I have read as many threads as I can, here is my scenario.

Was playing around with the transfer case and unplugged all the wires including the RH Downstream O2 sensor. Car was fine since I got it before this.

After putting it all back together, car started throwing Bank 2 Sensor 2 Lamba, and occasionally DS o2 heater code.

Fiddled around a bit and with 92,000 miles figured the O2 sensor must have buggered up somehow. Bought a new one, screwed up getting it out, so took it to my local shop and they cut the new one in, cause even they couldn;t get it out. OK lesson learned there.

Drive it around, SES comes on again. Using the tool I have I get the same codes. OK so now some serious debugging.

The voltage on Bank 2 sensor 2 always sits at .452V as expected at the cold start. Once the system heats up, the .452 gets up to about .485 but does not fluctuate. Then the system throws the code.

So, all the other sensors are jumping up and down as expected.

I got my multimeter out (oh no?) and started checking.

The power to the heater circuit at the plug from the Fuse Box has continuity and is providing 13.7 or so when on. The voltage coming from the sensor is fluctuating as well. I even crossed over the working LH circuit to the RH sensor and it worked fine.

Switching the other way, the LH did not register as the RH.

So the issue is downstream of the sensor voltage to the ECU right?

Pulled the ECU connectors (battery disconnected) checked continuity on all three wires to the ECU and success.

Then checked the Ground wires out of the ECU to the body and they checked out.

SO, if I haven't confused you, why would this one circuit be not functioning when everything else in the ECU including the other three sensors, and all the other vehicle functions are working perfectly apparently?

I did read about shielding but I stripped back what I could reach and found no issues.

Bad ECU? I am out of ideas....

Any help would be appreciated.

 

Did you check that none of the pins in the connector push up into the housing?

 

Thanks for the fast response, best I can tell all the connections appear to be fine.

On the sensor connector, I stripped back the downstream wires a little to check continuity through the connector, reminds me I can check those bare wires sections when running to see if the voltage is getting through.

I did electrical tape these up in case you were wondering, lol.

Very frustrating.

 

Update,

With the heater circuit on, the LH DS measuring 700mV or so, I can measure the voltage on the RH DS and get 700mV but diagnostic still show 700mV and 483mV respectively.

Aargh, its like the logic doesn't recognise the heater circuit so its not changing to the O2 voltage. The DS heater circuit is only one circuit right? so the flag to the ECU would be the same?

 

So here is the solution.

I came to the conclusion that it was the ground inside the ECU, probably not a good sign.

Having measured everything else to be working, I spliced into the Red Black wire on the harness side about 2 inches from the connector. Added a ground up to the under the console (I am wiring in the CDL switches anyway).

Once grounded the ECU recognised the B2S2 O2 Sensor Voltages. Remove the ground and it goes back to around the usual .452 or thereabouts. You have to wait till the system really heats up and once the heater circuit turns on, you see the voltage readings change.

In essence, I spent in the end around $200.00 in parts in labour for a ground short and a piece of wire lol.

Anyway, thanks for all the help, there were snippets around of being an ECU ground issue and without those hints I would have struggle to solve this.

I learned a lot about O2 Sensors on this problem so I am smarter for it!!

Cheers!

 

So I have a similar issue but my downstream sensor goes to 0 after the warm up phase. If I understand what you are saying, you grounded the specific S2 sensor to the chassis at the plug just before the ECU? Any pics as to what you did would be great if you have them. Thanks

 

Hey,

I would caution on this, I do not know the specifics of your issue but I kinda exhausted my testing before butting anything. I can hook up a multi meter to the hot O2 Sensor and see the voltages, I never got a 0V. I checked multiple times on the wiring to and from the sensor and even swapped out the sides connection to verify (the ECU doesn't care what sensor its attached to).

Specifically, my ECU would read 452mV when cold and about 480mV when hot. Not sure why it move, probably a small change in resistance somewhere due to heat?

When I connect the ground the ECU reads the voltages, usually around 700mV when hot and cycles up and down a bit, mimicing the other downstream sensor. Remove the ground and back it goes to nominal 450mV or so.

Here is a pic of where I spliced it on Bank 2. Bear in mind that I am in the middle of a CDL install so my console is wide open and makes things very easy to access this harness.

Cheers,

 

No worries I just was curious as I have been reading the posts on my issue and have went through the whole bad sensor, switch the sensors routine already and have determined there has to be a ground missing along the line but since it is a down stream I have not been in a hurry to do much more. Thanks for the info, It is helpful in my research.