O2S2 Voltage Always Zero
 

Hey Everyone first post on here,

I have been having problems with my 2014 BRZ A/T for a while now with rough idle, frequent stalling, running rich. Most frequent codes I am getting are P0172. I have an AEM cold air intake. For awhile I had on an aftermarket UL header, but took it off thinking the O2 sensor positions being in a different position was causing the CEL. After going back to the stock header I still had same problems with CEL and problems listed above.

After digging into my OFT deeper I found that the O2S2 Voltage always reads zero and the Wideband AFR always reads >17.0. This made me think either two things. Either I damaged the O2 sensor when changing the headers around. Or I have a loose connection between the signal wire and the ECU (I probed through the signal wire on either sides of the connection and received resistance).

Thinking it was most likely a damaged sensor I bought a Walker Downstream O2 sensor (part#: 250-24440) and just replaced it. I turned on the car for a minute thinking I would seem some response to the O2S2 Voltage but it stayed at zero. Do I need to let the car run more and log the data to see if the values change? Should I next look for a loose connection? Could it be anything else?

Thank you in advance.

Check for leaks and clean the MAF sensor. If those don't do it, probably damaged MAF or O2 sensor.

It's the aem intake, get rid of it. It's known to make the car run rich. Take off the intake go back with oem and restall the headers and you'll be good

I have done both of those with checking for leaks and cleaning the MAF sensor. The MAF is reading correctly from the data I've pulled from the OFT. I agree that is my thought too but I just replaced the O2 sensor...

Why would the Wideband AFR read lean (>17.0) if the car is actually running rich (my MPG and nose can tell its running rich) along with the O2S2 voltage reading zero always?

WBO2 is if you reuse the rear O2 input so just ignore. I put money on the fact the OFT doesn't log correctly for the rear O2. Suggest putting up your Cal ID and see if others have this issue.

Are you using the MAF box that comes with the AEM? I reckon the intake could be your problem.

Okay I will go back to stock and see if the problem is fixed. I will have to wait until september though as I won't be going back to where the CAI is located until then. Thank you everyone for the help!!!

If you're running the OFT then just re-scale the MAF on your tune. It's an easy and quick fix. Are you running the MAF box that comes with the intake?

+1
That P0172 lean code usually means the ecu is applying over 30% fuel trim correction and the afr is still not correct. Not something you wsnt to leave till September. You might have other issues than the intake , you might have damaged 02 sendor or exhaust leak

Okay I will try to do a little research tonight on rescaling the MAF. And yes I am running the AEM MAF box that comes with the intake.

The car is not running lean. I can smell exhaust fumes more strongly and my MPG is down to around 24 instead of in the 30's. Running rich should not damage the engine I would think? I will look at your MAF scaling post later tonight. I don't hear an exhaust leak, but it could be small. Just replaced the heated O2 sensor yesterday.

Running too rich will wash the oil off the cylinder walls and can lead to cylinder scoring.

I'll look at what rear O2 reads, but the bigger question is why you're looking at the wrong sensor? Just log AFR (primary O2) against commanded AFR as well as STFT and LTFT.

Yes for some reason it appears the ecu is getting feedback that engine is running lean ie P0172, as its getting feedback that its lean it will be adding the maxium amout of enrichment it can via fuel trims which is over 30% most likely causing a very rich condition.

As above poster said you rearly need to diagnose the issue, simply scaling the maf to compensate for another fault , if thats the case, will not solve your problem


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I was looking at all of these and they all seemed strange but when I saw zero voltage for a O2 sensor I thought that was causing all the problem since I didn't know it wasn't working on OFT.