it will,
because it uses the rear O2 sensors to read that the cats are working, which they definitely would see right away.
The 2 o2 sensors read the exhaust gas and the rear ones then would see the cat efficiency, which in this case would mirror the front o2 sensors this is a definite sign of insufficient catalyst.
I know they sell a cheater kit which fools the ECM into thinking they are there and working on Mustangs.