Subaru VVT signals

I am trying to get a handle on the "how" VVT sensors in an 08 Subaru speak to the ECM. Is there a variable signal or is it simply a constant open/closed one between the VVT and the oil pressure switch? What does the ECM do in response to this code and how does it adjust the engine to compensate? I am looking to do some fankenstein work and wish to understand all various communications, this VVT module is the one I am less knowledgeable around.

Hey JerryO! Sorry for not getting back to you sooner. I'm moving this to the Diagnostic Tools section, FYI.

Just to be clear, are you referring to this video?



Just to have something to refer to, I looked up the VVT system on a 2008 Subaru Forester 2.5L:



We're calling it VVT, but I'm fairly sure it's actually a variable lift system, FYI. From what I understand, these switches are normally closed, and open in the presence of adequate oil pressure. There will very likely be rationality logic at work there, i.e. if it sees an open switch (high pressure) KOEO, it'll flag a code. OR, if it sees the switch closed (no pressure) with the engine running, code. Knowing which YMM you're looking at specifically will make it easier to research the PCM fault strategy.

There is no separate VVT module on this setup, as far as I know? But usually, with any kind of valvetrain code stored, the PCM shuts off the oil control solenoids.

Yes, that is the video that caught me and you website. See what I am doing is trying to switch an older engine (earlier 2000's or even further back) into this car and without those controls on the heads I suspect trouble. What I am trying to learn is how to communicate with the brain so it doesn't have faults. There is no oil pressure sensor on the heads of these engines either. There is the main oil pressure sensor on the engine short block, which is being used but also possibly spliced into if there was good reason. If I drop an older longblock into the car and bolt down the exisiting intake these switches and sensors on the heads seem to be my biggest obstical. If I can understand the communication maybe I can create a small ciricut board (or something even simpler) to accomidate this.

I gotcha! For our info, what's the specific YMM of the receiving car, and the YMM of the donor engine?

For the record, it's my experience that these kinds of swaps are... challenging. I'm not saying it can't be done! Just that this variable lift system isn't the only thing you'll have to make work. Not trying to be Captain Obvious. :lol:

If the goal is to keep the check engine light off, then I see a few different things you'll have to do. One is fool the PCM into thinking the variable lift solenoids are installed so you don't get circuit codes. The easiest way would be to simply leave the solenoids installed on the wiring harness, but zip tied out of the way somewhere. That way, the PCM thinks those circuits are electrically working.

Second might be that oil temperature sensor we see in the diagram. I dunno if the older engine will use that sensor or not? Also not sure what kind of testing the PCM uses on that sensor besides basic circuit tests. Knowing the YMM will help.

Third will be those oil pressure switches. Again, knowing YMM will help us do research on how the PCM tests these switches.

2009 Outback with a 2002 long block. But for entertainment even a 1995 2.2L longblock. With intake manifold adaptor plates dropped onto the heads. It really shouldn't matter. This is and possibly the EGR are the only thing I see older engines really don't have. The rest is all manifold.

The oil temperature sensor on this 09 Outback 2.5L I can not find. I have another 07 Impreza engine laying around here and its the same 2.5L, I don't see the sensor on this either. And I doubt the earlier engines (1990 - 2004) have oil "temperature" sensors as well. Unless the other plug on each head is a temp sensor and not a pressure sensor.

Attached are photos of the 09 VVT portions of those heads like in the video.

The oil pressure switch you write about is used by the ECM to diagnose issues with the oil switching solenoid switching valve. The OSV or oil switching valve is a duty controlled solenoid. (Pretty sure) When the computer commands the OSV to open oil pressure is fed to the VVL (Variable Valve Lift ) system. If the solenoid actually open and oil flows, the valve train switches to high lift mode. At the same time that same oil pressure also open the oil pressure diagnostic switch. This tells the ECM that the solenoid mechanically opened and the oil pressure should be high enough to switch the valve train to high lift mode. If the ECM commands the OSV to open and pressure switch does not open, that means no oil has flowed. That could mean you have a mechanically stuck closed solenoid, clogged filter screens in the manifold that the solenoid attaches to, or even a defective switch. I do not believe the ECM can monitor if the valve train actually switches.