As far as clearing the codes in the ECM you can with no problems but remember if the fault is still present the code will return either in history or active. Even after you repair the fault you still need to clear the code or after about 25-35 ignition cycles if the fault has not returned the ECM should clear itself. Be glad that the C5 has the option for you to clear troubles because with other OBD II
systems you need a scanner just to clear the codes to get the check engine light to go out. Hope this helps