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Old 04-13-2004, 10:46 AM   #1
EZar
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Default P0171 and P0136 (too lean and rear o2 sensor) on stock 2.2L impreza - any ideas

I have (well, my girlfriend has) a 2001 Impreza L (2.2L) throwing P0136 and P0171 - rear O2 sensor malfunction and running too lean. This is completely stock with ~50k miles. Driveability is fine, but with reduced gas mileage.

The only culprits I can come up with is:
- MAF is dirty or dying
- Front O2 sensor is dying

Does anyone know of a way to diagnose this?

Thanks!
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Old 04-13-2004, 10:49 AM   #2
marcus12
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rear O2 sensor malfunction may require the replacement of that O2 sensor, only. That could also be causing you to run lean.

Try replacing the rear O2 and clearing the CEL - see if it comes back after that. If it does, I'd suggest replacing the front O2 sensor as well. They usually go bad at around 30K miles.

//marcus
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Old 04-13-2004, 12:56 PM   #3
EZar
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Default thanks!

Will try replacing the rear first.

Is there any better place to buy these than the subaru dealer? There doesn't seem to be a Bosch replacement for the 2.2L sensor, only the 2.5NA and the 2.0T.

Thanks.
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Old 04-13-2004, 12:56 PM   #4
1 Lucky Texan
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Probably get the dealer to fix it under emissions warranty.
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Old 04-13-2004, 01:05 PM   #5
EZar
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Unhappy warranty is up unfortunately

It has 51k miles, and Carter Subaru told me it's part of the bumper to bumper, not powertrain or emissions
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Old 05-13-2004, 12:17 PM   #6
Pocon
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I had the exact same codes on my RS-T...

P0171 was solved by getting bigger injectors. I'm running a STi fuel pump + ECU so the stock WRX injectors couldn't deliver. Maybe your g/f's car needs the injectors cleaned or something.

P0136 I bypassed the rear stock O2. Instead I'm using a AEM wide band gauge controller. I'm thinking my swappers didn't tap a signal to the ECU, thus, tricking the ECU into thinking the rear O2 is bad.

Good luck!
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Old 05-13-2004, 01:40 PM   #7
SjYankee006
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How long has the CEL been comming on for? Don't wait too long (over a month) before replacing the O2 or she might start having some more serious driveability issues... I had the same problem, with the same 2 codes and after about a month, the sensor must have finally died because I could barely drive my car. I managed to limp it into the dealership and ended up having to pay $200 for a new O2 ($100 plus $100 for install). It did clear up both codes though. (I have a CAI and cat-back)....
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Old 05-15-2004, 02:32 PM   #8
Charlie-III
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Hmmm....reread the manual under "emission warranties". Since the O2 sensor is emission related, it gets covered to a later date and higher mileage.

Do this ASAP.
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Old 05-15-2004, 10:53 PM   #9
Robin2
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For P0171, Vacuum leaks? Clogged fuel filter?

For the P0136, it's the rear O2 sensor... just changed mine about a month ago on my RS... It was an NGK direct replacement one...

Robin
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