After adding headers and tying up the second set of O2 sensors on my 2000 Box S, the inevitable has happened. CEL, P-codes are 0139, 0159, 0156, and 0153. Essentially, because the second set of sensors never warms up, the DME isn't happy. The car runs fine and has a nice chunk of additional power through the mid range. Burns a bit more fuel, though
.I've hollowed out the second set of cats, so I'm not concerned about those clogging and fouling, and the car is primarily for AX/spirited driving, so I'm fine clearing CEL's every now and then and getting along with it. I will be saving some cash to have the ECU remapped to make the most of things, though.
Cheers!