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1999 Forester
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3 Posts
Discussion Starter #1
Hello All,
I noticed the CEL light after a trip from Boston, MA to south MS (the car with ~50,000 miles on it has been in Boston for the past 10 years). The gal at Autozone plugged in her device and read codes P0135 (Front O2 Sensor) and P0170 (Fuel Trim). Should I go with the exact fit sensor or it is worth the savings to try the universal? Also, could a bad sensor be adversely affecting my mpg? I also plan to go ahead and replace fuel and air filter as well as plugs and plugs wires while I am at it. Thanks in advance.

SB
 

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Registered
2005 Impreza RS Wagon Auto
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3,683 Posts
Hello All,
I noticed the CEL light after a trip from Boston, MA to south MS (the car with ~50,000 miles on it has been in Boston for the past 10 years). The gal at Autozone plugged in her device and read codes P0135 (Front O2 Sensor) and P0170 (Fuel Trim). Should I go with the exact fit sensor or it is worth the savings to try the universal? Also, could a bad sensor be adversely affecting my mpg? I also plan to go ahead and replace fuel and air filter as well as plugs and plugs wires while I am at it. Thanks in advance.

SB
The front sensor controls fuel ratios so yes it does affect mileage when it goes off the deep end. Sounds like a bad sensor by that code combo. Get the direct fit and save yourself a headache.

Replacing plugs/fuel filter never hurts and with that mileage could use a new set.
 

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Registered
1999 Forester
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3 Posts
Discussion Starter #3
Thanks for your response. The front O2 sensor is before the catalytic converter, and the rear O2 sensor (after cat. conv.) is not as important right? I will most likely borrow the tool from Autozone or O'Reillys, but I read somewhere here that the replacement can be done without it. Thanks again for the information.

SB
 

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Registered
2005 Impreza RS Wagon Auto
Joined
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3,683 Posts
Thanks for your response. The front O2 sensor is before the catalytic converter, and the rear O2 sensor (after cat. conv.) is not as important right? I will most likely borrow the tool from Autozone or O'Reillys, but I read somewhere here that the replacement can be done without it. Thanks again for the information.

SB
Correct, the front O2 sensor is Pre-both cats and that is the crucial one, the rear (post-cats) is just for emissions purposes (is the cat working/not). The tool u can borrow makes it easier but it can be done without. Get the set that comes with both the 1/2" and 3/8" socket because depending how you go at it you will need different sized wrench.
 

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1999 Forester
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3 Posts
Discussion Starter #5
Thanks again. Its awesome speaking with someone who knows what they are talking about .... not too many Subarus in South MS.

I went to Subaru Genuine parts dot com as it they are cheaper than the local Autozone or O'Reillys and found the front O2 sensor and it says:

Order By Description.
Electrical - Powertrain control - Automatic transmission - Oxygen sensor

My car is manual, but does that make any difference? Thanks again.
 
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