Subaru Error Code After Oil Change

I have a Subaru 2007 Impreza 2.5i, and recently took it to a "Quick lube" type of place for a cheap oil change.  The next day, The check engine light went on, accompanied by a blinking cruise control light.  I went to Winchester auto to get the error code read (they do it for free!), and it was throwing P0026 (P0026 - Intake Valve Control Solenoid Circuit Range/Performance (Bank 1)).  Basically something to do with the oil circulation system.  After some more reading, I found it could be caused by a number of things, such as a sub-par oil filter (installed by a corner cutting mechanic), or over filling the oil, or the actual intake valve part.

I checked the oil level, and it seemed a bit high, but not overly high.  I went and bought an oil filter, but the next start up showed the check engine light/blinking cruise control stopped flashing, and everything seemed to be back to normal.  This all happened yesterday (2/4/14), while the oil changed (and also power steering fluid flush) was done on 2/3/14.   Hopefully it stays off!  This experience makes me want to start doing my own oil changes again.

Update: 2/10/14

So there are two related codes, P0026, and P0028.  P0026 is related to the sensor bank on the passenger side, which is the error code I was getting (as mentioned above).  Searching the web on this code, I found some good sites.

  1. A good description of the problem, with pictures.
  2. An excellent explanation of how the oil pressure sensor switch works, with some forensics.
  3. A procedure of how to replace the oil pressure sensor switch.
  4. A list of possible causes for this code being thrown.

Today, I tried some troubleshooting steps.

  1. I measured the voltage at the connector to the oil pressure sensor switch (the white-capped item, see pictures in #1.)  It was 12 volts, which ruled out a problem with the connector.
  2. I measured the resistances in both the passenger (P0026 code) and driver side (P0028 code) sensor banks, from the terminal the sensor is a one terminal device) to ground.  The driver side was around 260 ohms, and the passenger side was around 40 ohms.  A brand new part for the sensor that is in the block (my sensors are in the head) measured about 1 ohm.
  3. Re-changed the oil, and put in a new oil filter.

Subsequently, as I was driving around to find the part for my car (a oil pressure sensor switch on the head, NOT the block - the sensor on the head was harder to find), the error code went off.  At this point, it looks like the problem was due to the oil change done previously.  They did appear to have over-filled it slightly, and maybe they forgot to replace the old filter.  The oil looked dirty, as well.  They might also have used the wrong oil weight (my car requires 5W-30 oil).  Of course, it is possible that they didn't do anything wrong, and these parts are on their way out, throwing an error code.  However, it is interesting that the code went off after repeating the oil change.  I will post an update if the code comes back on again.  I got a bad feeling from these mechanics, though, and I won't be going back to them.

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