My car is a 2006 s2000 with an aftercooled CT engineering supercharger. It has been modified to run 12psi along with supporting mods (fuel pump, fuel rail, injectors, fuel return line, and flash pro etc etc).

Many have reported trouble getting the catalyst monitor to set, something I could relate to. Although the car never threw any CEL codes, I replaced both 02 sensors, and bought a new catalyst. After failing to resolve the issue by throwing parts at the car, I have traced the problem back to my PLX wideband.

My theory...When I installed the PLX wideband, I cut the wire going to the ECU for the ECT2 and I tapped into it for my wideband signal. Now the problem with this is the ECU is checking for certain parameters to be met in order for the catalyst monitor to set. One of those parameters is the engine coolant temperature, but if the ECU is not seeing one of the ECT signals then it will never set!

I have reconnected the ECT2 wire and the monitor is now set. Could this be purely coincidence? I have no idea but I hope this will help some of you out there. Cheers