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Unsolvable engine codes

18K views 26 replies 9 participants last post by  1-3-2-4 
#1 ·
My 06 Tribeca has been in 2 different shops in 90 days for engine codes P0026 and P0028. The first shop (NAPA) said the battery was bad and replaced with new free of charge. The second shop (Subaru dealer) replaced left and right side OSV solenoids.......didn't fix. After they went thru the "official Subaru" flowchart and called Subaru tech support (who say this problem is rare) they have arrived at the ECM module. They don't know if this will fix it but no other choice ($800 new and uninstalled or $250 used and installed). I told them go for the used at this moment but not installed yet. The vehicle drives great except for if you do heavy accel (dropping 2 gears) the motor cuts out like hitting a rev limiter until you let off gas............don't know if related to the codes.

Any help or advice about this would be awesome...........tired of going to the shop
 
#3 ·
#4 ·
From the technician reference book:
"At high engine speeds, the lift is increased to reduce intake resistance and to obtain higher power. To protect the engine, the system does not allow racing up the engine to high speeds in P or N range."

Hypothetically, when you floor the accelerator at speed, the ECM sends signals to both the TCM (to downshift) and VVL (to increase lift, i.e. engine power)... if the TCM functions but the VVL doesn't, engine cut-out would certainly seem related to the codes.

That said, I agree with Dodik.... the first thing that should have been looked at is the oil pressure switch; however, to have both VVL solenoids fail at the same time seems odd, if not extremely coincidental. There are two common failure points between the RH and LH VVL solenoids, the 16-pin brown engine wiring ("B20") connector (located behind the RH side of the engine above the vacuum pump) and the ECM itself.

You could have a loose connection at the ECM (B134) or B20 connectors; however, this would probably cause additional codes as the B20 assembles the signal wires from VVL oil pressure switches, cam position, knock and oil temp sensors and throttle control going to the ECM and the B134 is a 34-pin connector that has even more sensors attached to it. Therefore, ECM replacement seems to be the most likely (though not a guaranteed) fix.
 
#5 ·
P0028 is a fault code related to the functioning of the left (driver) side variable valve lift mechanism (VVL).

The VVL system uses an ECM-controlled solenoid to control oil pressure to a mechanism on the camshaft that changes the lift of one intake valve in each cylinder. The operation of the solenoid is monitored by an oil pressure switch; when the ECM is calling for "low lift" the solenoid is essentially closed, the oil pressure to the camshaft mechanism is low, and the oil pressure switch remains closed (low resistance across it's internal contacts). When the ECM is calling for "high lift" (typically at higher engine rpms while cruising), the solenoid allows more pressure through to the mechanism and the switch opens. The OBD checks that when the pressure is supposed to be low, the switch is closed (low resistance), and when the pressure is high, the switch is open (high resistance). The code can be triggered if the ECM command state and the switch don't agree.

The P0028 can be caused by a problem related to the solenoid, i.e., solenoid isn't functioning properly. However, there are cases here where that code (or the P0026 for the right side mechanism) was traced to a defective oil pressure switch. In some cases the switch contacts develop high resistance and they appear to the OBD to be open all the time. This could be caused by corrosion, or oil leaking past the internal seal and contaminating the contact surfaces.

See Variable Valve Lift oil pressure switch resistance for more details and photos of the solenoid and switch on the left side.

Also, search for codes P0026 and P0028. There's a good number of posts, as well as discussion about replacing the switch and, especially, avoiding cracking the head.

From here: http://www.subaruoutback.org/forums/66-problems-maintenance/245473-code-p0028.html
 
#6 ·
reply

I agree that it is very odd both solenoids were bad at same time. The oil only has 1000 miles on it and no crude was found by dealer (Subaru told them to check for that). I bought the vehicle from a different dealer but the vehicle had all service from new at the dealer where I'm getting work done. They pulled maintenance records and previous owner had all maintenance work done there and was "very well maintained". They found in records that it had been in for service lights but they just reset the codes. I will have them check oil pressure switch..........thanks for the insight from all!!!!! Isn't oil pressure switch in the Subaru flow chart??
 
#8 ·
I agree that it is very odd both solenoids were bad at same time. The oil only has 1000 miles on it and no crude was found by dealer (Subaru told them to check for that). I bought the vehicle from a different dealer but the vehicle had all service from new at the dealer where I'm getting work done. They pulled maintenance records and previous owner had all maintenance work done there and was "very well maintained". They found in records that it had been in for service lights but they just reset the codes. I will have them check oil pressure switch..........thanks for the insight from all!!!!! Isn't oil pressure switch in the Subaru flow chart??
It's the second item on the flow chart. However, I think it's mostly irrelevant at this point since both sides are showing trouble.

Each VVL solenoid has its own, independent oil pressure switch, so if both sides are throwing codes, you're either a victim of dumb luck or something in common (e.g. ECM) is failing.

Someone correct me if I'm wrong here, but in reading through the tech ref book, my understanding is that low oil pressure throughout the engine would not necessarily trigger the VVL pressure switches on its own... the VVL switches are "diagnostic" in nature and sense the pressure in its respective VVL system only (which varies from nominal engine oil pressure), so unless the oil pressure light on your instrument panel is on, there has to be some malfunction, blockage, etc. in the VVL system for 0026 or 0028 to be triggered. If both are triggered without the oil pressure light, I'd look for the common link between the two, not the solenoids or switches themselves. That's what your dealer has done, and if they consulted SOA, I'd be feeling pretty good about the ECM swap.

Jumping right to the ECM can be a sign of a lazy or incompetent mechanic, especially since failure rates are so low... but in this case, I think your dealer has made a dutiful and proper diagnosis, and I certainly wouldn't fault them if it turns out not to be the ECM.
 
#9 ·
There isn't any low oil pressure light on. Are Subaru's finicky about the oil and filter used? Not sure what the previous used car dealership put in it. Thought about having the oil and filter changed when the ECM put in next week. Have noticed if vehicle sits for a day or more the service engine lights won't come on until it's driven for a few blocks. How could I post a video so you can hear what it does under heavy acceleration? Thanks
 
#10 ·
Upload the video to YouTube and post the link here.

Subaru is renowned for their oil filter having a higher bypass pressure than standard aftermarket filters. IIRC, the OEM operates around 23 psi whereas most off-the-shelf are around 10-13 psi. Essentially, the OEM filter's bypass will operate less frequently, which means more oil will be going through the filter media. This seems like a big deal, but the psi rating on the filter is the differential across the media (i.e. it isn't triggered by the system oil pressure). Simply put, the bypass is a failsafe in case the media clogs, and since dirty oil is exponentially better than no oil at all, every oil filter on the market is manufactured with some sort of a bypass.

In theory, if your oil was clean and free of solids, your oil filter would never clog and therefore, it would make absolutely no difference what the bypass was set at. But that's not reality... we all get "gunk" in our oil to a certain degree; of course, that's why we have oil filters. Personally, I see no issue with using an aftermarket filter provided a) both the oil and filter are changed regularly, and b) you don't have any oil-related issues with the engine (e.g. excessive bits of metal/corrosion, carbon, etc. in the oil).

That said... there are two schools of thought on the matter: 1) the premium for OEM is worth it, even if it doesn't make a difference and 2) it makes very little difference whether you use the OEM filter or a quality, aftermarket filter. The overwhelming consensus, however, is that if you're still under warranty, you always use the OEM. But many Subaru owners report having used even the el cheapo Fram filters forever without any issues. For the record, that's what's on my Tribeca right now. YMMV.

As far as type of oil... frankly, anything that meets the OEM viscosity, ILSAC and API ratings is fine. Brand makes very little, if any, difference. Synthetic vs. conventional makes very little, if any, difference. (Again... provided regular changes of oil/filter.) Anyone who tells you otherwise is a sucker for marketing. For the record, I'm currently running the economy Shell conventional brand that I buy at Menards for $30/case when it goes on sale, and not only has my oil leak stopped, but I'm also burning less oil than when I was using Mobil 1 synthetic.

Unless the oil and/or filter hasn't been changed in a while - barring other oil-related issues with the engine - I wouldn't be too worried there; nevertheless, when buying a used car, the first thing anyone should do is change the oil/filter, even if the seller told you they just did a week prior. It doesn't hurt to change it now and see if the problem goes away... even if it doesn't help, you're going to have to change the oil at some point anyway (and probably should have already), so there's no "cost" to the slightest possibility that it is being caused by the oil/filter, which is, after all, a common link between the OSVs.
 
#12 ·
^ +1. It's a WAAAAAY too late light, if it's anything like the ones on modern turbocharged Subies.

Virtually all modded Subies carry a direct-measured oil-pressure gauge. The well-modded ones use gauges which integrate/interface their own preset warning visuals/audibles.
 
#13 ·
UPDATE:
The ECM was changed because dealer recommended...........lasted 5 miles. Now I have error codes P0016, P0018, and P0026. I'm having Subaru dealer change the oil when the keys/fobs are reprogrammed today.............another issue is step on gas above 40 mph and engine rpms stuttering/jumping @ 4000...........if you keep on gas when it does that car starts jerking badly........but let off gas just a little bit it stops jerking and calms down........I have a video I can send via email if you can help
 
#16 ·
hey subzero... any progress on this? I am having a similar issue. I have changed both valves and the pressure switches. Done flushes and still getting the error codes. Mine are mostly on the passenger side P0011, p0016 , p0018 but sometimes it throws codes for both sides. Just curious what happened here.
 
#17 ·
16, 18 and 11 together would seem to point me at the timing components (chain) as that's the thing that turns them all together. Or general electrical problems (bad ground, bad battery, bad alternator).

I'll be interested to hear what others think.

Any recent issues with your car WinoOutWest? Recent work?
 
#18 ·
I ALWAYS get 11, sometimes get 16 and 18 although they are usually together when they do come up. Sometimes 21 is there as a pending fault but its it rare.

I "took over" the car from my brother in June of this year. It had just started throwing this code and his mechanic changed the one solendoid on the passenger side. It was only throwing the code once every few weeks back then.
Now it is daily. I have changed both solenoids and pressure switch on the passenger side - I've also flushed the motor and am using Mobil 1 synthetic in her and I'm not sure if the frequency is related to those things or some underlying problem that is getting worse but I am now throwing these codes almost daily.
 
#19 ·
You need to get set up to read the computer and read the AVCS operating angle.
You can do this via FreeSSM (search over on subaruoutback.org)

CHECK CURRENT DATA.
1) Start the engine and let it idle.
2) Measure the AVCS system operating angle
and oil flow control solenoid valve duty output
using Subaru Select Monitor or general scan
tool.
NOTE:
• Subaru Select Monitor
For detailed operation procedures, refer to
“READ CURRENT DATA FOR ENGINE”. <Ref.
to EN(H6DO)(diag)-26, Subaru Select Monitor.>
• General scan tool
For detailed operation procedure, refer to the
general scan tool operation manual

Check:
Is the AVCS system operating
angle approx. 0 deg., and oil
flow control solenoid valve duty
output approx. 10%?

If Yes:
Check the following
item and repair
or replace if necessary.
• Oil pipe (clog)
• Oil flow control
solenoid
valve (clog or
dirt of oil routing,
setting of
spring, clog of
valve)
• Intake camshaft
(dirt, damage
of
camshaft)
• Timing chain
(matching of
timing mark)

If No:
A temporary malfunction.
Perform
the following, and
clean the oil routing.
Replace the
engine oil and idle
the engine for 5
minutes, and then
replace the oil filter
and engine oil.
 
#21 ·
Have fun! The next step after you get FreeSSM running will be RomRaider which will allow you to log the parameters, and you can 'catch' it while it happens. The folks over on subaruoutback.org are very helpful and should be able to help interpreter the log. Good luck!
 
#22 ·
Ok I got my cable and did some logging yesterday in RomRaider.

At idle I think my values are okay. As the engine speeds up you can see that they are angle and duty are no where near in sync as the Right Intake Angle pretty much stays at 0 while the Left fluctuates.

Does this log tell me anything or point me in a direction to a cure.

I presume Right side is Passenger side or Bank 1 per the P0011 error code?

(The error was thrown at in the last 2 minutes of the log but the readings appear to be consistent throughout the log)
 

Attachments

#24 ·
the outback forum was great.

Long story short when I went to swap the solenoid to see if the code followed the solenoid I discovered the solenoids were different. Turns out my brother's mechanic had put a the VVL solenoid that goes in the back of the passenger side. It's a 1/2" shorter and has completely different oil ports. So turns out there was no problem other than an incompetent mechanic!

Picked up a new (correct) valve and have been driving for 4 days now with no more codes!

for reference: http://www.subaruoutback.org/forums/109-gen-3-2005-2009/294313-advice-needed-h6-w-p0011-code-2.html
 
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