I'm about to replace both of mine. A brief note my truck's cat is on vacation until I can get a replacement and my truck has still failed to produce a CEL for it so I'm fairly certain that my rear O2 is dead. I checked today and noticed that according to Torque pro my front and rear O2 sensors both bounch between 0 and 1v. So I have a feeling one of them is shorting and causing hell.

Edit: Apparently this is normal....

 

Your sensors are reading correct. They may be old and lazy, but, they are still sorta working.

 

I think I actually found the answer I was not looking for but needed on another site that explained how O2 sensors work. So I've often had a surging with my truck. Up until recently it's mostly been felt while driving. Here lately you can feel it while my truck is idling in both neutral and drive. Well apparently these things can do what's called an O2 Hunt which can cause surging.

I don't have a picture of the actual surging or the high spikes but sometimes the O2 would spoke to 1.2v while idling and the rpm would drop quite a bit. I do have this picture where you can see the O2 readings effecting the engine RPM though.



At the very beginning of that chart you can see it effecting the RPM.. then after that it just stops. This is how the truck performance happens too. One minute it runs super smooth, the next it idles rough and luggs. That reading on the back O2 concerns me though so I will replace both just to be safe. The front one is entirely my fault. I ordered an O2 sensor off Amazon which they claimed worked with my truck but it turns out the pigtail was too short. So I extended it which could have worked but I got lazy and used butt connectors instead of soldering it. My intent was to buy the correct one but that job was so crappy that I never really got paid anything more than what it took to live. Now I've got a damn good job I'm getting all of this sorted out. Lol

 

You want NTK, or Denso O2 sensors. Skip the bosch fellers, our trucks don't like 'em.

 

I ordered a Denso 234-4077 Oxygen Sensor that supposedly fits my truck but the pig tail is way too short. I'm going NGK this time.

 

Double post for update purposes.

So this morning I found the offender. I fired up the truck and got A CEL for P0138 O2 Sensor Circuit High Voltage (Bank 1 Sensor 2). Also one for Cylinder 5 misfire and cylinder 7 misfire which are still pending.

So I checked my graphs again and the downstream O2 sensor is pegged at 1v. Now the funny thing is I unplugged it for a few seconds when leaving work and drove around the building to see if that made a difference. My truck didn't notice it was unplugged. So that's what I thought the CEL was actually for until I saw the graphs. Nope... It's legit dead, which leads me to think it's been dead for a while and the system didn't think it was. It's the original O2 sensor so I'm not surprised. Lol

 

Rear O2 sensor is just to monitor the cat. So long as the PCM sees a reading that it thinks is 'within reason', it will assume the sensor is ok. They gotta be really screwed up before they will actually set a code.....

 

Shoot I thought I uploaded that picture too.



So the odd thing is since it threw this code my truck has actually been going into 1st gear like it should and my truck suddenly found it's.... Fortitude again. Lol

I'm fairly certain they're both bad. I read somewhere that the rear shares the same circuit as the Governor pressure sebsor., Then again I've also read the same about the front sensor.

 

Yeah, lots of stuff on the same 5 volt buss, and one of them going belly up can cause all sorts of interesting problems.

Misfires on 5 and 7 would make me suspect the plenum gasket.......

 

Yeah, I'm keeping an eye on that one. I've already done the Hughes plenum plate repair 3 heard ago. I looked the other day and didn't see any oil in there.