O2 sensors fluctuating wildly at idle - is this normal ?

[temagnus2004]

The car recently has been a little sluggish in the lower rpm range. After 4k rpm it really comes alive like it should.

Anyways, I vag it and one code comes up: B2 S1 o2 sensor intermittent

Doing live graphs, i pick all 4 o2 to see what are they doing. The graph comes up interesting to me. 2 of the 4 sensors are rocky steady at idle and the other 2 are fluctuating wildly up and down. Is this normal ?

It should be noted that I "tested" all of the o2 sensors and they come up normal with the exception of the intermittent signal error.


any thoughts ?

[Monty23]

Yes, the oscillations are normal. Its time to replace your driver side primary (front) O2 sensor (B2S1) if your wiring is in good shape...

[OHS4]

If you ever get your rears codes out you can switch those to the front bank's and use them. They take longer to die and work fine if you move them up front and rewire them. (front and back are identical sensors (minus the plug))

[temagnus2004]

Yes, the oscillations are normal. Its time to replace your driver side primary (front) O2 sensor (B2S1) if your wiring is in good shape...

So there other two sensors that are not oscillating normal as well ?

[Monty23]

I'm not sure about the rear O2 sensors as I have never logged them. The front O2 sensors are used to adjust your fueling (only during conditions in which they are deemed accurate) while your rear O2 sensors are only used as a reference to your front O2 sensors to tell if your cats are working properly for emissions... If the rears are not throwing a code, don't worry about them lol.

[OHS4]

Yeah as long as they are the same when it comes to giving it gas and or WOT you are fine. The code just means replace that sensor. When I got that same code I replaced that sensor and then a week later the other sensor's code got thrown and I replaced it.

[Monty23]

Yeah as long as they are the same when it comes to giving it gas and or WOT you are fine. The code just means replace that sensor. When I got that same code I replaced that sensor and then a week later the other sensor's code got thrown and I replaced it.

Yea, you are better off replacing both. FWIW, I remember reading the ecu can't tell which O2 sensor bank is actually having an issue....

here is the link: audi O2 sensor testing

[temagnus2004]

Yea, you are better off replacing both. FWIW, I remember reading the ecu can't tell which O2 sensor bank is actually having an issue....

here is the link: audi O2 sensor testing

cool link - thanks appreciate it - it was odd that 2 sensors were all over the place and the other o2's were barely moving. Also, the front o2 sensors were not all over the place, just one of the them. One front and one rear sensor are oscillating and the other front and rear are rock steady

[NOTORIOUS VR]

I'm not sure about the rear O2 sensors as I have never logged them. The front O2 sensors are used to adjust your fueling (only during conditions in which they are deemed accurate) while your rear O2 sensors are only used as a reference to your front O2 sensors to tell if your cats are working properly for emissions... If the rears are not throwing a code, don't worry about them lol.

Actually the rears also have a hand in fuel trims

[julex]

cool link - thanks appreciate it - it was odd that 2 sensors were all over the place and the o2 were barely moving. Also, the front o2 sensors were not all over the place, just one of the them. One front and one rear sensor are oscillating and the other front and rear are rock steady

If it is rock steady at "0.0" (corrections) in block 001 or 002 (forget which one), it means that they are disabled due to O2 failure. The oscillating corrections mean that they are working. This is probably the same in respective block showing actual O@ voltages which should onscillate around 0.5v, which is perfect stoich AFR.

TO illustrate why, see this graph. Even a minuscule deviation from 14.7afr produces wild swing in voltage on o2 sensor: