I know there are 2 differant types. One is internally grounded and the other requires one of the harness lead for the sensor to be grounded.

Ferocity02

iTrader: (60)

I mean they are the right size and connector. They are Bosch 13474. I bought the first two on eBay after searching for which ones I needed. And then I went to Autozone and they also recommended Bosch 13474.

Ferocity02

iTrader: (60)

Anyone have any thoughts? Still scratching my head on this one. I flashed in a 100% stock tune and no change.

Pacer Racer

iTrader: (6)

Take your ohm meter and remove C1 from the PCM and the O2 plugs, then check to see if pins 25, 26, 28, 29, and 63 are common to each othet, if not you require ground case O2 sensors

Ferocity02

iTrader: (60)

What is C1?

How do you know what kind of sensor it is? I can't imagine the recommended sensor for my truck online and at Autozone is not correct.

Pacer Racer

iTrader: (6)

C1 is the blue connector on the PCM
You also want to unplug the O2 sensors from the harness. If the application takes 2 differant types and they didn't ask if you needed grounded case O2 sensore or ungrounded ones how can they be sure they're giving you the right part?

Pacer Racer

iTrader: (6)

Every web site I looked on, NAPA, Advance Auto, AutoZone all offered 2 differant downstream O2 sensors for your truck. If the parys guy didn't ask the first digit of your VIN they should go back to flipping fries at some greasey spoon. If the first digit of your VIN is 1, 4, or 5 you have the correct O2's, if it isn't then you have the wrong ones

Ferocity02

iTrader: (60)

Welp... I figured it out. Turns out the 2 sensors I got on eBay were bad. When I bought the 3rd sensor at Autozone and tested it, I neglected to ground the sensors case to the exhaust. It works fine once the case is grounded. The sensors I got online are the same as the one I got locally, albeit without the boxes and half the price. Maybe they were fakes.

Hopefully I can return the O2 sensors even though I installed them. If not, I'm going to file a complaint with PayPal.

Pacer Racer

iTrader: (6)

you should be able to just ground the harness leads and not worry if the O2's are grounded or not.
Some people say it will cause a grpund loop but Ive never had an issue doing it.