P0446-Evap Emmis Control System

[OB99W]

On second thought, since Mike grounding B134 pin 10 set an additional code (P0443), it seems the ECU must be able to see something related to that pin. That also got me thinking about why P0446 is related to "vent control", but P0443 is a "purge control" code, and yet both are seemingly based on what's happening at the same ECU pin. I sometimes wonder if ECU programming is a bit "unscientific", especially when it comes to the DTCs. I've looked at Subaru info in addition to what Ferret provided, and the diagnostics for other models are basically the same, but sometimes given for code P0447, not P0446. There doesn't seem to be consistency in use of the codes for a particular fault. In fact, other manufacturers indicate that P0446 can be set due to lots of faults other than the condition we've been talking about.

 

Speaking of the PDF Ferret kindly made available, it seems to have (at least) two errors in it. The first is in part 10AJ3; once the harness has been unplugged, if checking for a short to ground, it would seem that "less than 10 ohms" shouldn't be the resistance that would indicate a problem. That would imply that measuring anything greater than 10 ohms would be acceptable (for example, 11 ohms), which of course it isn't. Obviously, the minimum resistance to ground of a disconnected wire should be quite high; Subaru probably meant 10 Mohms, not just 10 ohms. The other is in 10AJ4, where "Is the voltage less than 1 ohm?" should of course refer to resistance.

 

Things like these make me somewhat concerned about the diagnostic procedure using OBD-II codes in general. I suppose that's why at a certain point changing parts becomes a viable approach. As Nipper put it "sometimes you just have to swap them out and find out." Hopefully, you aren't paying dealer list price for the "privilege" .

[johnceggleston]

you all are amazing. your knowledge and patience are way beyond me. i'm just glad i don't have to deal with this problem.

 

i'll bet you can find a used ecu for 50$, maybe less. that seems way easiler. of course it's only easier if it works. do you know some one you could swap ecus with just to test it. it would be interesting to see if your ecu threw a code in some one else's car.

 

good luck.

[Mikevan10]

Thanks again for everyone's comments. I need all the support I can get! Here's how it all looks from here (in no particular order):

 

1. Is it really practical to repair an ECU without board level drawings, etc?

2. The scanner I am using does capture "freeze frame" data. Last I looked at it, it indicated that it picked up the "fault" right away because the coland temp was close to ambient. Idles speed, very low load, vehicle speed=0, etc. All stuff you would expect to see upon just starting the engine. I will write the exact info down and report back just in case it may reveal anything.

3. I will begin my search for a locally available ECU out of a junked vehicle today.

4. As far as "swapping them out", I am afraid that no one I know would want to risk it (assuming I knew someone who's car used the same ECU).

5. As far as the cost of trying to solve the problem by putting in a new ECU, I am afraid that this points to the unfortunate condition that most folks don't have the knowledge/interest in trying to find the root cause of problems like this. They take the car to the dealer who then shotguns in new parts until the problem goes away. Then he hands the poor slob owner a big fat bill. What's he to do? Oh yes, OBDII is such a wonderful thing (I read it in Endwrench - gotta be true).

 

More later

 

Thanks again all!

 

Mike V.

[nipper]

Thanks again for everyone's comments. I need all the support I can get! Here's how it all looks from here (in no particular order):

 

1. Is it really practical to repair an ECU without board level drawings, etc?

2. The scanner I am using does capture "freeze frame" data. Last I looked at it, it indicated that it picked up the "fault" right away because the coland temp was close to ambient. Idles speed, very low load, vehicle speed=0, etc. All stuff you would expect to see upon just starting the engine. I will write the exact info down and report back just in case it may reveal anything.

3. I will begin my search for a locally available ECU out of a junked vehicle today.

4. As far as "swapping them out", I am afraid that no one I know would want to risk it (assuming I knew someone who's car used the same ECU).

5. As far as the cost of trying to solve the problem by putting in a new ECU, I am afraid that this points to the unfortunate condition that most folks don't have the knowledge/interest in trying to find the root cause of problems like this. They take the car to the dealer who then shotguns in new parts until the problem goes away. Then he hands the poor slob owner a big fat bill. What's he to do? Oh yes, OBDII is such a wonderful thing (I read it in Endwrench - gotta be true).

 

More later

 

Thanks again all!

 

Mike V.

 

OBD II is much better then OBD I , or worse OBD none

 

I think we have taken you as far as we can, try one more thing. MAke sure there are no shorts/opens in the harmess itself, hook a meter up to the ends and wiggle the wire to make sure there is no broken wire. Confirm that, then it will be safe to plug in another ecu.

 

nipper

[OB99W]

you all are amazing. your knowledge and patience are way beyond me.[...]

Maybe ; in the long run we still get greasy hands, skinned knuckles, etc., at least on the jobs we're not just "consulting" on from a distance.

[johnceggleston]

this is just my observation, but based on the fact that some of the engines / trans are plug and play with the same ecu, there may be several from similar years and models that would work.

 

what do you think?

[Mikevan10]

johnceggleston said, "this is just my observation, but based on the fact that some of the engines".

 

I am not sure exactly what you mean, but if you are suggesting that Subaru used the same ECU in several models and/or years, that does not square with what I was told a few hours ago. I ran over to a local job that specializes in Subaru repairs. They also have a Subaru salvage yard of sorts and they sell used Soobies. I asked them if they had an ECU for a 1997 Legacy, 2.2, California car. The guy referred to some documentation and then told me I needed to get the numbers off of my ECU since they used more than one version in vehicles meeting my description!

[johnceggleston]

you are right, according to car-part.com they were 6 used in 2.2L lagacys in 97, two of the 6 are designated as "calif".

 

most dealers and shops only go by matching part numbers, they would say you can't put a 2.2 engine in an outbach. but you can. they would say you can't put a 96 leg a/t in a 95, but you can. i was just wondering if any one knew any swapability for ecu's. but unless you're going to a local parts yard that will let you bring it back if it doesn't work, there's no reason taking a chance. get the exact match.

 

car-part.com prices vary from 50$ to 150$. you will need your part number when you search, something like "22600 a020". i can't remember exactly.

 

good luck.

john

 

johnceggleston said, "this is just my observation, but based on the fact that some of the engines".

 

I am not sure exactly what you mean, but if you are suggesting that Subaru used the same ECU in several models and/or years, that does not square with what I was told a few hours ago. I ran over to a local job that specializes in Subaru repairs. They also have a Subaru salvage yard of sorts and they sell used Soobies. I asked them if they had an ECU for a 1997 Legacy, 2.2, California car. The guy referred to some documentation and then told me I needed to get the numbers off of my ECU since they used more than one version in vehicles meeting my description!

[Cougar]

Mike, if you can get a used ECU for around $50 dollars it would be a good deal. If you have to spend more than $100 dollars for one then you might want to at least consider looking at the inside of yours just to see if it a bad connection and save yourself some cash.

 

I like to tinker around on things like this so I would have no problem opening it up to see what was causing the trouble. Even without a diagram it is pretty easy to follow the connections.

[Mikevan10]

OK, I'm back (sorry).

 

Since we last spoke, I have learned that the particular "model" (i.d. number) of ECU that is in my car (AD050 in case anyone's interested) was ONLY used on 1997 2.2 Legacys with manual trans and that were California spec!. That really bites since it severely limits the availability of used examples of this part. This kind of practice unnerves me. Anyway, I could not find one locally so I went ahead and mail ordered one from so no name junk yard in Jersey. Should be less than 60 bucks with shipping so I figured I roll the dice. New ones are on the high side of $500.00 and I don't even know 100% sure that I need one!

 

Here's some more new info that may be interesting:

My wife drove the car about 100 miles, round trip, last night. This included highway and city driving. When she left there were several OBDII parameters that were "not ready/incomplete" since I had cleared codes recently. Well, when she returned last night I ran out with the trusty Actron CP9145 scanner and read the codes. The "good" news is that there is still only one fault code (P0446 of course) but the troubling news is that there are still two parameters that are coming up incomplete when you do a I/M Readiness check. These are "Catalyst" and "EVAP Sys". Everything else shows ok or N/A (and some of these did show "inc" prior to the drive).

 

What say you now?

 

Thanks for your time and consideration.

 

Mike V

[nipper]

OK, I'm back (sorry).

 

Since we last spoke, I have learned that the particular "model" (i.d. number) of ECU that is in my car (AD050 in case anyone's interested) was ONLY used on 1997 2.2 Legacys with manual trans and that were California spec!. That really bites since it severely limits the availability of used examples of this part. This kind of practice unnerves me. Anyway, I could not find one locally so I went ahead and mail ordered one from so no name junk yard in Jersey. Should be less than 60 bucks with shipping so I figured I roll the dice. New ones are on the high side of $500.00 and I don't even know 100% sure that I need one!

 

Here's some more new info that may be interesting:

My wife drove the car about 100 miles, round trip, last night. This included highway and city driving. When she left there were several OBDII parameters that were "not ready/incomplete" since I had cleared codes recently. Well, when she returned last night I ran out with the trusty Actron CP9145 scanner and read the codes. The "good" news is that there is still only one fault code (P0446 of course) but the troubling news is that there are still two parameters that are coming up incomplete when you do a I/M Readiness check. These are "Catalyst" and "EVAP Sys". Everything else shows ok or N/A (and some of these did show "inc" prior to the drive).

 

What say you now?

 

Thanks for your time and consideration.

 

Mike V

 

catlayst is a tired o2 sensor, if that is a truthful reading.

 

Get a new ECU then check.

 

nipper

[OB99W]

[...]Here's some more new info that may be interesting:

My wife drove the car about 100 miles, round trip, last night. This included highway and city driving. When she left there were several OBDII parameters that were "not ready/incomplete" since I had cleared codes recently. Well, when she returned last night I ran out with the trusty Actron CP9145 scanner and read the codes. The "good" news is that there is still only one fault code (P0446 of course) but the troubling news is that there are still two parameters that are coming up incomplete when you do a I/M Readiness check. These are "Catalyst" and "EVAP Sys". Everything else shows ok or N/A (and some of these did show "inc" prior to the drive).

 

What say you now?

The two monitors that haven't "set" yet (Catalyst and EVAP) are typically the ones that have the more stringent criteria. Many of the monitors will set within one drive cycle, but those two may take a few before all the requirements are "hit" during a drive. The EVAP may or may not relate to the P0446 you're seeing, but I suspect that you still have only the problem causing that code.

[nipper]

have you tried swapping this valve with one from a donar car? maybe there is something odd in the valve that we arent seeing or cant see without a scope (like sluggish response)

 

nipper

[Mikevan10]

I have not tried swapping out the valve lately. But this code first appeared about two years ago and I replaced the vent/purge valve at that time to no avail. Code has existed since then.

 

So the fact that the monitors have not "set" in now well over 100miles of driving in various conditions is normal? Really makes getting a car through inspection a challenge doesn't it?

 

Mike V

[OB99W]

[...]So the fact that the monitors have not "set" in now well over 100miles of driving in various conditions is normal?

Hmmm, I meant to say "set completed/ready"; yours seem to remain stubbornly "incomplete/not ready". If you're putting miles on during which the drive cycle requirements are being met (sufficient engine warmup, road speed, time at that speed, brake usage, time not run, etc.), then this may be indicative of more problems.

 

Even if codes other than P0446 aren't being stored, it still might be worthwhile to look at data from things like the O2 sensors. Did you get a chance to make note of the freeze frame data for the P0446 code?

[Mikevan10]

Sorry for the delay (I know you guys are on the edges of your seats), but here is some freeze frame data:

 

TROUBLE CODE P0446

ENGINE RPM 800

CALC LOAD 5.1%

MAP 9.7" Hg

COOLANT 138 F

LT FTRM1 2.3%

ST FTRM1 0.0%

VEH SPEED 0 MPH

FUEL SYS 1 OPEN

FUEL SYS 2 N/A

 

That's it.

 

Drove the car on another 100 plus mile trip, which again included highway cruising and city driving. OBDII I/M readiness check still says

"Not all supported on-board readiness codes are complete"! And it goes on to show "Catlyst Mon" and "Evap System Mon" as "inc". Everthing else shows as ok or N/A. There is now well over 200 miles on the car and many engine starts since the codes were cleared and it still is not ready??? I cannot believe this is normal, expectable or even tolerable. This is supposed to be a "READINESS" test, not a pass/fail test so even if my catalyst system, for example, was malfunctioning, I would expect OBDII to say the test was complete even though it may give me a DTC. Right???

[nipper]

Sorry for the delay (I know you guys are on the edges of your seats), but here is some freeze frame data:

 

TROUBLE CODE P0446

ENGINE RPM 800

CALC LOAD 5.1%

MAP 9.7" Hg

COOLANT 138 F

LT FTRM1 2.3%

ST FTRM1 0.0%

VEH SPEED 0 MPH

FUEL SYS 1 OPEN

FUEL SYS 2 N/A

 

That's it.

 

Drove the car on another 100 plus mile trip, which again included highway cruising and city driving. OBDII I/M readiness check still says

"Not all supported on-board readiness codes are complete"! And it goes on to show "Catlyst Mon" and "Evap System Mon" as "inc". Everthing else shows as ok or N/A. There is now well over 200 miles on the car and many engine starts since the codes were cleared and it still is not ready??? I cannot believe this is normal, expectable or even tolerable. This is supposed to be a "READINESS" test, not a pass/fail test so even if my catalyst system, for example, was malfunctioning, I would expect OBDII to say the test was complete even though it may give me a DTC. Right???

 

can you do this again when the car is warmed up?

 

The problem may be your scanner. Not all scanners can read subarus, as (subaru being subaru) has a code on to itself, that meets the letter of the law, and can be read by most scanners. Ford also does the same thing.

WHne i fisr installed my scantool, i got the same thing, untill i told it i was running it on a subaru, then it was happy.

 

nipper

[Mikevan10]

Hi Nipper,

 

1. I will review the instructions for the scan tool and see if they say anything specific about Subarus. Is that what you are saying? That I may find instructions there about how to deal with a Subaru?

 

2. As far as recording freeze frame data after the car is warmed up, I believe the only way to do that would be for me to first warm the engine up, then clear the codes, then start the engine twice. The CEL will come back on at that point and new freeze frame data will be recorded. At least, that is how I understand it. Now, I could do that but then I would be starting from scratch trying to get to a point where the OBDII says it is "Ready" for I/M. Not sure I want to do that.

 

Thanks again,

Mike

[nipper]

You cant clear the codes using the reader? its just that im seeing nymbers that are higher then on my car. One is the load, even cold my car runs at 3% 5% with the ac on.

 

nipper

[OB99W]

Readiness is dependent on particular drive cycle requirements being met. Assuming that the car has been driven sufficiently to have met the requirements (and that would probably be the case by now), then it would appear that at least one parameter for both the Catalyst and Evap Sytem monitors is not meeting what the ECU expects to see, or the ECU is misreading a sensor, etc.

 

For example, if the ECU saw the engine temp as being too low, it would keep operation "open loop", and even if all the other parameters met a drive cycle requirement, the report would still be "incomplete". I'm not saying that's actually what's happening -- the long term fuel trim, being only a few percent positive (I didn't see a "-" sign in the data), indicates a slight increase of the injector "on" duty cycle that typically would be offsetting a somewhat lean average condition. That wouldn't be what's expected if running open loop longer than usual.

 

As Nipper suggested, fully warming the engine, clearing codes, and then seeing what "freezes" when the P0446 is set might be interesting. By the way, engine load is calculated by dividing airflow by peak airflow; bad sensor data, vacuum leaks, or true loads on the engine (even a battery that's down and has the alternator working harder than usual) can cause the load percentage to go one way or the other from "normal".

[nipper]

My car

138 degrees

800 rpm

MAP 4.1

Load 3%

 

i think we may be on to something. Could there be a cracked/leaking/broken line in the EVAP system?

 

nipper

[OB99W]

If anyone hasn't seen them already, the following links might prove interesting. I think they provide some insight into the complexities of OBD-II, readiness, and what sort of things can cause strange behavior.

 

http://endwrench.com/images/pdfs/OBDEWWin05.pdf , page 20 in particular.

 

http://www.autocenter.weber.edu/OBD-CH/presentations/Moye-VT.pdf

 

PA inspection specifics, including that 1996-2000 models can have two readiness monitors incomplete and still continue with inspection:

http://www.drivecleanpa.state.pa.us/drivecleanpa/service/IM_update_v5n2.pdf

 

Inspection flow chart, detailing procedure if there's a readiness problem:

http://www.drivecleanpa.state.pa.us/drivecleanpa/service/obd2flowcharts.pdf

[BigMattyD]

Mike: I have a thought... Look at the diagnostic procedure in the FSM scan I sent you. On section 10AJ2, step 6, it asks you to measure the resistance between terminals 1 and 2 of the solenoid. If it is shorted, (less than 1 ohm) you are to replace the solenoid AND the ECU. Having a short in that circuit must damage the ECU, probably a transistor or other component that actually does the switching. (Is that a poor design?)

 

Here is my thinking. You said that the CEL has been on for a long time, and that you had this same code 2 years ago, and replaced the valve, but the CEL stayed on. It is my theory that the original valve was shorted, and you replaced it with a good part, but the damage had already been done to the ECM. Of course, because the CEL stayed on, you were not sure if it was because the repair you did was incomplete, or if there were other issues causing the CEL.

 

Now 2 years have gone by, you read the codes, and find several, but one of them is the same as you had back then, and it's the only one that returns when you clear the codes. You do all the diagnostics, but you come up with no good answers. The new solenoid reads 28 ohms, because it is the new one, and it hasn't been operating for two years, so it is like new. The connections are good, and the valve operates when you test it... confusing the issue.

 

So get a new or used ECU if you can. I think there is enough reason to suspect it is damaged. If you have the ability, maybe you could take it apart and replace a faulty component. Or maybe Cougar could start a side business fixing these things....

 

Matt D.

[nipper]

If anyone hasn't seen them already, the following links might prove interesting. I think they provide some insight into the complexities of OBD-II, readiness, and what sort of things can cause strange behavior.

 

http://endwrench.com/images/pdfs/OBDEWWin05.pdf , page 20 in particular.

 

http://www.autocenter.weber.edu/OBD-CH/presentations/Moye-VT.pdf

 

PA inspection specifics, including that 1996-2000 models can have two readiness monitors incomplete and still continue with inspection:

http://www.drivecleanpa.state.pa.us/drivecleanpa/service/IM_update_v5n2.pdf

 

Inspection flow chart, detailing procedure if there's a readiness problem:

http://www.drivecleanpa.state.pa.us/drivecleanpa/service/obd2flowcharts.pdf

 

like i said, the car wasnt warmed up yet.

 

good info

 

nipper

[Mikevan10]

Guys - I think I have found the problem (at least the one causing the P0446 DTC)!! I will get back to you with details later. Sincere thanks to all who took the time to think about this and offer there well considered advice and comments. Although it looks like it was a dumb mistake on my part that caused the lengthy struggle, I have learned alot in the process....

 

I'll get back to ya.

 

Mike V.