Originally Posted by
Flexray
P2647 sets when the VTEC oil pressure sensor sees pressure when the VTEC solenoid is not activated. This is how I would diagnose this problem.
I would let the vehicle sit over night so it is stone cold. With a scan tool, I would pull up the VTEC solenoid activation and the pressure sensor data before starting the engine. Once I'm ready, start the engine and command the solenoid on and off rapidly while watching the pressure sensor, every time the solenoid is activated the sensor should see pressure. If the solenoid is command on and no pressure is seen or commanded off and pressure is still seen the solenoid is jamming. The spool valve on the solenoid is a very close tolerance valve, as the engine warms up the tolerances expand making it less prone to jamming. If you do not have a scan tool, you can jump power to the solenoid and monitor the pressure sensor with a volt meter, but the engine module powers the solenoid by pulse width modulation, jumping direct power to it won't fully replicate how the valve normally works.
If the solenoid jambs, remove it off the engine and inspect the oil inlet screen. If it is broken the bits of screen will go through the solenoid and rocker arm plungers and basically damage everything. The spool valve should not have any marks or scoring on it. If something is eating it's self inside the engine, the debris and metal will jamb solenoids.
If the blue/black wire on the pressure sensor has a short to ground, the engine module will think the VTEC system has pressure in it. Back probe the blue and black wire and test for ohm's to ground while wiggling the whole engine wiring harness bit by bit, you should have no ohms to ground at anytime on that wire.
Hope this helps.