Or will it only cause boost creep?
Yeah the 32bit ECU's require the rear O2 to function properly.Cobb does recalibrate the threshold so you can run with aftermarket exhaust,but the DTC I guess is not totally disabled so you still know if there is an issue witih the sensor. That sensor does provide AFR feedback that helps with fuel trims. The older 16 bit ECU's can easily run without the rear O2 as it is strictly for cat efficiency. I haven't had a rear O2 for over 4 or 5 years now.I'm getting That 0137 right now. I asked Eric at TP about it this morning, he indicated I may need a new rear o2. Which sucks because the car is a few months old.