Some 2002-04 RL and NSX models may illuminate the Check Engine light and store trouble code P1456 (EVAP control system leak) in PCM memory. One likely cause, says Acura, is a loose fuel cap. Damaged fuel filler pipe threads may be the ultimate villains.
To make a definitive diagnosis, remove the fuel cap, then tighten it. The cap should turn freely until the O-ring seats against the fuel filler pipe. If it does, this information doesn't apply; continue searching for the cause of the leak. However, if you feel resistance or the cap binds before the O-ring seats, the filler pipe threads are most likely damaged. Installing an upgraded fuel filler pipe should eliminate the EVAP leak. Order part #17660-SZ3-A50 for RL models; part #17660-SL0-A50 for the NSX.