The Honda name has been synonymous with high-tech solutions for longer than most people on Earth have been alive -- and for good reason. Honda, like many manufacturers in post-war Japan, had to create a competitive edge among more established companies by being clever, bold and more flexible than they. Code P1259 signals a problem with one of the company's trademark systems; one that's a lot more specific than it sounds.
This manufacturer-specific code sounds very cryptic and very bad -- Honda lists P1259 as "VTEC System Malfunction." At its core, the VTEC system is essentially a second set of lobes on your intake camshaft. At low rpm, the smaller lobes on the camshaft actuate the intake valves, enhancing low-rpm torque and fuel economy, and decreasing emissions. At high rpm, about 4,500, the VTEC system goes "on the cam," and you get that familiar kick-in-the-pants sensation of a sudden power increase.
The lobes on your intake camshaft move the valves via small levers called "followers." The followers on a VTEC engine are lower-case "h" shaped. The bottom of the tall left leg of the "h" rides on the smaller cam lobe, the top of the long leg pushes down on the valve, and the shorter right leg swivels on the long leg. That shorter leg rides on the big camshaft lobe. When VTEC kicks in, an oil-pressure-powered cylinder locks the two legs of the "h" together, thus driving the cam follower with the larger cam lobe. The VTEC system requires around 55 psi of oil pressure to work, though this may vary somewhat by the specific car.
The oil pressure switch is one of the two primary switching components of the VTEC system; it's the component responsible for telling the computer if there's sufficient pressure to engage the VTEC system. The OPS is actually a redundancy specific to the VTEC system; the engine's primary oil pressure sensor tells the computer what's going on with the motor. So, if this switch says that oil pressure is low while the primary pressure sensor says pressure is normal, then the switch may be malfunctioning and throwing a code. If the harness connector for the pressure switch is getting power from the battery and there's continuity (some resistance in ohms) between the terminals on the switch harness, then move on to check out the VTEC solenoid.
The VTEC solenoid is the electrically controlled valve that opens to send pressurized oil to the cam followers. It works much like any other pressure solenoid, using a coil of wire to induce a magnetic field and open the valve armature. This solenoid is, for all intents and purposes, the "heart" of the VTEC system, and a failure here will certainly trigger a code. After you check the OPS, unplug the solenoid wiring harness and use a multimeter to check the ohms of resistance in the solenoid valve. When you touch thee ohmmeter probes to the solenoid terminals, you should see between 14 and 30 ohms; anything outside of this indicates a bad solenoid. Again, the specific figure will vary by application, but you should never see either 1 ohm or 10,000 ohms.
