Thanks for the info. I take that you meant the O2 sensor was the one event that you thought could light up the CEL without throwing a code.

I did checked the 02 sensor with a scope on the X11 connector. The on/off ratio was in range at both idle and high RPMs, so the chance was high with intermit cable/connectors. I will recheck all the connections. Well, it is way passed 60K miles with my current O2 sensor, maybe, I go ahead and replace it.

Thanks again

__________________
Kachun

1990 300SE
2003 E320