Secondary O2 sensor needed for Cruise control?
 

Backstory first...

Removed my secondary O2 sensor from my Borla UEL and installed a wideband sensor in its place. I have an ECUTEK tune, so I figured that the secondary oxygen sensor checking is removed and I thought nothing of it.
The next day I start the car and begin to drive. The CEL comes on after a few minutes, and when I press the cruise control on/off switch the cruise control light comes on but will NOT turn off. The wideband is also reading a rich air/fuel ratio (13.2) at idle when the car should be in closed loop (fully warmed up etc.)
Its almost as if its stuck in open loop or some sort of catalyst self-test mode where it runs rich at idle and doesn't use primary O2 sensor to trim fuel

WOT shows normal A:F of low 13's so I believe the wideband is getting accurate readings.

Does the ECU need the secondary O2 hooked up for some reason?
I know there was a thread stating that you don't need the secondary (as is common on older OBD-II cars), but it is creating some strange problems for me.

Anyone with any input?

I'd just have an extra bung welded on for your wideband. I imagine any exhaust shop should be able to do it for you.

I would rather just use the available bungs on the header due to them being there and my not needing a secondary O2 sensor anyways....

I may just make a dummy plug to simulator the secondary sensor and have it plugged in so the ECU thinks its there.

I just find it hard to believe the ECU will disable cruise control and make the car run rich without the secondary O2 plugged in

Its probally a fail safe, the O2 sensors are heated and and the car will stay in open loop mode until warmed up. In this case it can't read the second 02 so it stays in fail safe not allowing cruise and running rich.

You may have to ask specifically for the downstream HEGO sensor check to be disabled in your tune, it may not be there by default. Check with your tuner.

Cruise control is more than likely disabled when the vehicle is in a limp mode, or has DTC's to be cleared, in the interest of safety.

I think a resistor will fix it, but I don't know how many ohm's of resistance it is.

13.2 isn't "rich" mid to low 12's or 11's or 10's is rich and getting richer.

13.2 is pretty spot on IMO

On the cars I have tuned, closed loop idle target AFR is 14.7 unless the FRS/BRZ is different

My main concern/question is that it looks like the ECU is running open loop with a missing secondary O2 sensor, to which there is debate about if the secondary O2 sensor is actually used for minor fuel trim adjustments on subaru engines.

I will plug in the seondary O2 tonight when I get home and see if it fixes the idle AFR readings

In terms of stoichiometry 14.7 is a lean mixture

14.7 is correct for target closed loop afr. Unless it has been specifically altered somehow.

For pure gasoline 14.7 is Stoic, but with ethanol added (common 10% ethanol fuel) the "stoic" ratio is less. However, I still believe that the ECU has a target AFR of 14.7:1 at idle/cruise in closed loop operation

As far as I know, all cars shoot for Lambda = 1 in closed loop... unless some are compensating for 10& ethanol in their fuel, which would be around 14.2:1 stoic which may explain my "rich" readings

That's not always the case these days, although generally in the past it was when cars were only fitted with narrow-band HEGO sensors.

A lot of modern vehicles have wide(r) band sensors fitted and closed loop targets away from lambda 1.0.

Any cel disables cruise control.

Lots of good info in this thread.

Does any of the tuners on here familiar with this platform specifically know what the target lambda/AFR is during closed loop operation?

Also this is my first drive-by-wire car, so I did not expect cruise control to be disabled if there is a DTC code present... but it makes sense in a way.