Veronica

iTrader: (2)

I am chasing a 'second O2 sensor too lean code' which occurs when ambient temps drop below 50deg. It may trigger a code one mile after driving or on the highway... Pretty random... When the cold weather (<32deg) hits - I disco the battery and reset the ECU. This seems to satisfy the parameters and I generally do not get the SES again until ambient temps warm again... During the summer - no SES/all good! If I put the OEM cat back on (for emissions test) no SES. I cannot just turn off the rear sensor and turn back on for testing...

As I monitor the front and rear O2 sensor data as I idle and rev it when (engine warm / in the driveway/ 52deg ambient) I see a few things:

1. The rear O2 sensor 'tracks' the front sensor value and is pretty consistently .2mV below it. So as the front reads .9xx the rear is .7xx...

2. The rear sensor 'lags' the front sensor changes. The rear will even show 0.0 until it starts climbing again to catch up with the front sensor reading...

3. The front and rear values change quite rapidly from .1 to .9 and are constantly going all the way up and down (either idling or if I rev it). It never 'stabilizes' and centers around a value (like .6) with minor adjustments "like I would expect to see"...


So my questions are:

What is a normal delta between the front and rear O2 sensor readings? Is .2mV about right?

Is rapidly changing through the range of values normal - or does it indicate a FPR issue? S/W issue? Bad O2 sensor/wiring issue?

Should the rear sensor ever report below .2mV? It goes to 0.0 and may dwell there a moment...

What other parameters should I monitor at the same time?


(I do not have a wideband and I do have the GST w/ Pill and TBE tune (although I am not quite a complete TBE - I do have test pipe and an opened up OEM muffler (for less resistance) )

Any help is appreciated!

4bangn

your front O2 (sensor 1) is the important one, that's the one the ecu goes off of for air/fuel, the rear O2 (sensor 2) does nothing and is just there for emissions, if you have a test pipe (cat delete), you will get codes for the rear O2, the fix is to use a fouler, there's a few threads on here for this, I know this issue very well as I had the exact same problem, as soon as I installed the fouler, engine light never came on again

Veronica

iTrader: (2)

Yep.

I have the 'mini cat' for the rear O2 sensor and I don't get the SES light during the summer...

I may try a non-fouler next, but I am not sure there isn't something else going on...