P0027 once every 600 miles or so with 2.5T

[gletourneau]

I realize there are quite a few posts and solutions regarding recurring P0027 codes, but I have what appears to be a unique problem that is so far defying explanation for my '05 XC90 2.5t. About six months ago I started to get an intermittent P0027 code related to the exhaust VVT solenoid, and it was at about the time I wanted to replace the timing belt so I went all out and got the large FCP Euro kit with the water pump, tensioner, etc. I went even further and decided to replace both VVT hubs and solenoids in the hopes I wouldn't have to mess with any of this for the rest of the time I owned this car. I was meticulous in timing it and given my age and presbyopia, I even got a borescope to zoom in on the tiny timing marks on the crank teeth to make sure it was TDC, and I used the Volvo cam lock tool to make sure the cams were both where they should be. Everything went smoothly and the nominal, actual and deviation values looked fine in VIDA. Fired right up and no codes. Drove about 700 miles from Virginia to Indiana before the P0027 cropped up again. I'd clear it, and sometimes it would take weeks to come back and sometimes the same day. I used VIDA to check the timing to see if anything was odd, and the operational % for the exhaust VVT would be normal sometimes, and then sometimes cycling. I thought it was probably the ECU running through some tests after I'd cleared the code, but I didn't have a lot of time to mess with it since the car stays in Indiana and I live in Virginia. One thing I did notice was that the wiring harness was getting loose on the exhaust VVT solenoid so I replaced the harness thinking it might be an intermittent open connection or short causing the odd cycling behavior. Still no luck. I removed the solenoid to look for any obstructions in the little strainer in the gasket, but the engine has been very well cared for and the oil and passages are not thick or sludgy at all. I was back in Indiana the other week and decided to second-guess myself and try timing it from scratch again, thinking i must have made a small enough mistake that caused a P0027 only under very specific conditions. So I did that, and I've attached what VIDA was showing me after the timing, after it wanted the exhaust timing to go from 0 to 9 degrees. At zero everything was great, but at 9, the exhaust VVT solenoid keeps fluctuating (the photo caught it at 60%), and it can't get quite enough adaptation to retard the cam by 9 degrees. I can't tell if this is the solenoid failing to let enough oil into the exhaust VVT hub, or the VVT hub (which is brand new) failing. But with these readings, the ECU didn't throw any codes and it ran great.

I drove the vehicle back to Virginia and put another 800 miles on it without any pending codes - until today, when P0027 cropped up again.

At this point, I'm hesitant to believe it's a defective new Volvo VVT solenoid, mainly because I was getting the random P0027 before I replaced it. I'm also skeptical it's the exhaust VVT hub because that was also replaced. I suppose it could be the wiring harness farther back where it goes into the ECU, since i replaced the connector at the solenoid itself. So now I'm wondering if the problem could actually be a glitchy ECU, and there's something else I discovered back in Indiana when the exhaust VVT solenoid was constantly cycling: When I turned the engine off, there was a buzzing noise coming from the engine. Turns out it is coming from the exhaust VVT solenoid. If I unplug it, it stops. Plug it back in, it comes back, almost like a 60hz hum. What could the ECU be doing when the engine is off that would be supplying a signal to the VVT solenoid? If anybody has any ideas or thoughts about this, I'd love to hear them. I love keeping this car around and do enjoy working on it, but this is just getting extremely frustrating.

[abscate]

That’s really an odd one. I think I calculated once the VVT signal is a 200 hz signal , that would sound like a hum. I doubt it is supposed to be active at key off , so that does sound like a faulty ECU

[cn90]

Or ignore it and keep driving it.
Since you already replaced relevant parts...

PS: did you check the screen when replacing the exhaust solenoid?

[erikv11]

Spitballing ...

What oil viscosity do you run?
What's the mileage, could it be an oil pressure problem e.g. worn o-rings on the pickup tube?
What's the health of the PCV system, and crankcase pressure?

These all ignore the hum observation. which if it's the crux of the problem means you don't have to look elsewhere anyway.

[Palmeri11]

Im having the exact issue as you. Did my VVT solenoids, timing belt and both hubs. Retimed it multiple times and still getting the exaust cam timing codes. We are literally having the same experience. I’ve been losing my f’ing mind.


Camshaft Shifting Angle Deviation
• Inlet: -0.09° to -0.03° /
• Exhaust: -9.09° to -4.66°
Camshaft Shifting Angle (Actual)
• Inlet: -0.2° to -0.06°
• Exhaust: 1.42° to 0.09°
Nominal Camshaft Shifting Angle
• Inlet: 0°
• Exhaust: 9°
Camshaft Adaption Values
• Inlet camshaft adaption (6-cyl): 4.95°
• Exhaust camshaft adaption: 9.56°
Other Parameters
• Misfire counter: 0
• Exhaust camshaft reset valve: 80% / 49.8%