Help with O2 sensor code

[Simmo2468]

Hey,

Was hoping to get some help please with sanity checking myself. My e86 has thrown a check engine light, plugged in my reader and it is showing a 2C9F code for "oxygen sensor heater 2 after catalytic converter: activation".

I thought to have a look at the data for the sensors, to confirm it for myself, and found that bank 2 sensor 2 does seem to be static at 0.43V (no change with rpm), whilst bank 1 sensor 2 rises to 0.73V as the engine gets warm and does fluctuate slightly as it runs. So think that confirms the fault linked to the code.

The main thing I want some help with, though, is that both pre-cat sensors are showing a voltage of ~2V, which from my understanding is way high as they should be 0.2-1V typically. Is it likely that fixing the post cat sensor that has thrown the code will let these drop down?

Never had a sensor issue with this before so not familiar, but the fact it hasn't thrown a code for those seems weird. Any guidance appreciated!

(blips on the graphs below are me taking it up to 3000rpm and then releasing).

[colb]

Pre Cat sensors should be producing a regular wave form as their voltages range up and down the scale once they are warmed up and active. If you have a heater circuit fault on the sensor that part of it has probably burnt out and no longer heating it up. This will lengthen the time for the sensor to become active. Post cat sensors when viewed will look quite static unless they detect abnormality in the exhaust gas when they will show an increase in the scale on your scanner. Looks like you need two pre cat sensors at least then re scan and see how they perform before replacing the post cat sensors. Also ensure you have no vacuum leaks across the engine from split or holed air hoses, replace any you find. With your scanner take a look at fuel trims, high readings may well indicate air leaks or a bad Maf as unmetered air getting in not passed through the Maf will be picked up in the exhaust and tell the car its running lean and demand more fuel to be injected to richen the mixture. This will continue until its adding 20% more fuel before it realises its not being corrected and will set the EML on the dash to draw attention to the fault.
Only use oem sensors don't buy cheap ones, insist on Bosch as they work out of the box, expensive but you will only have to buy once.

https://www.youtube.com/watch?v=aq2IIgu1H_8

[Simmo2468]

Thanks for the info. Useful to confirm that I was right in thinking it wasn't so straightforward as I first though from the code.

I have actually just been down now to get some more info, and it has now thrown a new code at me that wasn't there earlier: "2AA9 DME: variable intake system, servo motor 2: activation".

Am I right in thinking that is the code for the small disa valve? Might explain the weird pre-cat readings if that isn't working, but not exactly easy to check.

[Simmo2468]

Update on this one.

Think I have confirmed I have a problem with my small disa and the first downstream sensor. Unplugged the small disa under the intake and it has thrown no need codes when running, and changed no values which implies that is in fact not working as intended.

Hoping to get into it without needing to take the intake off. Seems possible with other n52 cars, but haven't been able to find a video for a z4 specifically. Will update again for reference if I manage it!

[Mike6]

Hope for your sake it isnt the downstream sensor. Gaining access isnt easy as you need to get the front up high and then getting it/them out can be a nightmare as in my case. Gave up in the end and took it to my friendly garage who spent 2 hours using everything they had available getting the old ones out. The theory being that they were fitted originally without grease on the thread and had welded themselves into the downpipe. They even had to recut the thread in the downpipe to fit the new sensors.