P2646 = Rocker arm pressure switch low voltage

Possible causes:

Check engine oil level, oil condition and pressure

Faulty Variable Valve Timing and Lift Electronic Control (VTEC) / Rocker Arm Oil Pressure Switch

VTEC/Rocker Arm Oil Pressure Switch harness is open or shorted
VTEC/Rocker Arm Oil Pressure Switch circuit poor electrical connection

The specific repair cost will vary based on the actual cause.

First step would be to check the engine oil level, refill as necessary. Zero cost so far...