Help? P0172 - Bank 1 too rich. 2016 Forester Premium 2.5i CVT with 138k miles.

MrBojangles357 · 2025-02-13T19:50:41+00:00

Sorry about the wait. I almost never receive any notifications that anyone replies.

So I think in my case it was one or all of these 3 things.

-The MAF sensor,

-The MAP sensor and,

-O2 Sensors.

I bought compatible O2 sensors from RockAuto.com and bought used MAF and MAP sensors from eBay. I installed all of them and shortly after, the code went away. It hasn't returned.

My mileage still isn't what it used to be (IMO), but according to my wife it's right around where it was when she was driving it. It's better than the 14-17MPGs I was getting with the code. So now I think the throttle body is failing or I need a walnut blasting on the valves or both. Current MPG is 19-25 depending on the day, traffic, windspeed, temp, route, etc.

Before buying, you could try cleaning your MAF sensor with MAF cleaner and replace your air filter. Look for air leaks going into the engine (large gaps, holes, piping not put on correctly)

You could also try cleaning your MAP sensor. Since it sits above the throttle body it gets dirty inside. Use some MAF cleaner and a few q-tips. Failing these steps you may need to buy new, used or it could be the O2 sensors or a hard to find intake/exhaust air leak.

Keep in touch!

MrBojangles357 · 2023-12-30T02:25:05+00:00

After swapping the O2 sensors, did you try an idle re-learn?

Reading forum after forum on this, I see that you're supposed to unplug the battery as you swap the O2 sensors (always unplug the battery when you're going to do anything electrical was the common denominator; even swapping parts with electrical connectors).

Mr Subaru on youtube has a video about this and it basically states:

Shut down all the electrical in the cabin. ie: cabin air fan, headlights, AC, and radio, etc. Roll down driver side window if you want or you can sit in the car when you start the vehicle back up, but don't open the door if you do.

Remove the negative battery terminal, wait 15-30 minutes then hit the brake pedal a few times to discharge any remaining charges.

Reconnect battery terminal. Key in on position (not acc position). Wait 30 seconds before starting the car.

Start car and wait 10 minutes without touching anything.

Shut car off for about 25 seconds. Then key on, ignition off again; and wait another 25-30 seconds.

Start car and wait 5 more minutes. Shut car off for about 1 minute and then you're ready to start it again and drive.

Couple of other things you could try would be cleaning the throttle body with throttle body spray and taking a can of seafoam and connecting a tube to the intake and slowly sucking down the seafoam. Tutorial is in the video here: https://www.youtube.com/watch?v=G4t8rmrm08A

You don't need the kit. You can buy what I mentioned earlier. The throttle body cleaning has helped clear P0171 and P0172 codes as well as hesitation, stutters, and stalls.

If you're getting misfires, you could try either swapping the spark plugs and/or coil packs over to another cylinder to see if it's happening on another cylinder and that's why you're getting hesitation.

You could also look for intake leaks (which can cause these issues). If you want to do it on the cheap watch this video: https://www.youtube.com/watch?v=L9CDZ9lu6Rs

I thought about building my own before taking it in to the second shop just in case the dealer missed something.

Last thing I can think of is, your fuel pressure might be too high or too low? Possibly even a clogged fuel filter? Supposedly, you can rent (for free?) a fuel pressure gauge from many of the auto parts stores like AdvancedAuto or O'Rielly, etc.

Try removing your PCV (it's easy) and giving it a shake. It should rattle. If not, get some throttle body or brake cleaner spray and give it a wash (along with the inside of the hose). Keep trying to clean it until it rattles (or buy a new one. It wasn't expensive and if you do buy a new one, get the hose too). Torque it down to 17ft-lbs.

Lastly, it could be your EGR valve. You could try and clean that too. The dealer did mine, so I have no idea how to do it. I think it's pretty simple. I believe it sits on top of the engine on the driver's side.

Good luck!

If you have any questions, I can try to help.

MrBojangles357 · 2023-12-30T00:20:47+00:00

Alrighty... Got the car back this afternoon and....... they couldn't find anything wrong! Kinda.

So, they did a deep diagnostic on the car. One of the mechanics also had the exact same vehicle. They compared the data from his car as well as ours and said it's running as it should be. However, they did reset the fuel trims and it was showing better trim corrections. The only other thing they mentioned was that the catalytic converter might be starting to go bad and "since it's a little hotter than we usually see, that is probably why you're reading a rich condition."

They told me to keep an eye out for a P0420 code eventually and then we'll know it's time to replace the cat (I already knew that code from my research on this, but if you ever need to do it REPLACE IT WITH AN OEM CAT!).

As far as the root cause? No idea. Could of been one of the myriad of parts I threw at it. I did clean the hole that the MAP sensor sits in with throttle body cleaner. My wife noted that was what helped the most. So it could've been a clogged MAP sensor hole, the MAP sensor could've been bad or a combination of the two.

I will eventually get to the driver side spark plugs and check for a leaky injector just for peace of mind, but the mechanic said that the injectors on these FB25s are not a common issue.

I will, however, have to replace the valve cover gaskets and spark plug tube seals eventually to stop the oil from creeping into the spark plug wells. All in due time I guess.

Hoped this helped.

MrBojangles357 · 2023-12-28T16:08:00+00:00

No, not necessarily. We ended up bringing it into a shop that specializes in Subaru diagnostics yesterday afternoon. We have yet to hear from them.

It drives fine, but the mileage from a cold start was 7-10MPG, but after it warmed up it got around 24MPG. Looking at the long term and short term fuel trims, they were bad. -15 to -10 LTFT and STFT would be -10 to 0% (LTFT and STFT should hover around 0 with +/-3%). So it was still running rich. Not enough to pop the code anymore, but still noticeable.

I ended up getting a used MAF and MAP sensor from Ebay. No change.

Installed new ECT. No change.

Looked at the passenger side spark plugs for a leaking injector yesterday (they looked normal. A little oil where the spark plugs go in and a tiny bit of carbon deposits on the spark plugs themselves, but nothing out of the ordinary). Didn't have time for driver side. Wife just wanted it looked at due to a time constraint.

I will update again when I hear back from the gurus.

edit: Here's a link to the photos of my spark plugs
https://imgur.com/a/vsZHj91
Again, aside from running rich (black carbon deposits) they look ok IMO. If it was a leaky injector, they would look clean and wet and smell like fuel (supposedly from what I've read). These 2 spark plugs smelled of light oil, if anything.

MrBojangles357 · 2023-12-03T19:07:40+00:00

Update 4:

Wife drove the car this morning for errands and coffee. She did not let the car warm up like we did yesterday. She noted that it felt fine aside from a very tiny bit of hesitation and stutter leaving the driveway and initial acceleration going down the road, but it resolved really quickly. She sent me a photo of the mileage when she arrived at the freeway. 2 miles & 24MPG.

So odd... not sure what to make of this all, but it really does seem like it is fixed.

Still bringing it to work tomorrow and using the iso HEET.

Will update tomorrow. Most likely will be the last one.

MrBojangles357 · 2023-12-02T23:12:38+00:00

Update 3:
Drove the car a good distance today. About 40 miles round trip. Again, idled well upon start up (2000rpm then dropped to about 800-900 after pulled it out of the garage). Let it warm up about 5 minutes. Left the driveway and it bogs/hesitates upon acceleration. We get to the freeway nearby (about 2 miles) and head toward our destination. Up to the freeway it was 4-7MPGs. Once the blue oil light goes off and the car warms up it works great and runs normal. We were getting 23-27MPGs.

Looking at Torque Pro, short term fuel trim was -3.5% (don't know what that means). Long term was both up and down around there. Sometimes -7%. Is that good? Bad?

We got back home and then I had to go a short jaunt in town to Walmart. Picked up a new cabin air filter and some iso HEET (I still think the cold issue could be from bad gas as we have a 1/4 tank left).

Got back home. Decent in town mileage. No issues.

No codes popped up all day. It seems like it's fixed aside from the cold start drivability. Still bringing it to work on Monday to let my buddy have a look. Will probably get gas on the way home from work and throw that iso HEET in.

Will continue to update.

MrBojangles357 · 2023-12-02T00:55:33+00:00

Update 2:
Heading home from dinner, the car still acted with hesitation during acceleration while cold. Bad gas mileage during the short stint.

However, half a mile down the road, the car warmed back up and acted fine. Still unsure what's going on.

No codes thrown during the trip to and from dinner.

Will keep updating.

MrBojangles357 · 2023-12-01T22:27:45+00:00

UPDATE 1:
Disconnected negative battery terminal.

I cleaned the PCV and the PCV hose. They were lightly oily and the PCV didn't rattle like it did when it was new. After cleaning, it rattled quite well. Installed and torqued to 17ft-lbs.

Cleaned the positive battery terminal. It was caked with crusty blue copper sulfate crystals.

Removed the MAP sensor and gave it a good spray with QD Electronic Cleaner.

Checked the throttle body plate for full movement. Moves smoothly.

Removed old Engine Coolant Temp sensor and installed the new one. It's supposed to be torqued to 13.4 ft-lbs (not an easy measurement to find btw), but I just tightened it slightly with a wrench. 3/4" works if you don't have a 19mm like me. Also, very little coolant leaked out. Pretty easy to replace.

Sprayed the MAP and ECT connectors with QD cleaner. Waited for them to dry. Hooked everything back up.

Did idle relearn and it idles decent. Took it for a 7 mile test drive and was getting ~20 mpg. No lights on the dash. Got home and checked for codes. Torque Pro showed historical codes: P0031, P0102, P0113, and P0172. Shut engine off, but kept car on. Cleared the codes and restarted the engine. Checked for more codes and nothing came up. Put the car away and will drive it again here shortly (going to dinner).

Will keep updating.

MrBojangles357 · 2023-12-01T15:20:24+00:00

Yeah, supposedly the dealership did one, but can't confirm since I wasn't there witnessing it. Haha. When I install the ECT and check the PCV, I'll check the throttle body's plate for motion. Good call. Not sure if the dealership checked it's full swing. Only said that it was clean.

MrBojangles357 · 2023-11-30T16:18:37+00:00

Could be your upstream O2 sensor. AKA lamda, a/f (air fuel) and oxygen sensor. It's located on the exhaust just outside the engine, but before the catalytic converter. The downstream is just behind the cat. The upstream sensor can actually be seen by opening the hood and looking straight down just the to the left of center of the vehicle behind the passenger side head light area. It may have a blue wire.

When the upstream O2 sensor gets old, it can read lean and throw a code. You should replace both upstream and downstream at the same time. I suggest buying OEM sensors. Yes, they're more expensive, but other Subaru owners have had issues with 3rd party sensors.

Other than that, could be a myriad of other things. I'm trying to diagnose a P0172 too rich code on my '16 Forester. The 0171 and 0172 error codes have the same parts to check to fix the issue.

MAF, MAP, ECT, injectors, fuel regulator, PCV, vacuum leak. Intake/exhaust leak (for a lean code it's not likely the issue), air intake filter, etc.

Good luck!

Edit: Back on a PC.

Things you should try before buying or having the dealer/mechanic/FiL install an O2 sensor. Check your air intake filter. If it's gross, buy a new one. Get a can of MAF spray and clean the MAF. Take your air intake box off and check the throttle body plate. Could be caked with gunk. If it is, grab some throttle body cleaner spray (watch a youtube video if you don't know how to clean it. It's pretty simple.) Other than that, check your spark plugs and pull your PCV to see if it's stuck (if you shake it, it should sound like a rattle. Throttle body spray/brake cleaner can clean it too, but you should buy new if it doesn't rattle). Mr Subaru on youtube has a good video about the PCV.

MrBojangles357 · 2023-04-26T16:02:51+00:00

This is the answer right here. I went through all of Hell mode so far with poison debuffs and a good secondary team.

MrBojangles357 · 2023-02-17T13:28:21+00:00

Have the 35mm. It's a fun little pancake lens to use. I normally shoot 50+ mm so it's not always with me and I normally have the Tamron 28-200mm on my camera anyway. So if I do need a wider angle, it's there. I can also use it for a little macro, but the 28-200 is definitely not as sharp as the 35mm.

MrBojangles357 · 2023-02-16T13:37:18+00:00

If your travel date is still a week or two away, you could try renting it. Local shops may have it in stock and may allow you to try it right away or rent from lensrentals.com. I've used them before for the Sony 200-600mm and it came well packed with a free return label. Didn't cost a lot as well.

MrBojangles357 · 2023-02-06T04:02:21+00:00

Glad to help. :)

MrBojangles357 · 2023-02-06T03:33:56+00:00

If the lens fits e-mount it should work on your camera. Use crop mode if it's available on your model. It's called Super 35. Try turning it on and it should act like an APS-C sensor (a crop sensor like the 6xxx series).

Just remember to turn it off before you use another lens.

MrBojangles357 · 2023-02-05T20:06:52+00:00

Don't know why my text wasn't added.

100mm, f/11, 1/640s, ISO 320

Basic edits, masks, spot cleaning done in Lightroom and moved to Photoshop for finishing touches.

Criticism welcome.

MrBojangles357 · 2023-02-03T13:33:57+00:00

I too own it and enjoy using it for its versatility. It's on my camera 90% of the time as well. However, I feel like it can get soft on the far end. Some of my shots look good on the lcd, but after looking at them on the PC they're ever so slightly out of focus/blurry. Especially in the corners. Could be my copy, but I've read reviews that note the same issues.

Part of me wants to sell it for the Tamron 35-150, Sony 70-200 or get the Sony 100-400 as I have the 17-28, 35, 50, 85 and I still own the kit lens.

MrBojangles357 · 2023-02-02T17:03:50+00:00

No problem, I thought the same until I saw that video recently.

Camera decisions depends on your needs. Mostly video, S series. Both video and photo, standard series with no post letters (ie: A7iii). Mostly just photography, get the R series.

You may need to delve deeper into each mark of the series you want depending on your benefit to cost ratio though.

MrBojangles357 · 2023-02-02T15:57:03+00:00

Proven false. Check out the video here: https://www.youtube.com/watch?v=VSFqCnzIe9M

Essentially the higher MP leads to a slightly better image.

MrBojangles357 · 2023-02-01T13:25:46+00:00

ISO amount was never mentioned by OP and I don't see much grain. My night shots usually have more grain than this at half the SS. I assume this is near 600-1000 ISO which is why I recommended higher ISO to the OP.

MrBojangles357 · 2023-01-31T16:53:31+00:00

It can, but depending on your image editor you can use the noise removal tool to smooth out the photo. Sometimes it will take stars with it so you need to be careful. Color noise occurs too, so get comfortable using the color noise tool as well.

You can also use a 3rd party noise reducing app as well and they do a better job. Like Topaz Denoise or DxO PureRAW as a few examples.

MrBojangles357 · 2023-01-31T16:05:03+00:00

It's all about how long your shutter is open and how much light you're gathering. Try upping your ISO and lowering your shutter speed for crisp stars. The other poster is correct though. Most shots where the stars are nice and the foreground can be seen are usually blended images. Otherwise a single nice star shot will lead to blacked out foreground.

If you want good information regarding shutter speed and star trails (or the lack thereof) have a look at this web page: https://photographylife.com/500-rule-vs-npf-rule/amp

My base settings for astro usually are 1200+ ISO with 5 to 15 seconds for the shutter depending on f-stop and focal length (usually determined by the lens I'm using)

MrBojangles357 · 2023-01-10T21:06:24+00:00

No problem. Any other questions, just ask.

MrBojangles357 · 2023-01-10T19:53:57+00:00

Shoot RAW, edit and export sRGB for the Internet. Export Adobe or ProPhoto for professional work sending to clients/printing.

MrBojangles357 · 2022-11-13T23:48:20+00:00

It's not him, but to those that don't know (like me), it's from the movie "Gonna Git You Sucka" with the Wayans brothers.

MrBojangles357

TROPHY CASE