P0171 code (system too lean bank 1)

Hi everyone. I have a 2014 Legacy 2.5 premium with about 60,000 miles and I got a check engine light the other day and it came out to be a P0171 code. I was having some drivability issues for a while where the car would run very rough whenever it would come to a stop. Just wondering if anyone knows what could be wrong, I replaced the air filter (with an aftermarket performance filter, not sure if thats a good idea?) after the light came on, the filter was dirty but it wasn't THAT dirty... I also cleaned the MAF sensor with some MAF sensor cleaner. I haven't yet erased the code but I'm wondering if it comes back on any ideas on how I should proceed?

misfire on any cylinder?

misfire on any cylinder?

 

No no misfire on a particular cylinder but the engine felt like it wanted to stall and vibrate a lot when I would come to a stop. I’d even loose brake pressure sometimes.

Do a smoke test for air leaks?

 

!

 

 

Update:

 

After changing the air filter and cleaning the MAF sensor it seems to be running better. The car doesn't seem to want to stall anymore when stopping so I guess the issue was a dirty MAF, I'll be keeping an eye on how the car behaves for a while.

Update post update: Check engine light is back on

 

Any ideas on how to proceed? Maybe the aftermarket air filter is the issue, maybe a vacuum leak somewhere?

Edited January 22, 2021 by 5thGenCVT

Do a smoke test for air leaks?

 

 

 

 

 

Is that expensive?

Is that expensive?

 

It would be best to have someone else do it (a shop who paid for the equipment to test). You're testing to see if you have vacuum everywhere. You might have a hose that let go/disconnected, you might have a pinhole air leak in a hose, you might have an o-ring on a sensor that let go... it goes on.

It would be best to have someone else do it (a shop who paid for the equipment to test). You're testing to see if you have vacuum everywhere. You might have a hose that let go/disconnected, you might have a pinhole air leak in a hose, you might have an o-ring on a sensor that let go... it goes on.

 

Thanks! I’ll inspect all the hoses and get that smoke test done. Just have to find who does those in my area

Is that expensive?

 

Sorry, that was about the other guy's user name lol.

 

Smoke test shouldnt be too much. There's a diy around here, search boost leak test here or online.

 

You can do it with an air compressor too.

Sorry, that was about the other guy's user name lol.

 

Smoke test shouldnt be too much. There's a diy around here, search boost leak test here or online.

 

You can do it with an air compressor too.

 

Thanks I'll check it out

Here ya go:

https://legacygt.com/forums/showthread.php/easy-5th-gen-gt-boost-leak-test-255163.html

Update: So I took the car to my local Subaru dealer to get the check engine light checked out and got it fixed. Apparently there is an ECU update for the 5th gen Legacy that they installed and it took care of the check engine light code and stalling issues. It's only been a few days but the car doesn't seem to be stalling anymore, I'll continue to monitor it and post more updates as time goes on.

Update: So I took the car to my local Subaru dealer to get the check engine light checked out and got it fixed. Apparently there is an ECU update for the 5th gen Legacy that they installed and it took care of the check engine light code and stalling issues. It's only been a few days but the car doesn't seem to be stalling anymore, I'll continue to monitor it and post more updates as time goes on.

 

What is an ecu update and what did that cost?

When the engine management computer gets a system update, similar to your home PC getting an update.

 

I semi doubt that it would solve your issue any more than unhooking the battery for a couple minutes would, but if it solved your issue, then sweet!

What is an ecu update and what did that cost?

 

Basically what Pleides said, it's a software update that they apply to your engine control module. And they only charged me for the visit, so it was $140 for me. Just curious, what year is your car?

Edited February 6, 2021 by 5thGenCVT

When the engine management computer gets a system update, similar to your home PC getting an update.

 

I semi doubt that it would solve your issue any more than unhooking the battery for a couple minutes would, but if it solved your issue, then sweet!

 

Here's hoping! I do wonder what was in that update though...

Does it provide any information on your receipt on what they installed/updated, such as a software version or a TSB number or anything like that? Did they mention finding anything loose, disconnected, or plugged?

Does it provide any information on your receipt on what they installed/updated, such as a software version or a TSB number or anything like that? Did they mention finding anything loose, disconnected, or plugged?

 

No it doesn't go into detail on the software update. All that it says on the description is that the CEL was inspected and gave the P0171 code and they performed an ECM update. They didn't mention anything about loose hoses or anything either.

I just purchased a 05 Legacy GT. And while driving it hope this P0171 light came on. After my mechanic chased this problem for quite a while. He finally discovered there was a leak on the underside of the top mount intercooler. Found 1 at junk yard for $75, got it put on the car and the SES light has went out. Hope this helps.

 

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I just purchased a 05 Legacy GT. And while driving it hope this P0171 light came on. After my mechanic chased this problem for quite a while. He finally discovered there was a leak on the underside of the top mount intercooler. Found 1 at junk yard for $75, got it put on the car and the SES light has went out. Hope this helps.

 

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Not me because my car is a non turbo lol, but hopefully someone can find it helpful

Okay Legacy guys and gals. Update on my P0171 problem. After changing the top mount intercooler, I drove the car for a bit and the code came back on. I then replaced the intake gaskets, and ordered and replaced the exhaust gaskets at the headers with a set of grimmspeed gaskets because they were a bit thicker. You could clearly see the blow by on the older gaskets. I also replaced the oxygen sensor as it wasn't reading right. After pulling the the oxygen sensor there're were was appears to be grinding marks on the the sensor. Well I'm happy to report that I've driven the car for about 160 miles and the light hasn't come back on.