The Dreaded Subaru p0011 and p0021 DTC Codes, Don’t Let Them Wreck Your Turbo!

The right cylinder bank is fed before the left bank and from the same line, so we checked the right AVCS screen as well.  To get to it, we had to remove our large air inlet for our Cobb Tuning air box that we had fabricated to make room.  We think you might not have to do this if your car has a stock air intake or a rotated mount turbo.

Using the same technique to avoid taking the fitting off the fuel rail we remove the right banjo bolt.  The Screen was already removed here as well.  What now?

There is one more filter screen on this oil circuit.  The external line that feeds the AVCS sprockets feeds the turbo first!  Now we were wondering if this screen clogged up.  It would make sense if the screen started to clog, the last part to get oil, the left cylinder bank AVCS sprocket would stop working first, then as it got worse, the right bank would stop working.  The Precision Turbo has a ball-bearing center section that doesn’t require much oil flow, but even though it is fed from the oil galley first, it would have problems last.  This is how it went in our car.

So we had to check this last screen. It is found in the banjo bolt at the backside of the engine on the right side as shown here.

When we removed the bolt and took the fitting out of it, it was filled with a jelled oil glop.  What had happened is Christa only drives about 4 miles a day during the school week so her car never warms up fully until she drives on the weekends where she drives farther visiting friends.  Even though we use the best synthetic oil and change the oil every 3000 miles, the lack of heat allowed moisture and Ethanol residue from the E85 fuel to mix and form a jellied glop. This glop eventually clogged the turbo pre-filter and gradually cut off the oil supply to first the AVCS system then the turbo.

We checked our turbo and found it didn’t spin as freely as your typical ball bearing turbo and had some axial play in the shaft. For a ball bearing turbo, some radial play is acceptable but zero axial play is.  We sent the turbo back to Precision and sure enough, it was not ruined but needed a rebuild. Instead of rebuilding the turbo they are going to be sending a Second Generation improved version of this turbo for us to evaluate!

We will also be leaving the turbo pre-filter out of the Banjo fitting when we put it all back together as many Subaru tuners do.

Lessons learned?

  1. If your Subie WRX/STi throws a p0011 and or p0021 code, check your filter screens first to hopefully avoid turbo damage.
  2. If you spend a lot of time doing extremely short hop driving, your oil change intervals should probably be something like every 1500 miles, especially when running E85 which runs cooler and moister. An engine’s oil needs to get up to operating temperature to drive off water and the volatile parts of combustion residue of which E85 makes much more than gasoline.
  3. Doing some research on these common codes on NASIOC would have saved some grief as just a little digging showed that treating the issue as an electrical issue first has caused quite a few nuked turbos. I am notorious about hating forums, but NASIOC has good info and the Subaru online community isn’t as bad as many.

At least we are going to get to evaluate a new Gen II Precision direct factory replacement turbo in the process!  Stay tuned for that.



  1. Had this happen on the family Legacy GT while I was in college. I spent the better part of a month trying to figure this one out. I too thought it was an electrical problem and knew for a fact the TSB was done because my parents bought it new and did all the service at the local dealership. When I got around to looking at the turbo it was too late and we had to get a new one. My commute to campus was also only like 5 miles so I could thankfully catch a bus there while I tracked the problem down.

  2. Mike,
    You might run BG EPR through just before the next oil change and short cycle the oil change (500 mi) after that to clean out the oil passages. The 05-06 (BL/BP) Legacy had a bigger problem with the stock VF40 turbo because the turbine shaft had a very thin center. When the filter would clog the turbo would grenade and send shrapnel to the pan, contaminate the oil cooler and load up the filter until it went into bypass. Finally taking out the engine bearings. Many XTs and GTs met their demise this way. I bought my 05 GT with a new turbo bolted on. I replaced the oil cooler and banjo bolt with the unfiltered AVCS part, cleaned the pan and the oiling system components, as well as changed the oil at three 500 mile intervals with conventional oil (3k thereafter with synthetic). The EJ255 lasted another 60k until the bottom end became too noisy at 200k. It was a good excuse to rebuild it with EJ257 crank & rods, King bearings, and Mahle forged pistons and I rebuilt a VF52 for it

  3. The LH AVCS Filter is located on the front of the cylinder head behind the inner timing cover. You need to disassemble all the timing belt and LH Cam gears to gain access to it. Putting it on top would sure make it easier, but that’s why you didn’t find the filter.

    1. I am pretty sure thats what we got and its the same as pics from other people, the TSB, and youtube videos. When I take in the engine apart I will verify!

    2. See Hammerdown’s post on LegacyGT: this banjo bolt can be removed by filing the nub off the bolt and gently prying the timing cover.

  4. Mike , the banjo with the dimple is typically the one with the screen. Ryan is right about the driver’s side.

  5. This post is pretty old. Hoping someone can help me out. My wife’s 2011 Subaru Touring XT (turbo) is pulling those same codes. P0011 & 0021. Synthetic oil change done 3k miles ago, just did another one today just to be sure it’s clean. Mobile 1 – 5w-30 with top line oil filter.
    Car only has 59k miles. I am trying to find location of the banjo bolts. Only seeing pics & vids for 2010 and under. Anyone know the location? Thanks!!

    1. Might be too late, but banjo bolt one is behind timing cover on driver side. 2 is behind the block passenger side, and 3 is under the intake manifold passenger side. Gotta pull off a ton of stuff to get them all

    1. Shell Rotella T6 5W-40 is the go to oil for our cars. I switched from Mobil 5W-30 and I have noticed less oil loss between changes. Mobil oil is too thin and gets past the turbo seals and gets burned.

Leave a Reply

Your email address will not be published. Required fields are marked *