This is from a Honda service tip dated 03/01/2005:
DTC P2647: VTEC Oil Pressure Switch Circuit High Voltage
SOURCE: Honda Service News
TITLE: Replace VTEC Oil Pressure Switch for DTC P2646, P2647
APPLIES TO: 03-05 Accord 4-cylinder03-05 Element
02-05 CR-V
SERVICE TIP:
Got a vehicle in your shop with either of these DTCs?- DTC P2646 (VTEC oil pressure switch circuit low voltage)
- DTC P2647 (VTEC oil pressure switch circuit high voltage)
Replacing the VTEC oil pressure switch usually fixes the problem. If it doesn’t, then press on with normal troubleshooting.