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Old 12-18-2015, 02:42 PM   #1
Konfusi0n
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Exclamation CEL P0171 - Exhaust leak near O2 sensor?

CEL: P0171 - System Too Lean (Bank 1)

Car has a high idle RPM (around 2k) when turning on and a rough idle after warming up, fluctuating around 500rpm causing it to almost die.

I have an exhaust leak at the gasket near my front O2 sensor. I suspect that this is causing the CEL. I'm away from home at the moment and the muffler shops near me don't carry the gaskets and neither do the auto parts stores. There are no Subaru dealerships within ~50 miles of me. How far might I be able to drive my car safely and will excess air leaking into the exhaust cause any damage to the engine?
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Last edited by Konfusi0n; 12-18-2015 at 02:48 PM.
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Old 12-18-2015, 05:00 PM   #2
yarrgh
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Is the leak before the sensor? Then yes, it's causing the CEL. I find it hard to believe that parts stores don't have a similar gasket. You don't need an exact match. If you can't find anything close, there is a product that helps with exhaust gaskets, it's sort of a coppery, puffy-type product. The name escapes me at the moment. It'll get you a temporary fix.

Worst case, you can unplug the sensor and the car will run rich for safety. It's not efficient, but it'll do.
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Old 12-18-2015, 06:29 PM   #3
Konfusi0n
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Could I unplug the MAF and get the same result?

The exhausts shops that I went to turned me down for some reason and told me they don't carry gaskets for these cars. Not sure why but apparently one contacted some auto parts stores and they didn't have any in stock. Unfortunately I need to head home within the next two days so I can't just get them ordered unless I wait around a bit.

EDIT: Unplugged MAF and car ran awesome except for a good bit of turbo lag. No rough idle or anything. I'll just drive home running rich and I'll be fine.

Last edited by Konfusi0n; 12-19-2015 at 11:14 AM.
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Old 06-03-2021, 09:45 PM   #4
sebastian323
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Quote:
Originally Posted by Konfusi0n View Post
Could I unplug the MAF and get the same result?

The exhausts shops that I went to turned me down for some reason and told me they don't carry gaskets for these cars. Not sure why but apparently one contacted some auto parts stores and they didn't have any in stock. Unfortunately I need to head home within the next two days so I can't just get them ordered unless I wait around a bit.

EDIT: Unplugged MAF and car ran awesome except for a good bit of turbo lag. No rough idle or anything. I'll just drive home running rich and I'll be fine.

Does unplugging the MAF force the car into open loop ?
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Old 06-04-2021, 08:25 AM   #5
Elbert Bass
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Quote:
Originally Posted by sebastian323 View Post
Does unplugging the MAF force the car into open loop ?
Yes, any time the check engine light is on the ECM is in open loop. You are also in open loop during initial cold start and at WOT.
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Old 06-20-2021, 08:34 PM   #6
sebastian323
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Originally Posted by Elbert Bass View Post
Yes, any time the check engine light is on the ECM is in open loop. You are also in open loop during initial cold start and at WOT.

im quite sure you can have some CELs for things like the TGVs and still get closed loop operation. it also seems like you still get closed loop with the MAF disconected. this can be verified by monitoring CL/OL status in romraider
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Old 06-22-2021, 08:50 AM   #7
Elbert Bass
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Originally Posted by sebastian323 View Post
im quite sure you can have some CELs for things like the TGVs and still get closed loop operation. it also seems like you still get closed loop with the MAF disconected. this can be verified by monitoring CL/OL status in romraider
The whole purpose of disconnecting the MAF is to put the ECM in open loop as an initial diag indication. That's one of the first things Subaru teaches in diagnostics. Like you say - monitor open/closed loop PID. I would urge you to do and get back to us on that.
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