DTC P1607: Pcm Internal Circuit
WARNING: This page is about a different car, the 2000 Honda Civic. However, it is still accessible from the selected car via links, so may be relevant.
Perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING DTCS in SELF-DIAGNOSTICS - INTRODUCTION article. Turn ignition on and wait 10 seconds. If DTC P1607 is not indicated, problem is intermittent. System is okay at this time. If DTC P1607 is indicated, substitute a known-good PCM and recheck. If symptom or problem goes away, replace original PCM.