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Subaru Legacy/Outback "Check Engine" Light Problems



  • Mine is a 2006 GT-Turbo with 5sp Manual. I ONLY get the CEL when I travel between my two homes. One home is at 7000' in a cold climate and the other is at about 3000' in the desert. Usually, I get the light when I go from the cold to hot climates. Every time I take it to the dealer, I'm told its a loose gas-cap.

    I NEVER fail to tighten the gas-cap and I am especially aware of that now. I suspect that the problem is caused either by the change in temperature or the change in altitude (pressure). I always buy gas at the half-way point between the two homes.

    I had a Forester with the same problem and then I had a Baja that never flashed a CEL.... ever.

    Comments? Ideas?
  • I have a 1996 Subaru Legacy Wagon. I bought it from a private party when it had 11,000 miles on it. Not long after I bought it, the check engine light came on. Twice when this happened took to the dealer, they said nothing was wrong turned it off. They never said it was a known problem. Living in Oregon, it was not a problem as there were no emission problems. Now in California, just the fact that the light is seen as on manually, they fail your smog. No emission problems, car problems of any kind. The print out mentions a Knock Sensor. Had it replaced, drove it about 100 miles, had it smogged, now the light is on again. I have two years to do something about this. I love the car, but the only alternative is to sell for scrap in two years. This just not seem right that you would be forced to junk a car that has an engine that is so quite when idling, you can't tell it is on, no emissions, etc.

    Would Subaru have a fix for this? One mechanic said it needs a new computer, about $1500. Another said it has nothing to do with the computer or catalytic converter. Any ideas?
  • xwesxxwesx Fairbanks, AlaskaPosts: 11,158
    Not that this is a solution, but you should seriously consider purchasing a scanner for the car. That way, when the light illuminates, you can read out and reset the codes yourself. This does two things: 1, you know what codes are tripping and how often, and 2, if something else goes wrong, you will not be in the dark about it (once the light is on, an infinite number of additional codes could crop up and you would have no idea).

    Also, it would alleviate the issue of occasional codes causing a fail when having the test performed.
    2014 Audi Q7 TDI, 2008 and 2013 Subaru Forester(s), 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup
  • So how does one buy a scanner and where do you get them? What do you look for? Also, is this in keeping with regulations to reset the codes prior to getting it smogged? Just wondering.
  • xwesxxwesx Fairbanks, AlaskaPosts: 11,158
    Scanners can be purchased at many, if not all, automotive parts stores, as well as online through many venues such as Northern Tools,, etc. They tend to cost around $130-$150, and you want a scanner that is OBD-II with CAN compliance.

    I am not aware of regulations related to resetting codes prior to getting an emissions test, but it is your car. As far as I am concerned, if the codes had an effect on the emissions coming out of the tailpipe, the car would not pass the test anyway and then you would have a legitimate reason to pursue repair. If it passes, the code was irrelevant. If the state has a problem with that, they are welcome to provide me with a car (and therefore have a say in its ownership) or kiss my.... cheek. ;)
    2014 Audi Q7 TDI, 2008 and 2013 Subaru Forester(s), 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup
  • ateixeiraateixeira Posts: 72,587
    I got an Actron for $99. Make sure it can read and reset codes also.
  • I usually go to my local O'Reilly's and use thier scan tool for free! Hope this helps. Most parts stores do this. Why buy one.
  • I have read the posts and appreciate the feedback. Unfortunately I am not sure what I would do with a scanner if I had it. If I bought one, used it according to the manual, then what? It gives me some codes, I read them, don't know what to do about any of it. Don't know what would happen if I re-set the codes. Does that make the check engine light go out? So it would pass smog?

    I don't have an O'Reilly in my part of California. Anyone else know of somewhere they do this. Like a Kragan or Pep Boys?

    Since this seems to be a common problem, what does Subaru say about this? :)
  • OK.... I bought a scanner. And.... I have just made the trip from high-altitude to low and from cold to hot. I haven't got a CEL.... yet... but I usually get one within 24-48 hours after I make the trip.

    Of course, now that I have the scanner.... the car might just fix itself to spite me. :mad:

    I found the OBD2, 16 pin connector. Subaru "hides" it in plain sight. I was looking for some kind of hatch-cover but it's just THERE, next to the hood latch. I read somewhere that there are connectors that must be connected to put the car into test-mode. The connectors are supposed to be around the glove-box.

    True? Where do I find those? :confuse:
  • ateixeiraateixeira Posts: 72,587
    Nah, just follow the instructions that came with the scanner.

    I didn't need to find any connectors for any of the cars I've scanned. You just plug-and-play. Read the instructions to find out where to put the ignition switch and when.
  • xwesxxwesx Fairbanks, AlaskaPosts: 11,158
    I cannot offer feedback on most of your questions here, but as for "don't know what to do about any of it," I recommend that you simply write down the codes. You can read them without clearing them, which then leaves the codes in there. Or, you can read and then clear, which does turn off the CEL. Assuming no other problems, it should pass inspection.

    If you keep a log of the codes and dates/circumstances that may be involved with the code, you might be able to help a mechanic diagnose the problem. The codes themselves are symptoms and do not always point directly to the problem. If the light is on and you take it to a shop, they may very likely be unable to correctly diagnose and repair the problem They will, however, be far more likely to recommend work and throw parts at the problem.

    The code reader is not a replacement for repair and maintenance - it is a tool to assist those efforts.
    2014 Audi Q7 TDI, 2008 and 2013 Subaru Forester(s), 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup
  • ateixeiraateixeira Posts: 72,587
    Indeed, get the code and Google them, or come here and ask if others have seen it.

    It helped me trouble-shoot a bad ignition coil once.
  • andydgandydg Posts: 2
    Followed the advice here and now own a memoscan U480, read the codes and erased them putting out the lights. VDC, CEL, flashing cruise light. Codes noted in case it repeats.

    Thanks guys some great advice here.

    Andy in the UK
  • i have a 1995 lagacy L station wagon, my check engine light stays on all the time. I had it scanned and was told it was the air flow senser which is connected to the air filter box. I replaced it and still have the same problem. Anyone got any suggestions??? I'm at a loss. Thanks.
  • 2009buyer2009buyer Posts: 15
    I got rid of my 1996 in January because of the same problem and the propensity of garages to charge for things cars don't need. The dealership looked at mine under warranty way back when and could never find anything wrong with it. Several people on this forum have advocated to buy a scanner and then just clear the codes and the light goes out. But mine went back on after about 100 miles. So unless you have to have it smogged and have the light out for that, just ignore it and go your merry way. I think it is a flaw in the car since mine had that problem from about 45, 000 miles to 188,000 miles. Great car anyway.
  • ateixeiraateixeira Posts: 72,587
    Do you recall the error code? P0400 something like that?

    These codes are merely reporting symptoms of a problem, not the actual problem itself.

    For instance, you may get a catalyst operating below an efficiency treshold error, but it could be a bad spark plug that doesn't burn all the fuel, so downstream the catalyst notes the presence of too much oxygen in the exhaust stream.

    The code does not mean the catalyst is bad, however.

    If we have a code it might help narrow it down at least.
  • gilson1gilson1 Posts: 4
    my 2002 Subaru Legacy Outback 149k has been giving me cel errors since 102k. Always passes emissions...have put in 3 cat converters...last one was "customized with a bigger biskit" Drove 149 miles turned it off for 5 days. started it up and light back on. car runs perfect and always passes emissions. Muffler shop is working with me but we can't tell what it is...last time it was suggested that it may be running rich causing the cat con to get too hot (some discoloration). this is a pain in the a$$ because I can't trade it in or sell it with that light on. looking for suggestions
  • ateixeiraateixeira Posts: 72,587
    First I'd try to reset just the light, see how long it stays off.

    If that fails I'd reset the ECU completely, see if that lasts longer.

    Then just trade it while the light is off. ;)
  • xwesxxwesx Fairbanks, AlaskaPosts: 11,158
    Have the oxygen sensors been replaced? If not, I suspect one or both may be giving a "false positive" on the catalytic converter. I assume you are getting the P0420 code, "cat below threshold." That code is generated when the oxygen differential between the fore and aft sensors is not great enough. As a result, the problem could be due to an inefficient cat, or it could be due to the sensors aging and lacking the sensitivity to provide accurate readings.

    I had that code for 50,000 miles on my Outback. Tailpipe emissions were within spec that whole time, so I fully suspect the sensors were the problem. I was going to replace them in the spring of 2007 but alas, fate had other plans. ;)
    2014 Audi Q7 TDI, 2008 and 2013 Subaru Forester(s), 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup
  • dswissdswiss Posts: 11
    As you probably know, it could be a whole lot of things (last but not least one of the many oxygen sensors). Here is a little tip of what you can do to sell or trade it in: Reset the CEL by disconnecting the positive cable from the battery and shorting it for a few seconds to the chassis ground. Then reconnect it. That way the computer is reset and the CEL will be out and it will likely stay out for a few days.
  • gilson1gilson1 Posts: 4
    right on dswiss
  • xwesxxwesx Fairbanks, AlaskaPosts: 11,158
    Brilliant - dupe the next owner. We certainly need more folks with your mindset in our communities. :lemon:
    2014 Audi Q7 TDI, 2008 and 2013 Subaru Forester(s), 1969 Chevrolet C20 Pickup, 1969 Ford Econoline 100, 1976 Ford F250 Pickup
  • bobny57bobny57 Posts: 30
    After almost five years of trouble free driving I had the CEL flash.

    The dealer scanned it and reported Codes P2016-2021 Tumble Position Sensor 1&2 which would cost $611 plus tax to fix.

    My local mechanic is going to do the repair for $450 plus tax.

    Question: What is a tumble position sensor.

    Thanks for all the good advice you've given us over the years.
  • bobny57bobny57 Posts: 30
    An additional question regarding the tumble sensor: Is there anything I can do to insure that after I replace these sensors they won't be damaged again. For instance, should I replace my air filter, spark plugs etc.?

    Thanks again,
    Bob Woods
  • tommy69tommy69 Posts: 2
    i get a code saying misfire cylinder 3. any suggestions?
  • I recently got the Check Engine light in my 2001 Subaru Outback. I read the code and got two of them:

    P0328 - Knock sensor circuit high input
    P0420 - Catalyst System Efficiency Below Threshold

    I'm not familiar with a Knock circuit but know it has something to do with ignition. I also know that the cat converter codes can go on an ignition problem. I'm weary to take this to a mechanic shop (since I haven't found a good one yet) and know they'll just try and get me to buy a whole new cat converter.

  • ragozcyragozcy Posts: 1
    Hey simonbones, a knock sensor is a piezioelectric sensor (when vibrated produces voltage). It's located directly on the engine block (usually right above cyl. 4) and senses misfires (engine knocking). It's odd you didn't get a misfire code, though, has it been running really rough in the past? Usually if it misfires badly enough, it'll knock out your knock sensor (P0328 almost always means the knock sensor is hooped, new one'll cost you anywhere from $180-$350) and consequently the extra fuel from cylinder that isn't firing will overheat and kill your cat (P0420). You could dish out the cash for the knock sensor, then ask around at exhaust shops for options on a new cat (or straight pipe with cheater chip)
  • golinegoline Posts: 9
    For almost 2 years my mechanic and I have been trying to fix this problem. We started with the gas cap. Then replaced the filler tube and valve and solenoid. The light stayed off for about 240 miles.

    After a smoke test (at another shop) we were told it was the fuel valve solenoid (again), that was replaced along with some canister that was attached to it and falling apart. The light stayed for a bit over 500 miles.

    After another smoke test last week (again, different mechanics shop...but same smoke test place), we're told it's the fuel filler tube and valve, again!

    I have started smelling gas over the past few months, did not smell it previously.

    As someone else mentioned, NYS has an annual safety/emissions test and my mechanic has had to work around my inspections to get the light off so I can drive a certain amount of miles and then hopefully pass the inspection before the light comes on again.

    I'd just keeping driving till next spring and inspection time, except for the gas odor which now has me scared.

    We also have a Forester and if and when I replace the OB, I will not buy another Subaru, even though we've love them up until this frustrating and expensive experience.

    BTW, my mechanic is well-known and respected in our area and I (kind of) have full confidence in him....I have another appt. with him on friday to bring the bugger in. ARGH!


  • golinegoline Posts: 9
    "it's what makes a Subaru, a Subaru." :cry:

    After my mechanics fourth attempt(in 2 years) to get the evap code off for good...after 82 miles it's back on again. I am not happy. :mad:
  • dswissdswiss Posts: 11
    here's a little tip:
    you can reset the check engine light by disconnecting the positive (red) wire from the battery and hold it to the ground for a second. Then reconnect. This will reset you computer. I did this just before inspection, and again before trade-in.
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