Thread: O2 Sensor not working... P0171 new sensor still no data from O2?

Is there something else that would cause the PCM to no show data from the O2? maybe another fault or fuse or something?

Right now, my O2 sensor is not showing when scanning with either DHP or Aeroforce. my LTFT's and STFT are maxed. there has been an intermittent problem with the fuel trims climbing and i thought it was a vac leak. IAC's are good and my MAP is at about 30-35 kpa. so deff am seeing vac.

yesterday is when the problem got worse. before my trims would climb to like 10-11 but yesterday after a tune i saw it peg. i figured it was the tune so i flashed my old tune back in and it seemed fine at first. so i drove home. well during that drive the trims maxed out again. it would idle rough. that is when i went thru all the data and found that the O2 was showing 0 mv. the sensor is new prob about 2-3 months old. i removed my O2 extension and checked the wires and they all show good on my multi meter so that can be ruled out. my next action was to check the wires for the O2 in the harness. i pulled and check all the way to the passenger side strut tower. as when i was checking and looking for vac leaks yesterday i undid the harness and moved it... the wires looked all good.

what else would cause the PCM to no show data from the O2? maybe another fault or fuse or something?

I have a 1 year warranty on the sensor so I am going to swap it out anyway to be sure. I did just notice that with the o2 harness unplugged that the o2 reads 455mv. Should it read this without a sensor attached?

i think it does because it goes into like a default.

Yes...unplugged 450mv or close enough is what it shows.

By showing 0, that means it's reading a super lean or other situation. Possibly induced by a bad sensor.

could wire being shorted cause it to read 0mv? just wondering cause if it is not the sensor and nothing else would effect its values then that is all i can think to be a cause.

If you plug in a sensor and turn the car to on..but not running. You should read 450mV. Once the sensor heats up and sees exhaust gas..then it can read it.

Ok still no go.

when new sensor is in and connected, Key on only i see 0mv just like before.
when engine on, still no O2 reading.

Im next going to get a data log and see what sensors are reporting and their data. there has to be something else....

Thought i posted this last night... iphone never sent it [Ok so I pulled out the wire diagram. I know the heater circuit is good. I stripped all the tape off the harness from the PCM to the connector and it was good wih no visible damage and it was all secure. So I looked at the o2 extension again. I know I checked for continuity and resistance on each matching pair of wires. But I didn't check for a short! It is the extension all along. I have it in my lap right now. There were three wire ends that were not in the solder joint that got thru the tape and must have made contact with another wire. Time to make dinner as I haven't ate all day. Will install it later tonight or in he morning. Wish me luck that this was the only issue.

On the bright side of things, I got a new oxygen sensor now and while I have the harness apart I rerouted the wires in top of the engine for a cleaner look.]

Thank you bill for your help. knowing that it should read 450 with it unplugged helped me to eliminate other variables.

Gald...i was confused if you were w/o the harness or with etc.