I am getting the P0026 code, when I checked the resistance on the switch, the multimeter was reading 29.8.

 

Also getting P0026 code



Our car was showing P0026 and we were experiencing a slow idle speed. The RPM would drop when stationary almost to the point of stalling. The code went away on its own for about a month and a half, but the idle issue remains intermittently.

The CEL came on again yesterday - I assume it is P0026 again but will have to confirm. I'll check the resistance if you can give me some more guidance. I have a multimeter, but have never tried to use it to diagnose an auto electrical issue.

 

Perhaps if you could provide some idea of how you have used the multi-meter in the past it could help focus the guidance we provide. Nevertheless, in the meantime, here's an outline:

Your multi-meter will have one or more resistance (Ohm) ranges. It's preferable if the multi-meter is a digital type, and not the analog that has a moving pointer. The latter can work, but some don't have a resistance range that will read out low resistance with good reliability. You want to choose a range that will show resistance between close to zero and, say, 200 Ohms.

The P0026 is related to the right (passenger) side VVL system. The oil pressure switch of concern is the one shown in the third photo in post #1 above. It's the part with the white connector. This is at the upper back of the right side head.

Remove the white connector. (Might have to work your hand in from the back, under the air duct.). When the connector is off, the black plastic top of the switch connector should be visible. (See the middle photo showing the left side switch.) Inside there's a single, thin, metal terminal.

Connect the negative (black) test lead of the meter to a good engine ground. Test the ground by touching the other (red) test lead probe to another spot on the engine. The meter should read less than 1 Ohm if the connections are good. Then move the red test lead probe to the switch terminal. The meter should now indicate the resistance of the switch. (Repeat the last two tests to be sure the readings are reliable.)

Because your symptom appears to be intermittent, it's possible that measuring the resistance in this way might not be conclusive. The reading might be low at this particular time, as would be expected with a good switch. But if it reads very high, I would think that is a positive test.

You can also pull the white connector on the left side (near the front of the head), and measure the resistance of the other switch, using the same technique. This would provide a comparison, which might be indicative.

It should be noted that the code along with poor idling could also be due to a malfunctioning VVL solenoid valve.

 

Resistance measured at oil pressure switches

plain OM, thanks for your very detailed instructions. I was able to measure the resistance at each switch.

Driver side: 13.3 ohms
Passenger side 40.7 ohms.

The passenger side has been giving me issues (code P0026). This was all read without the car running. Obviously there is a discrepancy there, but not sure how telling that is.

I suppose there would not be any value to doing something similar with the engine running?

 

Diagnostics steps from service manual (EN-91)

I also wondered if you've run through this diagnostic from the service manual, or if you think it would be valuable?

 

I did look at that diagnostic tree, but noticed that nowhere does it check the oil pressure switch condition. Yet the switch is critical to the way the engine control module verifies if the hydraulic pressure to the valve lift cams is correct. However, if you want, you could go through the sequence, although I suspect the suggested measurements will be fine.

If you have the full service manual, look at the engine General Description section. There's a section for the diagnostic codes (starts on page GD(H4SO)-8). In this section there's details of what criteria are used to generate a code. This is where the function of the oil pressure switch is described, and how its position -- on or off -- leads to a code.

There's not much more you can do with the engine running unless you have a scanner that can display the state of the VVL oil pressure switches. If you do, then with the engine idling, both switches should be closed, or "on". But I suspect that when the code is set (CEL on), the high resistance across the switch (~40 Ohms) will be read as "off".

In this regard, when the engine is off or at lower engine speeds, the oil pressure to the variable lift cam is low. It's only when the engine gets up to cruising-type speeds (and depending on some other factors) that the engine control module will command a switch from the low lift cam to the high lift cam. This is effected by changing the signal to the switching solenoid from a low duty cycle to a high duty cycle. More oil pressure is routed to the cams. The oil pressure switch, which is normally closed (there's continuity across it) when the pressure is low, will then go open. But I believe that's the problem with your passenger side switch - the resistance across the switch contacts is already too high -- e.g. your measured 40 Ohms -- and read by the ECM as "off". This is inconsistent for the diagnostic system; the ECM is commanding a "low", yet the switch, showing high resistance, is indicating a "high". This is not correct and that, I believe, triggers the code. [This is still a hypothesis, yet to be verified by experiences reported here.]

The fact that your code is for the passenger side, and your driver side switch is still down at around 13 Ohms (and no code), seems consistent with what I expected. The measurements start to provide a range -- 13 Ohms is still good, but 40 is going to be problematic.

I recently re-checked the two VVL oil pressure switches on my 07 and they hadn't changed -- still around 10 Ohms.

Thanks for the data; adding to the knowledge base.

If you decide to replace the switch yourself, be very careful not to over-tighten. There have been instances where the block, in the area of the switch, cracked. There's not much "body" around the threaded hole for the switch. (Not meaning to discourage you with this, but here's one example: http://www.subaruoutback.org/forums/66-problems-maintenance/45237-just-messed-up-big-crap.html)

p.s. If you do have the switch replaced, measure the resistance of the new one. Again, this would provide a reference for what it should/could be.

 

p.s. If you do have the switch replaced, measure the resistance of the new one. Again, this would provide a reference for what it should/could be.

Just purchased new one for my 2006 Tribeca - it's 4.7 Ohms

 

Very detailed reply - thanks! My inclination was to swap the right hand and left hand switches to see if eventually it returned the P0028 code. I assume they are interchangeable. However, reading that horror story definitely has me concerned! I'll have to read up more on the procedure and see if I feel comfortable doing that work. My mechanical skills are pretty modest.

 

Thanks gotwww. That's what I would expect, or even lower.

Were you getting one of the two trouble codes? How high is the resistance of the old switch?

 

Actually, I was getting P0028 (driver's side) and the resistance on that was all over the place (not consistent) but when I went to replace it this morning I saw what looked like water in the connector base that I think may have been causing it. I blew the water out and so far no codes.

 

Please let us know if it holds, or if you end up replacing, and if you do, and have the change, the resistance readings. ("All over the place" is a valid reading for this purpose!)

 

P0028

. on my 2009 Forrester,
P0028 (comes and goes, all around town driving though, seldom highway speeds)
left /driver side ~150 ohms (give or take, can;t remember exactly)
right/passenger side ~15 ohms (started on 20 then settled at 15)

seems consistent with what you are saying, huh?
having trouble finding part numbers though, ideas? parts diagrams available?

 

. on my 2009 Forrester,
P0028 (comes and goes, all around town driving though, seldom highway speeds)
left /driver side ~150 ohms (give or take, can;t remember exactly)
right/passenger side ~15 ohms (started on 20 then settled at 15)

seems consistent with what you are saying, huh?
having trouble finding part numbers though, ideas? parts diagrams available?

http://www.subarupartsforyou.com/cp_partdetail.php?partid=20385
p/n 25240AA060

Should be the same for the VVL oil pressure switch at the back of the right (passenger) side head.

 

both switches replaced

I ended up replacing one of the pressure switches in August. Was getting P0028 (driver's side). Measuring the old one I found that when the switch should have been closed the resistance was low, but not zero, but the longer I held the OHM meter on it the higher it went but it never stabilized out. This stopped the P0028 and it never came back.

Two weeks ago I started getting P0026 (passenger side) and since I had already had to replace one I figured for $12 ( Amazon.com: Beck Arnley 201-1954 Oil Pressure Switch with Light: Automotive ) it was worth replasing the second one also. Again, solved the problem completely. The second one measured 112 ohms when supposed to be closed.

2006 Tribeca 3.0L 170k

 

thanks, any reason to replace the passenger side unit at the same time if the reading is 15-20 (and there is no P0026 error) do you think?
***edit** just saw gotwww's post, I may just go ahead and replace both. I saw one comment about cheap oil filter causing these errors, maybe the filter/dirty oil affects the oil switch?
I sure hope this fixes the problem, cause the solenoid bolt on the left/driver side is blocked in by the timing belt cover.
Did I understand correctly that P0028 is left/driver side and P0026 is right/passenger side?

 

From the reports above, 15-20 Ohms doesn't seem to be problematic if it's stable and repeatable. However, if it's higher, or unstable, then if it isn't causing problems now, I suspect it probably will sooner rather than later.

P0026 is right side, P0028 is left side.

Please be careful when changing the sensor -- see the "Just messed up . . ." thread (linked) in post #7 above.

And, let us know how it works out.

 

installed the new Beck/Arnley sensor on driver side, P0028,
cel has not come back,
gas mileage has improved back to 20/28 or so
bad sensor once removed read 20 ohms
then after I blew the oil out it didn't register at all.

If I get around to replacing the passenger side I will take a new reading on both installed.

 

Thanks for the update. It's adding relevant information about these switches and the trouble codes.

Be interested in how the other sensor works out, and the readings on the new ones after installation.

Thanks again.

 

repeated VVL oil pressure switch failure

plain OM I have a 06 Sub impreza OBS, I've owned the car for 3.5 years and have replaced the VVL oil pressure switch 4 times now (always the left one) and it needs to be replaced again!

What happens is the CEL comes on (throws P0028) and the car runs a little rough, I notice oil drops on the garage floor, and when I check the white switch itself, it's all covered with oil.

My mechanic wants to try using a Subaru Genuine part this time. I am wondering if we should be looking for the cause of this parts failure. You seem to know a lot about this little part, any thoughts?

Should I have him replace the valve itself too?

Thanks for any input you might have!

 

Strange that the replacement switches should fail (leak) repeatedly. Are you sure the oil is coming from the switch itself, that is, from above where it screws into the head, and runs down from there?

If the replacements have all been aftermarket switches, and especially the same make, then there could be a problem with them. I'd certainly go with the Subaru part this time.

I don't see why the solenoid valve should be replaced if it's not malfunctioning.

The oil pressure switch is a fairly simple device. This thread (http://www.subaruoutback.org/forums...forums/66-problems-maintenance/35622-oil-pressure-sensor-switch-how-clicks.html) shows how they're built inside, and how they might fail. (The VVL switch is configured differently, for example, it has a different connector, but the basic idea of how they work is much the same.)

 

Thanks for the input....that's what I'm going to do, have the part replaced with a genuine Subaru part and see if that does the trick. I'll post back later.

 

got the P0026 last week, but only when powering up mountains on i-70 heading across Colorado, will be testing resistances tonight after work. are there other symptoms of pre-failure? like, one said MPG was better after replacing, any acceleration difference?

I've only had my '06 Outback H6 for about 5K miles, but something I've found odd is a sudden massive boost in power at higher (3500-ish) RPMs while accelerating. reminds me of the weak 1.6L and smaller cars I've owned when I'd turn the A/C off while trying to reach highway speeds, but a LOT stronger. is that normal for the VVL, or a symptom of an imminent failure? I've also experienced some intermittent and annoying power lag when accelerating from a stop, like floor it, it struggles (not hesitates or rough, just no real power) for about 20 ft then it screams to life.

 

getting about 8.5 ohms on both sides

 

getting about 8.5 ohms on both sides

Based on the earlier reports here, 8.5 Ohms doesn't seem bad for the oil pressure sensing switch in the VVL system provided it's consistent.

(On the H6, the VVL oil switching solenoid and the related "variable valve lift diagnosis oil
pressure switch" are both at the rear of the heads, whereas in the H4, the left side solenoid and switch are at the front. Also, be sure you're measuring the switches, not the solenoids.)

The FSM diagnostic procedure for codes P0026 or P0028 (H4 version shown in post #6 above) focuses on the solenoid. In fact, the FSM associates the codes only to a faulty solenoid, not to the pressure switch, even though it's become apparent that a faulty switch could also cause them. As noted earlier, the code is triggered when the oil pressure sensed by the switch doesn't correspond to what it should be (high, or low). This could also be due to a faulty solenoid, or to a problem with oil flow such that the pressure at the switch isn't correct.

 

hm, I may have tested the solenoid then. will give it another shot.

any thoughts on the acceleration? is that sudden power boost normal or a symptom of a problem with the VVL system?

 

I've heard a number of people describe the 3.0R output in similar terms. I've driven the older D model and I noticed it had a big surge as well.

You might be experiencing normal conditions.

 

My 10 Forester had P0026/P0028 code since 2011 but only intermittently during very hot summer times. The codes would come and go and occasionally stalled the engine. Subaru service could not figure out why and replaced ignition coil, spark plugs and catalytic converter in 2011. But problem remained until I moved to another state with cooler summer.

Two weeks ago, the P0026 came back again but did not stall the engine. I measured the resistance as suggested by this thread. Passenger side was 44ohms and driver side 22ohms. It seems like 22-25ohms is the cut off threshold to trigger the CEL. This morning I replaced both switches with OEM parts off Ebay. Those two faulty ones were both around 22ohms this morning when temperature was at 70s. I do not know why they are affected by temperature this much.

 

That's interesting. Hope you will let us know if the problem no longer appears with the new sensors. (Guess you will need a few days and conditions that, in the past, would have caused the fault to trigger.)

If replacing the sensors has solved the problem, it would tend to confirm that the high resistance (e.g., 22 Ohms) seems to be a good indicator of a fault in the sensor.

 

First off, I just want to say to plain OM, you are the man. Your write up of this problem is excellent and very clear. You probably saved me hours of work.

My buddy with an 06 Impreza Outback came by with a P0028 (which is left/drivers side) a week ago. I found this thread online and proceeded to test his car using the tests that plain OM described and referencing the results against what I saw here. What I found is a little unclear and unusual, but I felt I should post it here for you to interpret and possibly benefit.

First unusual thing: Testing the resistance of the switch's with the ignition key on (engine off) seemed to make a massive difference between testing them with the ignition key off. I could not work out how that could make any difference, but it did. Results:
Left (drivers side) switch - Key on: 28.6ohm Key off: 4.3ohm
Right (passenger side) switch - Key on:46.2ohm Key off:8.9ohm

This struck me as very odd. Why would the ignition being on effect the resistance of the switches? Some backround info - the multimeter is a Craftsman brand true RMS digital meter. I have had no previous problems with the meter, and I zeroed the leads multiple times. I performed the tests on the switches multiple times to make sure I didn't screw up the test, and got consistent results each time.

I called the Subaru dealer and found that they had new switches in stock, and they were only $16 each. So, being as they were so cheap, my friend elected to just replace both even though my diagnosis was inconclusive. Once I took the old switches out of the engine and had them on the bench, I tried measuring the resistance again and got the same results as I had with them in the car with the ignition key off (L - 4.3ohm, R - 8.9ohm). The new switches both tested exactly 1.3ohms on the bench. I have to admit that I failed to test them again once I had installed them in the car. I should have done that to see if the ignition being on affected the new switches as well. Oops.

Anyway, it's been a week and the problem has not returned. However, there is one more slightly unusual part to this story that may be important. After I had finished the repair, my friend casually mentioned that on the drive down to my house, his oil pressure light had flickered a few times when he went around some hard corners. I checked and topped off the engine oil... I had to add ALMOST 3.5 QUARTS of oil to his car. I didn't think about it too much at the time, but afterwords the thought occured that the momentary loss of engine oil pressure might have triggered the P0028 code. My friend is a, let's say "enthusiastic driver", so he might have been cornering with the engine RPMs high enough that when oil pressure was lost, the variable lift control solenoid was engaged, and high oil pressure should have been changing the timing.

I hope this information may help. I will try to keep an eye on this thread if anyone has any questions. Cheers.

 

Interesting.

The resistance reading should be made with the harness disconnected from the oil pressure switch, and then testing at the switch's connector contact. If you had the harness connected and were back-probing the connector to make the measurements, the readings could be skewed by the ECM circuit that's connected to the switch.

(When measuring resistance, the meter uses it's internal battery to effectively provide a known, fixed voltage to the item under test. It then measures the current flowing through the item, and displays the equivalent resistance. But with the key at ON, the voltage from the ECU is also being applied to the switch and therefore to the meter, and that is throwing off it's reading. Resistance measurements should only be made when there is no voltage in the circuit under test, and preferably when the item being tested is not connected to anything else.)

At 3.5 quarts low, I'm surprised that the engine wasn't unusually noisy and even survived. There's only about 4 quarts in the engine to begin with (if it's the 2.5 liter non-turbo engine.) But, yes, if the oil pressure drops when the switch is supposed to be closed, and it therefore opens, that could cause the DTC to be set.