The check engine light on my recently acquired 90 Legacy lights up about 10 minutes after starting the vehicle. Sometimes it stays on, while at other times it goes out again. The car runs fine and everything seems normal. How can I troubleshoot this? Do I need a special tool to read diagnostic codes? Thanks for any suggestions.

There Was A post out there about this... But i cant find it... So heres the link on what to do!! Very Good Site.. http://www.surrealmirage.com/subaru/subaru.html

Hes in here all the time.. I just did this tonight after i read The post!! Very cool.. I have a 12 code.. starter issue.. BUt ya read that, it you should find out what is wrong!

yup....check the codes and see what you find.

Turn car off

 

Plug the 2 black harness' togheter under the dash (between TCU and ECU)

 

Turn car to ACC position (do not start)

 

CEL will blink the codes.

 

Unplug harness

 

Fix the problem

 

Put many more miles on your car.

Thanks for the replies. I'll try reading the codes in the next few days and post my findings.

OK - I finally got the car from my 16 year old son and a day off to read the codes. I had to let him drive my 2002 Tundra to school today though!

 

Anyway, I connected the 2 ends of the black connectors using the chart and instructions from http://www.surrealmirage.com/subaru/subaru.html

I have 6 codes cycling in this order:

33 - Abnormal reading from vehicle speed sensor

35 - Canister purge solenoid valve inoperative

12 - Abnormal reading from starter switch

21 - Abnormal reading from water temperature sensor

23 - Abnormal reading from air flow sensor

24 - Air control valve inoperative

 

I believe these are historical problems that have occurred and been stored in the diagnostics system. My son had an overheat problem due to the radiator cap not being screwed on properly. And we found a connector on top of the engine, directly behind the air conditioner compressor disconnected.

 

My question now is should I erase these codes and check them again? I believe I may have a truly faulty solenoid valve and/or air control valve, but that the other abnormal readings are just historically stored fault codes.

 

Thanks for the help!

here was that post you were talking about:

http://www.ultimatesubaru.org/forum/showthread.php?p=158817#post158817

yeah,

 

clear the codes, and see what comes back.

Thanks for the replies Legacy777.

 

I erased the codes... twice. The first time I initially got the all clear signal (steady flash at 1/2 second intervals), then started getting something else after about 3 or 4 minutes of driving.

 

The second time I only drove for about 2 minutes and I got the all clear signal only. Then parked the car, turned it off and disconnected the green and black connectors.

 

However, I am still getting all 6 trouble codes mentioned earlier when I connect the black connectors back up.

 

What do you think?

Are the codes active codes? Like is the CEL blinking while you drive? Or do they just show up again when you check the black connectors?

 

if the CEL isn't on, or blinking while driving, then these codes are probably stored codes, and not active.

 

Try disconnecting the EGI/TCU fuse (which I think is fuse # 14 at the driver's kick panel) for 30 minutes. Drive the car around, and then check codes again.

Your procedure for clearing the alarms from memory call for driving the car over 10 mph for one minute while the black and green connectors are connected. My trip around the block takes a bit longer than one minute.

 

I get the "all clear" if I drive for just 2 minutes. If I continue driving for a couple minutes longer, the "all clear" 1/2 second flash changes to the alarm codes. So, I assume they are active alarms.

 

With the connectors disconnected I get the intermittent CEL like I described in my first post.

 

I also tried resetting the modules using your procedure that calls for disconnecting the negative terminal as well as removing fuse 14 for an hour or so.

 

Thanks again!

I also tried resetting the modules using your procedure that calls for disconnecting the negative terminal as well as removing fuse 14 for an hour or so.

 

Thanks again!

So with the fuse and battery method the codes came back right away?

Yes - That is correct.

 

It seems like they must all be real faullts, but I don't think so. I had thought that some of the abnormal sensor readings would have cleared. Especially the abnormal water temperature. The water temp is okay.

 

I'm pretty certain all those sensors aren't bad either. We have had the car for 2 months and just recently started getting the intermittent CEL indications.

how does it run? Is there anything out of the ordinary?

The car runs great. Nothing out of the ordinary, other than the CEL coming on.

 

Oh, there is one thing that I have failed to mention: When I had the black and green connectors connected, the engine cooling fans came on when I turned the key to the accessory position.

Yeah, that's normal for the fans to be on.

Hi,

I would check that the plugs are right in at the computer and that they havent got wet and corroded. It's just a guess but the problems indicated are not really related except that they all come together at the computer.

I have the same problem with my legacy. Haven't had a chance to check the trouble codes yet. The car runs great, no problems what so ever except for the CEL that lights up sometimes when I start the car. It lights up and stays on. If I shut the car down and turn in back on it sometimes dissapears and sometimes stays. A bit annoying, indeed.

I have the same problem with my legacy. Haven't had a chance to check the trouble codes yet. The car runs great, no problems what so ever except for the CEL that lights up sometimes when I start the car. It lights up and stays on. If I shut the car down and turn in back on it sometimes dissapears and sometimes stays. A bit annoying, indeed.

check the codes and let us know what you find.

I am guessing noc sensor or injector

Sorry I took so long to post back, but the problem is fixed! The computer was faulty. I replaced it and all codes are gone! Thanks for the replies.

Thanks for posting back!

I still haven't been able to figure out the problem so maybe it's that.