Subaru Outback Forums banner

1 - 14 of 14 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
:29:

Hello all, I have a 2008 Subaru Impreza Outback Sport AWD 2.5L SFI SOHC 4cyl

I am searching for a DYI service manual. I looked for a chiltons or haynes but no luck.

I received a P0028 code and the book refers to this as an Oil Intake Valve Solenoid.

The dealer told me it is called an "Oil Pressure Valve Solenoid". They priced it out at $139 and it looks easy to replace on bank 2, (the drivers side).

Does anyone know how to test this valve to see if it is actually malfunctioning?

Or could it be the Oil Pressure switch that works in conjunction with the Oil Pressure valve?

Does anyone know of a DYI service manual, eg. Chilton, Haynes?

Thanks and Regards.

osowskig
 

·
Registered
Joined
·
2,359 Posts
I recommend alldatadiy.com. You pay a yearly subscription but the information is equivalent to the Subaru FSM. Should contain a diagnostic procedure for that code.
 

·
Registered
Joined
·
16,289 Posts
The P0028 code is set when the pressure sensor switch condition (closed, open) does not correspond with the duty cycle signal that's being sent to the related solenoid.

The solenoid controls oil pressure to the variable valve lift cams while the pressure sensor checks to see if the pressure is, in fact, high when it should be high and low when it should be low.

The troubleshooting tree starts out by checking the wiring between the engine control module and the pressure sensor switch, rather the solenoid. Presumably the idea is to make sure that the pressure sensor function is okay, and after that, presume that the fault must be the solenoid.

There have been cases where the pressure sensor switch failed -- in some the sensor was (visibly) leaking and wouldn't respond properly to the actual oil pressure.

The solenoid, of course, could also fail to function properly; however, if there were an open or short in the solenoid or the wiring to it, that would generate a different trouble code.

This post (My 2007 Outback is leaking/Burning Oil - Subaru Outback - Subaru Outback Forums) has a good photo of the left bank solenoid (on a 45 degree angle) with the aqua/pale blue connector, and the pressure sensor vertical to the left of the solenoid with the white connector. (Read down for cautions when installing the switch, and to post #19 for another P0028 case caused by the pressure switch, not the solenoid.)
 

·
Registered
Joined
·
1,600 Posts
Got the same code shortly after an oil change. I was in a pinch and had to use a Walmart filter. Changed to a Purolator filter and cleared the code. Code has not returned. Maybe a fluke, maybe not. Just putting it out there incase others get the same.
 

·
Registered
Joined
·
49 Posts
Hi,

I have just started to explore the possibilities of romraider and freeSSM - what a revelation !

This issue can be monitored and logged very easily with romraider.

The ECU command for the inlet valve lift (solenoid) is "VVL Lift Mode (raw ecu value)" and the responses from the pressure sensors are "Engine Oil Pressure Switch #1 (On/Off)" and "Engine Oil Pressure Switch #2 (On/Off)".

When the command changes from 1 to 3 the pressure sensors should both go from 1 to 0. Do your log and you can trend the values either against time or any other parameter :).

It's a good start for further diagnosis.

Kind regards,

Tapani
 

·
Registered
Joined
·
16,966 Posts
Got the same code shortly after an oil change. I was in a pinch and had to use a Walmart filter. Changed to a Purolator filter and cleared the code. Code has not returned. Maybe a fluke, maybe not. Just putting it out there incase others get the same.
interesting! A co-worker reports that aftermarket filters are known to cause a similar problem in Mercedes-Benz's .
 

·
Registered
Joined
·
16,966 Posts
Hi,

I have just started to explore the possibilities of romraider and freeSSM - what a revelation !

This issue can be monitored and logged very easily with romraider.

The ECU command for the inlet valve lift (solenoid) is "VVL Lift Mode (raw ecu value)" and the responses from the pressure sensors are "Engine Oil Pressure Switch #1 (On/Off)" and "Engine Oil Pressure Switch #2 (On/Off)".

When the command changes from 1 to 3 the pressure sensors should both go from 1 to 0. Do your log and you can trend the values either against time or any other parameter :).

It's a good start for further diagnosis.

Kind regards,

Tapani

I hate buy another cable. Will SSM work with a Tactrix cable?
 

·
Registered
Joined
·
6 Posts
Discussion Starter #8
Hi,

I have just started to explore the possibilities of romraider and freeSSM - what a revelation !

This issue can be monitored and logged very easily with romraider.

The ECU command for the inlet valve lift (solenoid) is "VVL Lift Mode (raw ecu value)" and the responses from the pressure sensors are "Engine Oil Pressure Switch #1 (On/Off)" and "Engine Oil Pressure Switch #2 (On/Off)".

When the command changes from 1 to 3 the pressure sensors should both go from 1 to 0. Do your log and you can trend the values either against time or any other parameter :).

It's a good start for further diagnosis.

Kind regards,

Tapani
Hi Tapani,

May you please recommend a USB cable to work with the FreeSSM software and USB interface? I saw the VAG-COM recommended but strangely enough the Subaru is not listed as being supported. Maybe I have the wrong link. I do not know a lot about the ECU, do you know which type is in the Subaru?

Thanks and Regards,
 

·
Registered
Joined
·
2,359 Posts
Using FreeSSM in this case will not tell help you resolve this issue.

If the ECU commands pressure and the sensor does not detect pressure then you still don't know if the switch if bad or if the pressure sensor is bad.

The only way to resolve this without guessing is by hooking up a oil pressure gauge at the same location and measuring pressure when the ECU commands pressure.

If it was me, I would go with the one that more commonly fails which is probably the switch. I am not speaking from experience with this switch though. You could also probably take the switch off and test it.
 

·
Registered
Joined
·
16,289 Posts
That's right. The OBD has already determined that the pressure switch status isn't consistent with what the solenoid should be doing. That's about all FreeSSM and RomRaider Logger can do as well.

There are separate DTCs (diagnostic trouble codes) for a short or open circuit to the solenoid, which could cause it to malfunction, but there's no diagnostics to detect, for example, if the solenoid is mechanically stuck open or closed and not responding appropriately. The pressure switch will tell if the pressure is wrong, but not why. Moreover, if the pressure switch fails, there's no DTC for it, other than the one already indicated.

[http://www.subaruoutback.org/forums/66-problems-maintenance/35622-oil-pressure-sensor-switch-how-clicks.html might be of interest. Although it's about the engine oil pressure switch, they're pretty much the same as far as physical design and function.]

Check for signs of oil seepage around the pressure switch. This is usually an indication that the switch is failing, if not already inoperative.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #11
That's right. The OBD has already determined that the pressure switch status isn't consistent with what the solenoid should be doing. That's about all FreeSSM and RomRaider Logger can do as well.

There are separate DTCs (diagnostic trouble codes) for a short or open circuit to the solenoid, which could cause it to malfunction, but there's no diagnostics to detect, for example, if the solenoid is mechanically stuck open or closed and not responding appropriately. The pressure switch will tell if the pressure is wrong, but not why. Moreover, if the pressure switch fails, there's no DTC for it, other than the one already indicated.

[http://www.subaruoutback.org/forums/66-problems-maintenance/35622-oil-pressure-sensor-switch-how-clicks.html might be of interest. Although it's about the engine oil pressure switch, they're pretty much the same as far as physical design and function.]

Check for signs of oil seepage around the pressure switch. This is usually an indication that the switch is failing, if not already inoperative.
So if I pull the switch out, from what people are saying here, I can test it by plugging it in the connector and watching if it opens/closes. As for testing the solenoid, would that be somewhat the same test?

There is no leakage whatsoever, there are only 40,000 miles and there is not a spot of oil on the engine.

How convenient, the OBD code points to the most expensive part quoted @$145.00 where as the person above said to try the switch first, which is only @$8.00

The FreeSSM actually provides more troubleshooting information with the naming the switch as a possible contender as opposed to the OBD Code which points to the more expensive part in this case.

It could be that the meter does not read the ECU correctly, and possibly the FreeSSM is better suited for the job. That would be a point back to my above question as for what is the ID of the ECU so when looking for compatible meters how do you match it up? Thus, I purchase an Inovva 3150b and subaru is not even listed in the supported vehicles.
 

·
Registered
Joined
·
49 Posts
Yeah, my point was to log the values and see if the fault it's permanent.

Also, if you look at the AFR values under a WOT acceleration and if the inlet valves on the other bank won't open all the way I would assume it would have an effect. Further, you may compare your MAF curve to mine for example. -edit: Sorry, yours is a 2.5 - so not directly comparable.

Having the capability to log all data opens a lot of doors :)

Kind regards,

Tapani

PS I have the VAG cable and it works like a charm.
 

Attachments

·
Registered
Joined
·
16,289 Posts
So if I pull the switch out, from what people are saying here, I can test it by plugging it in the connector and watching if it opens/closes. As for testing the solenoid, would that be somewhat the same test?
No. The pressure switch cannot be checked that way. It switches in response to oil pressure applied to an opening in it's base. (See the thread I linked to in post #10.) You would have to know the pressure at which it is supposed to switch, and be able to apply that to the switch.

Do a search here, and on other Subaru forums, for P0028 -- it's not an uncommon trouble code and there are quite a few posts about it.

Edit: I checked the resistance of the pressure switches on my 07 with the engine off, and confirmed that the switches are closed, that is, there's low resistance to ground. But as noted in my linked thread, one failure mode for the engine oil pressure switch is that the internal contacts become corroded and don't make good contact. If that were the case with the VVL pressure switch, it would cause a CEL when the pressure was supposed to be low, because to the ECM the open circuit switch would appear as if the pressure is high. From this, I think that at least one test would be to measure the resistance across the switch with the engine off. (Remove the connector. There's a single small contact terminal inside. Measure between the terminal and a confirmed good ground.) The resistance should be near zero. If it's open circuit, or very high, the switch is bad.

I found the resistance of both switches to be around 10 Ohms. This seems high to me and might indicate that the contacts are starting to deteriorate. But I would have to check with a brand new one to be sure, because they might have a fixed resistance built in. If you do make the measurements, post the results here (or in my companion thread:http://www.subaruoutback.org/forums/66-problems-maintenance/49468-variable-valve-lift-oil-pressure-switch-resistance.html#post473452) for comparison.

Edit II: Been searching other Subaru forums and there's a fair number of posts about P0028 that turned out to be due to low oil, so when this (or the related P0026 code) shows up, check the oil level in the engine.
 
1 - 14 of 14 Posts
About this Discussion
13 Replies
7 Participants
Dale Duxbury
Subaru Outback Forums
Welcome to the Subaru Outback Owners Forum, we have tons of information about your Subaru Outback, from a Subaru Outback Wiki to customer reviews.
Full Forum Listing
Top