Caravan O2 sensor Madness

Hello, this is my first post. Thanks in advance to anyone who takes the time to read it & offer suggestions.

This is after seeing Scanner Danner's WARNING on aftermarket O2's for chryslers videos.....
2005 Grand Caravan 3.8L family van. Bought with 99k, now it has 185k, never touched the O2's, has always ran great & gotten 18mpg town, 25 freeway.

All of the sudden, set codes for upstream O2 slow response, and catalyst efficiency.
Get this... The factory sensor is a Bosch! (# 56029085AA) That's what I pulled out, and when I unwrapped one that the local Dodge dealer handed me, it was identical. Checked voltages at the harness to the sensor (sensor unplugged), here they are with engine running:
Heater+ 9.5v
Heater- Grounded, 4 ohms
Signal+ 1.7v
Signal- 2.5v

I don't have a spendy scanner, so am using a bluetooth adapter and a tablet to look at live data. When I ground the signal+ wire while looking at live data, the reading goes right to 0v. Here is what the sensor data looks like after I have driven the van around and everything is fully warm:

-Steady 2000rpm / upstream switches past 450mv, but not with proper amplitude or frequency. Maybe one switch every 2-3 seconds, and seems biased rich, sometimes barely goes lower than 400mv. Definitely looks lethargic compared to my 97 silverado. The downstream holds steady at 700mv. Fuel trims nominal to slightly positive.

-Idle / Immediately upstream stops switching & holds steady at 700mv, downstream matches. Fuel trims go negative to -6% and hold there. On throttle snap from idle, both sensors snap to 200mv, then settle back at 700mv.

I have tried a new Bosch, and a new Denso sensor with same results. I bought an NTK, but when I unboxed it, it was identical to the Denso even though all the packaging was correct (NTK# 23566). Didn't bother installing it. I've also disconnected the battery between trials to no avail.

I don't know what to do next, tags are expired as I cannot pass state emissions.
Any suggestions?

both sensors snap to 200mv, then settle back at 700mv.

This is suggesting an actual rich condition, though I would like to see all 4 O2 sensor voltage readings with it plugged in and backprobing instead of unplugged.
If you hold it at 2500 for a few minutes, does it eventually start switching normally?
What is the history? This just started all of a sudden?
Last question for now. Are you saying the Denso O2 has NTK numbers on it? Or it physically looks the same?

Thanks for the response, I will backprobe and hold at 2500 and post the results.
There are actually only 2 sensors and 1 cat on this van. They daisy chained the exhaust manifolds together before the upstream O2.
Not much history, although it did have an EGR code before this, I cleaned the valve (all electric type) and that code disappeared. I have had to do this several times over the years, but it has never caused any other issues in the past. I have tried running it with the EGR valve unplugged and the O2/catalyst codes still return.
As for the sensor question, I mean I purchased an NTK sensor, the box had the NTK#, the clear bag inside had the NTK#, however the sensor itself looked identical to a Denso, and had the same # on it as a Denso. See images......

Every time I've run across an O2 Slow Response code on a Chrysler product, it's been due to an exhaust leak, usually from cracked manifold. Any indications of a leak on your van?

Well, nothing audible. Any more definitive way to check than listening for one?

If you have one, a mechanics stethoscope can be used by removing the metal rod at the end, and just using the rubber tube to listen around gaskets/flex pipes/O2 sensors. A smoke machine would work, too.

I rigged up something very similar to this for quick leak testing without having to run the engine:

Here are back-probed readings from the upstream sensor, using both pos. and Neg. signal wires.
This is a brand new Bosch sensor, which is the correct factory sensor from Chrysler for this van.
Sorry, not the best video quality or instruments, but I think you can get the jist of it....
Engine was at full temp here...

<i-frame width="560" height="315" src="" frameborder="0" allowfullscreen>

diypro wrote: Here are back-probed readings from the upstream sensor, sing both pos. and Neg. signal wires.
This is a brand new Bosch sensor, which is the correct factory sensor from Chrysler for this van.
Sorry, not the best video quality or instruments, but I think you can get the jist of it....
Engine was at full temp here...

<i-frame width="560" height="315" src="

" frameborder="0" allowfullscreen>

What do you mean both positive and negative? Did you measure between battery negative and the o2 signal and ground? Try measuring between signal ground and signal, it looks like the o2 and battery are not in the same electric circuit.

What I mean is I probed the positive and negative signal wires. I did not connect to battery ground, when you do that you get a reading of 2.5 - 3.5 volts because of the 2.5 volt bias on the sensors negative wire. (perhaps I used the wrong terminology for the sensor ground wire?)

diypro wrote: Well, nothing audible. Any more definitive way to check than listening for one?

Seafoam or something like that causes some heavy smoke in the exhaust.

What I mean is I probed the positive and negative signal wires. I did not connect to battery ground, when you do that you get a reading of 2.5 - 3.5 volts because of the 2.5 volt bias on the sensors negative wire. (perhaps I used the wrong terminology for the sensor ground wire?)

Ok, now i understand. I was misled by your first post with volt measurement.