Has anyone else experienced this fault before? It is not triggering a CEL, but it is triggering limp home mode (poor throttle response/acceleration, no boost above .3-.4).. This started appearing after an oil and oil filter change.

It is code P0028- Valve Lift Driver Control bank 2. It also showed misfire codes on cyls 2, 4, 6;

Troubleshooting steps so far: Since it also showed misfire codes, I changed all of the plugs, inspected/tested the coilpacks. I also changed out the VarioCam solenoid brackets on both banks, neither were broken or damaged so looks like I've got some spares now haha. I tested the VarioCam actuators using durametric, all function when triggered.

I've logged RPM, camshaft position 1 deviation, camshaft position 2 deviation, and actual camshaft deviation values for both banks to confirm the system functions properly.... Everything looks good. I have not been able to get a log where it triggers the fault; it isn't setting the CEL, and it occurs randomly. Sometimes it goes into limp mode with normal driving, sometimes I can do multiple pulls and drive for a couple of days before it comes back, other times it will pull power as soon as the car starts..

If anyone has any suggestions on where to look next, what to log, or anything to check out I would really appreciate it.

 

well you were that far and not for nothin, i'd have also swapped the cam position sensors also given the codes are ( ?? ) related ( are they not?? ). but if the dura says they're fine. then scratch that completely i suppose. though i trust new cheap parts known to fail before i trust the little gizmo that tells me all is well! but thats just me.

if they aren't, pls disregard. i'm on meds. lol

 

Yeah, I think I'm going to have to take it all apart again and swap the variocam actuators from one side to the other and see if the problem moves to the other bank.. Not really seeing any other alternative now that I'm thinking about it.

 

well, if it helps at all? the cps are only 50$ at pelican. cheapest I've found. they go bad obviously but if memory serves there are cps specific codes, so your idea to swap sides makes more sense diagnostically, than throwing any ( albeit cheap ) part at it. esp since the actuators also go south over time. GL w it.

 

Yeah, I don't think it has anything to do with the Cam Position Sensors, but more to direct VarioCam solenoid/actuators.

To end the thread.. I found a method to trigger the fault, which made troubleshooting easier since I could immediately create the fault then clear it when testing..

Well, I guess I had a loose connection somehow/somewhere. I swapped the VarioCam actuators (the lift actuators located near the coilpacks) from one bank to the other bank, did a hard reset on the ECU (left battery disconnected overnight), and I have not been able to trigger the fault using durametric activations or through driving and I have probably tried it approaching 2 dozen times over a couple hours of running time in the last 2 days. So, something may have gotten knocked loose or tweaked somehow and when I remove and reinstalled, it's all seated correctly now.

Will update if it fails again, but I'm pretty confident that it's resolved.

If anyone finds this thread via search and having this same issue, feel free to reach out to me to share logs and I can help work through it

 

nicely done. you've brought a level of expertise to the troubleshooting that is far beyond the scope of most, myself included. congrats on having it *seemingly* sorted out.

 

Hahah, well, thanks for the vote of confidence, but I jinxed myself by posting that I sorted it out. Drove the car to work this morning and triggered limp mode about a half mile from my office, of course no durametric or logging equipment with me since I thought everything was good to go.

I'll report back if the fault moved to the other bank, or if it remains on the same one when I get home and can test it out and read if there are any faults being triggered... Going to do a pressure test for boost leaks as well while I'm at it.

 

Updating in case this comes up in a search:

After working well through multiple test sessions, the fault did re-appear on the other bank indicating a failed VarioCam hydraulic actuator pn 996-105-301-72, #25 in the attached diagram.

Easy fix.

Follow any spark plug change DIY, remove the 2 coilpacks that block the bolts on the actuator (there is one actuator for each bank in the spark plug valley, between the rearmost and middle coilpacks), remove 2 10mm bolts, unclip wiring harness by pressing down on silver clip and pull. Bracket will slide off, then pull the actuator out. It is in there pretty firm/tight. There will be some oil leakage from the port where the sensor comes from, but not much; the area the oil runs off is going to end up dripping onto your exhaust manifold/turbos, so don't be surprised for a smoky start up upon reassembly. Insert new actuator, be sure that the notch on the wiring connector is on the top. Not sure that it really matters, but both were aligned in that manner, and it makes reconnecting the wiring harness easier. Assembly is reverse of removal. If anyone is interested/needs pics or help with the procedure, feel free to contact me. I can do a DIY with pics if necessary, but I feel it is pretty self-explanatory.