Well...I have been driving the car for the last 26000mls and the CEL has been 'on' a few times(5 to be exact) with knock sensor fault(it happens when I realy step on the gas
...we need 96 octane not 93)but passed smog a month ago and has been off for the last 4k or so...
CEL 'on' does NOT make any difference in performance or MPG...
Will keep You posted...