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Old 02-27-2011, 01:13 PM   #1
azguard4
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Member#: 209934
Join Date: Apr 2009
Location: Phoenix, AZ
Vehicle:
1993 Subaru
Maroon

Default 1993 Legacy - Need Help With Emissions

I have a 93 Legacy with a CEL on. I checked the flashing codes myself and came back with an O2 sensor and knock sensor. When I took the car to the subaru dealership they said their data did not go back far enough to properly diagnose the car but they say they got codes for an O2 sensor, knock sensor and 2 Transmission speed sensors.

I can't find anything online about the 93 legacy having transmission speed sensors? Unless they were talking about VSS? Also they said fixing the knock sensor and O2 sensor would NOT cause the light to go out, is this true?

Any help is greatly appreciated.
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Old 02-27-2011, 01:40 PM   #2
Jessekrs123
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Join Date: Jan 2010
Chapter/Region: NESIC
Location: Oakville CT
Vehicle:
1993 Legacy Sedan
1984 BRAT

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Fixing the o2 sensor and knock sensor will make the CEL go away as long as there isn't a short within the harness. The nice part about OBDI is that the CEL is only tripped when the problem occurs, unlike OBDII where the CEL will stick around for a while even after it has been fixed.

The o2 sensor and knock sensor are common sensors that go bad on these old Subarus. You can definitely replace these sensors yourself, it is really easy.

Get a 7/8 o2 sensor socket, remove old one, put in a new one. o2s run like $20.

IIRC, the knock sensor is a 12mm and it is located under the intake manifold on the driver's side, way way down there. Simply remove the old one, and SNUGGLY tighten in the new one. Most common problem of this sensor failing is cracks, so don't tighten the crap out of it.

As far as your transmission goes, I'm assuming that it is an automatic transmission? If so is your power light constantly on? There is a way to diagnose transmission codes just like you would diagnosing CELs.

If you have any questions or need help reply back. I know these Legacys like the back of my hand.
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Old 02-27-2011, 01:47 PM   #3
azguard4
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Location: Phoenix, AZ
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Maroon

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THe transmission is auto and the power light is never on? Should it be? I'm stuck in a hard spot, the dealer says the "transmission speed sensors" will cause the light to be on. But I'm having a hard time believing it. I also can only find information about VSS on google, and everyone who says their VSS have gone bad have speedodometer and odometer problems, I have neither?

Thanks for your post and future help.
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Old 02-27-2011, 01:56 PM   #4
Jessekrs123
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1984 BRAT

Default

Speedo/Odo is ran by a mechanical wire on the older models, it is not electrical.

How does the car drive? I wouldn't believe your stealership, usually if there is a problem with the older auto trannies, your power light will stay on and then it can be diagnosed from there.

When you pulled the codes yourself you only got codes for the o2 sensor and knock sensor? The CEL also flashes codes for the transmission for example:
Code 33 - VSS
Code 51 - Neutral/inhibitor switch

If there was something going wrong with your transmission or your VSS, it would show up in your CEL codes.

Sounds to me like your stealership wants to suck you into fixing your transmission that has nothing wrong with it for some big $$$.
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Old 02-27-2011, 02:02 PM   #5
azguard4
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The car drives pretty good IMO. It's a little sluggish sometimes at a light, RPM's rev up when shifting into, 3rd, I think...But that could just be fluid, filter changed needed, maybe...I think the injectors need a good cleaning, spark plugs haven't been replaced since I bought the car in '09, so all those could be problems for the slight sluggish it has.

I pulled the codes by putting the key in and turning it to ON, I think that's the position and the light flashes, but it only has 2 sets of flashes...The was obvious, Knock Sensor 22 and the other 32 for O2 sensor. I will double check tonight when I get the car back from my ex. But like I said, there is only 2 sets of codes and I'm positive it does not flash a 33 for VSS.

So that being said, I should be able to replace the O2 and Knock tomorrow and the light will just go out?

My problem is if I put any money it the car I lose any money I would have to buy another 1K car lol...
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Old 02-27-2011, 02:07 PM   #6
Jessekrs123
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Join Date: Jan 2010
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Location: Oakville CT
Vehicle:
1993 Legacy Sedan
1984 BRAT

Default

Assuming that your wiring harness involved with the 2 sensors is not shorting out then yes, replacing the sensors should make the CEL go away.

The only reasons why a CEL is tripped in an OBDI Subaru would be the following:
- Sensor itself is shot to the point it cannot communicate with the ECU.
- The plug is disconnected from the sensor.
- The sensor is not properly grounded through the harness.
- The sensor is not receiving power voltage through the harness.

I would first test your harness to be sure that everything is being grounded. Do you have a multimeter, and if you do, do you know how to use it? I'm sure that everything is fine, but it's good to double check before spending money if you're strapped for cash.

You should definitely tune it up soon as well.
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Old 02-27-2011, 02:22 PM   #7
azguard4
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1993 Subaru
Maroon

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Yes my dad has a multi meter, he can figure out how to test the harness. I guess I'll have to soak on whether or not to put money into the sensors...thanks for the info, gives me another angle to look at this.
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Old 02-27-2011, 02:43 PM   #8
Jessekrs123
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Member#: 236927
Join Date: Jan 2010
Chapter/Region: NESIC
Location: Oakville CT
Vehicle:
1993 Legacy Sedan
1984 BRAT

Default

Yes, learn how to use the multimeter, it will be your best friend in any electrical application.

Also learn how to use a test light to test for voltage.

The sensors aren't too bad.

$20 for an o2 sensor (parts store)
$60 for a knock sensor (dealer)

Best of luck to you.
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Old 02-27-2011, 03:22 PM   #9
elkaboom
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Location: Akron, OH.
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90 Legacy
Misty Dawn

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I have a 90 Legacy, and some time ago, I was throwing a code for the O2 sensor. I kept on putting it off, but finally I went out and got a 3 wire replacement from NAPA. It's painfully easy to replace. Unless you've modded your exhaust, it's a very straightforward repair. In my case, I was having a few other issues, so it took awhile to track it down to the O2 sensor directly, but ultimately, that was the cause.
Regardless, the O2 sensor itself shouldn't take you more than 10-15 minutes of fiddling around. It's very accessible.
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