I have heard several diferent concepts on this issue. I have even talked with the folks at Buschur about this particular issue as well for closure. Has anyone found evidence that using a testpipe and trigering the CEL will force the ECU into "safe mode"? Elaborate.

 

I have a ghetto test pipe on my Evo, and the check engine light is on, and I'm still pulling decent times at the track. I doubt the car runs in safe mode for the 2nd O2.