I have an 02 accord that has the check engine light on. Its got 145000 miles on it. I got it scanned. The codes were p1259 vtec system circuit fault bank 1, p0420 catalyst system efficiency below threshold bank 1, and p1457 evap control system leak detected(canister). I cleared the codes and will see if/when they come back on, but if you have any ideas on what they might be I would appreciate any advice. Thanks!

Here is the explanation from engine-codes.com

P1259 Honda Description
The VTEC system activates the VTEC solenoid valve by command from the powertrain control module (PCM), and it charges/discharges the hydraulic circuit of the VTEC mechanism that is installed in the valve system to switch valve timing between Low and High. The PCM monitors oil pressure conditions in the hydraulic circuit of the VTEC mechanism according to the VTEC oil pressure switch downstream of the VTEC solenoid valve. If there is a disparity between oil pressure condition in the hydraulic circuit that is determined by the PCM command, and the oil pressure condition that is determined by the status of the VTEC oil pressure switch, the system is considered faulty and a DTC is stored.

Read more: http://engine-codes.com/p1259_honda.html#ixzz3aiInXy9j

P 1259 VTEC oil pressure switch circuit or vtec solenoid or valve,Here the situation you can be dealing with the oil pressure switch or the VTEC solenoid or valve,

low oil level can cause this as well as a bad oil pressure switch for VTEC control, possible VTEC solenoid.
Another reason for this code is the immobilizer. the anti theft device that looks at your key for the diode to match the car. This is on cars with out the VTEC.
On the VTEC system
DEFINITION:
VTEC System Malfunction

PROBABLE CAUSES:
-Low oil/pressure
-Blocked oil pressure
-Failed VCT oil control valve

Yes, the codes do indicate the problems and certainly lack of power.The P1259 is set when there is a problem in the VTEC Oil Pressure Switch circuit or VTEC Solenoid Valve circuit
P1164 and 1149 are both Faulty Air/Fuel Ratio Sensor 1

If the CEL is not on, then the problem is intermittent. The first step is to locate the VTEC switch and A/F Ratio sensor, and verify the connections are OK. Having both of these fail together would be odd. I suspect the main culprit is the VTEC Oil Pressure Switch.

p1259 is a problem with the VTEC system. this system is for improved performance at higher rpm's. oil can get sludged up and clog the system, or the VTEC solenoid can just go bad. you can always have someone with a scan tool clear the codes to turn off the light, but until the problem is fixed, it will just keep coming back on

The P1259 : is problem in the VTEC Oil Pressure Switch circuit or VTEC Solenoid Valve circuit.
check the wire on the VTEC Oil Pressure if it's loose.

1.1 o2s(ho2s)(s1) = eng
3.2 map circuit = high input eng
7.1 t p sensor(a) = voltage low eng

P1259 is a code for vtec malfunction usually cause by a bad vtec solenoid, vtec pressure sensor, low oil level, bad connection. Was oil change done? May want to check the oil level. P1166 is a code for a primary o2 sensor 1.