Front codes can come from the headers themselves. The best
suggestion I've seen recently is to raise the closed loop enable
temperature to near your minimum ECT (thermostat) to hold
off trying the O2s until things are good and hot. Switching
codes are the first to fall, if you have an exhaust cooling kind
But you do have to be more specific about which of the hundreds
or so codes, about 20 just for O2s, you mean.