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Old 12-31-2013, 09:19 PM   #1
Scoobisaurus WReX
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Default Help diagnosing CEL and wiring issue

2005 WRX Wagon, Cobb TBE, Invidia DP, AP Stage 2 93 off-the-shelf tune, Cobb sways and adjustable perches. 88k miles. Have owned it for over a year and since and 71k miles.

So the problem started by throwing P1400 and P1420 (fuel tank pressure control valve solenoid circuit high and low, respectively). Every time i would reset the ECU the light came back on immediately... so I found this thread... http://forums.nasioc.com/forums/show....php?t=2310341

Sure enough I dug in to the wiring loom and found a broken wire. It had been repaired previously similar to this thread, but the joint was broken (or just not soldered in the first place). It looks like the harness was rubbing on my sway perches and wore through. Soldered it, heat shrunk, taped, reinstalled, and reset ECU. Light stayed off for a few days, about 100 miles, and came back on. Convinced my solder job was crap (did it at night) i tore it apart again, did a solid solder job, tested all connections, and reset again. Same story. Next step was replacing the solenoid itself. I thought maybe if it had been constantly shorting it may have siezed. No such luck. The old solenoid tested at 25 ohms (FSM says 10-100), seems to operate normally when blowing/suck on each port. Confirmed by comparison to the new dealer part.

Then i remembered i had seen something odd in one of the wiring harnesses under the rear seat when i thought i had a fuel pump issue (turn out to be just a fuse). Anyway i tore out the rear seat to expose the harness, and sure enough there was tape wrapped around a yellow wire with green stripe (same as one of the wires to the solenoid) where someone had made a previous repair. Taking off the tape i saw this (see pics)


http://postimg.org/image/r8r5ql1vf/

http://postimg.org/image/84xua8p17/

This is the harness under the passenger side. Coming from the ECU is one wire, yellow with green stripe. The crimp connector goes to three more yellow/green wires in the loom that goes down through the floor and toward the solenoid. I suspect making a hard solder connection here will solve my now intermittent CEL. Anyway, I am terrible at reading wiring diagrams and am trying to figure out how these wires were connected originally.

Can anyone help me out, or post a pic of the same harness unmodified in your own car? Its as simple as popping off the two little plastic button caps down in front of the rear seat and undoing to 12mm bolts beneath them. The seat pan slides right out and the seatbelts thread through the holes.
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Last edited by Scoobisaurus WReX; 12-31-2013 at 09:26 PM.
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Old 01-03-2014, 01:26 PM   #2
Cougar4
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I suggest you solder that splice connection and then tape it carefully to keep any moisture out of the connection.
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Old 01-03-2014, 02:04 PM   #3
Scoobisaurus WReX
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Agreed, and I was planning on doing so, I am just really curious what that connection is supposed to look like from the factory. I am really not sure why the original owner would have messed with it, and want to make sure its actually wired correctly. I am not sure where the other two similar wires go either.

Interestingly this particular solenoid is not on 02-04 wrx's. Not sure about 06-07 or STi's. There is a similar (much cheaper) part in its place.

The connection had some blue tape over it (didnt really seem like proper electrical tape). The crimp is really well done though FWIW. I tested resistance between the one wire from the ECM and each of the 3 wires that run under the car and all test the same (cant remember the value but some small amount of resistance). Given its an intermittent issue though i guess that doesn't mean much.
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Old 01-03-2014, 02:56 PM   #4
Cougar4
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There are splices made in the factory wire that look basically just like that.
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Old 01-03-2014, 03:48 PM   #5
Scoobisaurus WReX
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10-4 i'm betting its factory then, thanks. Cant hurt to replace it and see what happens anyway!
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Old 03-05-2019, 06:16 PM   #6
jgal
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Default any resolution?

I know its an old thread, but I'm going through a similar problem with my 06 forester x.

what was the fix?
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Old 03-05-2019, 07:29 PM   #7
Mulder
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Last post was in 2014, last login 2017. Don't expect an answer.
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Old 03-06-2019, 11:36 AM   #8
Scoobisaurus WReX
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So I did eventually figure out the issue, or rather Turbo Time did after I gave up. There was a wire on top of the gas tank that had broken. Dropped the tank and fixed that, but it continued and he was able to diagnose one of the boards in the ECU had fried likely as a result of the broken wire. Luckily he had a known good used ECU on hand which he sold to me and installed. Never had it come back up again. He was of the opinion that someone had been into the harness prior to my ownership, but I have no idea why they would have. Sold the car this past summer to get something bigger for the family.

I wish I could tell you the fix was easier, good luck.
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Old 03-06-2019, 12:11 PM   #9
Mulder
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Thanks for coming back and posting the resolution. Guess you got a notification for the thread? People usually don't return after that long.
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Old 03-06-2019, 12:47 PM   #10
Scoobisaurus WReX
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Yea got an email. As a frequent lurker who runs into dead end threads a lot I hope that by resolving this one I will earn some Internet karma
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Old 03-06-2019, 01:41 PM   #11
Charlie-III
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Quote:
Originally Posted by Mulder View Post
Thanks for coming back and posting the resolution. Guess you got a notification for the thread? People usually don't return after that long.
Totally agree!

Quote:
Originally Posted by Scoobisaurus WReX View Post
Yea got an email. As a frequent lurker who runs into dead end threads a lot I hope that by resolving this one I will earn some Internet karma
Yes, thanks, as you mentioned there are waaayyyy too many dead end threads.
Many of us appreciate you closing this out.
Yes, you get Internet Karma points......use them well.....


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