I wrote about this topic more in depth over at the element website (https://www.elementownersclub.com/t...6-wiring-and-oil-pressure-revisited-is-the-factory-service-manual-wrong.168910/) but I thought I’d tackle it in a different way over here since it seems people are seeing vtec pressure switch codes (P1259, P2646, P2647) more often on second gen CRVs now.
I wanted to explain how a basic automotive sense circuit works, and the vtec pressure switch happens to be one of them. It is a so called “pull up/pull down circuit”.
the top picture is a snippet from a service manual. It shows the vtec pressure switch circuit, and the second picture is my rendition of it to make it easier to visualize.
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The PCM has the ability to put voltage on a wire. It also has the ability to sense the voltage on a wire.
So PCM puts 12v on the VTPSW wire. The wire is routed to the VTEC Pressure switch. When VTEC is off, there is no oil pressure. When there is no oil pressure, the VTEC pressure switch is in closed circuit (Ie continuity, aka ON status). There is another wire that goes from the VTEC pressure switch to ground. So when VTEC is off, there is no oil pressure, the switch is on, and the wire is continuous to ground. Because the wire goes to ground, there will be 0 volts on the wire sensed by the PCM.
So PCM puts 12v on the VTPSW wire. The wire is routed to the VTEC Pressure switch. When VTEC is on, there is oil pressure. When there is oil pressure, the VTEC pressure switch goes open circuit (Ie no continuity, aka OFF status). There is another wire that goes from the VTEC pressure switch to ground. So when VTEC is on, there is oil pressure, the switch is off, and the wire voltage never reaches ground. Because the wire never goes to ground, there will be 12 volts on the wire sensed by the PCM.
You can see what the PCM sees on a scan tool. If you have live data on your scan tool, you should be able to see VTSOL (vtec solenoid activation, abbreviated VTS sometimes) and VTPSW as data parameters.
When the car does not want VTEC, your VTSOL will read OFF and your VTPSW will read ON. When The car activates VTEC, the VTSOL will read ON and the VTPSW will read OFF.
Anytime there is a situation where VTSOL = OFF and VTPSW = OFF you will get a P2647. Anytime there is a situation where VTEC SOL = ON and VTPSW = ON you will get a P2646.
In layman’s terms, when the car doesn’t need vtec it expects the pressure switch to say that there is no pressure. When the car activates vtec, it expects the pressure switch to say that it sees oil pressure. If there is a mismatch, the codes get set and you go into limp mode.
Anyway, I hope this made sense, and helped the DIY guys learn a little more about computer sense circuits. You can see this type of computer sense circuit all over the place, and I think knowing how a “pull up/pull down” sense circuit works can make your diagnostic skills better.
I wanted to explain how a basic automotive sense circuit works, and the vtec pressure switch happens to be one of them. It is a so called “pull up/pull down circuit”.
the top picture is a snippet from a service manual. It shows the vtec pressure switch circuit, and the second picture is my rendition of it to make it easier to visualize.
The PCM has the ability to put voltage on a wire. It also has the ability to sense the voltage on a wire.
So PCM puts 12v on the VTPSW wire. The wire is routed to the VTEC Pressure switch. When VTEC is off, there is no oil pressure. When there is no oil pressure, the VTEC pressure switch is in closed circuit (Ie continuity, aka ON status). There is another wire that goes from the VTEC pressure switch to ground. So when VTEC is off, there is no oil pressure, the switch is on, and the wire is continuous to ground. Because the wire goes to ground, there will be 0 volts on the wire sensed by the PCM.
So PCM puts 12v on the VTPSW wire. The wire is routed to the VTEC Pressure switch. When VTEC is on, there is oil pressure. When there is oil pressure, the VTEC pressure switch goes open circuit (Ie no continuity, aka OFF status). There is another wire that goes from the VTEC pressure switch to ground. So when VTEC is on, there is oil pressure, the switch is off, and the wire voltage never reaches ground. Because the wire never goes to ground, there will be 12 volts on the wire sensed by the PCM.
You can see what the PCM sees on a scan tool. If you have live data on your scan tool, you should be able to see VTSOL (vtec solenoid activation, abbreviated VTS sometimes) and VTPSW as data parameters.
When the car does not want VTEC, your VTSOL will read OFF and your VTPSW will read ON. When The car activates VTEC, the VTSOL will read ON and the VTPSW will read OFF.
Anytime there is a situation where VTSOL = OFF and VTPSW = OFF you will get a P2647. Anytime there is a situation where VTEC SOL = ON and VTPSW = ON you will get a P2646.
In layman’s terms, when the car doesn’t need vtec it expects the pressure switch to say that there is no pressure. When the car activates vtec, it expects the pressure switch to say that it sees oil pressure. If there is a mismatch, the codes get set and you go into limp mode.
Anyway, I hope this made sense, and helped the DIY guys learn a little more about computer sense circuits. You can see this type of computer sense circuit all over the place, and I think knowing how a “pull up/pull down” sense circuit works can make your diagnostic skills better.
