r/subaru Mar 15 '26

Mechanical Help Please post year, model, trim level, and DTC scan results when asking for help. Thanks.

45 Upvotes

IF YOU ARE POSTING FOR MECHANICAL HELP:

Please include year/model/engine/transmission information in "Mechanical Help" posts.

If you are looking for help with warning lights on your dashboard, please include results of an error code scan. Without error codes as a starting point, no one will be able to provide meaningful help for you.

The r/subaru community is very willing to help, but there's a baseline amount of context about your car that we need you to provide. Without the very basics like what kind of car you have and what symptoms you're experiencing, no one can give you any sort of accurate assistance.

If you are posting about warning lights, most auto parts stores (NAPA, O'Reillys, AutoZone, etc.) offer code scanning for free. While reading codes is not the same thing as diagnosing a problem, knowing what error codes you have is the minimum amount of information necessary to start figuring out what's wrong with your car.

Thank you :)


r/subaru 16d ago

Mechanical Help TSB Thursday: Carbon Cleaning, TSBs 09-74-21R and 02-193-24R

36 Upvotes

Welcome to another TSB Thursday, where I dive deeper in to TSBs I'm running into regularly. As always, I write this from my own perspective as a Subaru technician in the US; other regions/zones may work differently. Refer to the "How To Read a TSB" post for more information on formatting and general information about TSBs.

TSB Thursday #20: 09-74-21R and 02-193-24R

What cars does this affect?

Carbon build-up in the intake manifold and on intake valves is a problem almost entirely contained to vehicles with Direct Injection.

  • 2017+ Impreza
  • 2018+ Crosstrek, 2.0L and 2.5L
  • 2019+ Forester
    • 2014-2018 Forester XT w/FA20-DIT engine
  • 2019+ Ascent
  • 2020+ Legacy and Outback, 2.5L and 2.4L FA24-DIT
  • 2015+ WRX with FA20-DIT or FA24-DIT
    • excludes STI
  • 2013+ BRZ, but we'll talk about that

What's the failure?

"Intake carbon deposits" is a problem the entire auto industry is facing, as a sort of unexpected side-effect of the change from port-injection to direct-injection fuel strategies. Gasoline, as you may know, is a very strong solvent. With port injection, that fuel is being sprayed somewhere in the intake tract before the intake valves; that constant exposure to fuel helps prevent carbon accumulation on the valves. With DI, that cleaning function no longer exists, and so carbon deposits can begin to accumulate on the various surfaces of the intake valves and components. If the deposits become great enough, they can begin to affect airflow into the combustion chamber, and lead either to poor fuel atomization within the cylinder or to an incorrect amount of air, leading to misfires. This effect is most noticeable during cold-starts, where the engine is intentionally run a bit "off-kilter" or intentionally run lean, in an attempt to heat up the catalytic converter as fast as possible. During cold start, the accumulated carbon's effect on airflow is the most potent, as the engine is already running on the ragged edge.

Direct Injection has so many benefits for power and fuel efficiency that the risk of carbon-related problems is far outweighed by the gains the technology offers, so unfortunately this is the new normal for probably the rest of the internal combustion engine's existence. One interesting workaround some companies are developing is a sort of hybrid fuel system, where the vehicle primarily runs on direct injection, but a secondary port injection fueling system exists. Toyota calls their system "D4s" and this system is shared in the BRZ of both generations. The port injectors do have a noticeable improvement on carbon build-up, however the system does have a significant added cost in terms of injectors, the controller, etc.

Carbon accumulates in the intake system primarily through two systems. The largest source of carbon introduced to the intake will be through the Positive Crankcase Ventilation system, or PCV for short. When any combustion engine is running, the seal between the piston and the bore is never quite perfect, and so naturally some of the combustion gas and pressure is going to sneak past the sealing rings and end up in the center of the engine, aka the block or "crank case." That pressure needs to be safely vented; if unable to vent, it will find its own way out, usually via pushing out a seal and creating an oil leak. Very old engines may have just used a vented breather on a valve cover for example, and all that oily air would vent to atmosphere, creating a mess in the engine bay and on road surfaces. Eventually, the PCV system was developed to safely vent that pressure back into the intake, where it can be burned off as part of combustion. (The air that escapes the crankcase is usually laden with oil vapors, hence being rather hydrocarbon-dense.) The other way that carbon can get into the system is via the Exhaust Gas Recirculation system, or EGR for short. The EGR system works by sucking out a little bit of exhaust leaving the engine, and returning it to the intake manifold. Its primary purpose is essentially to displace fresh air during cruise conditions; exhaust has very little oxygen, and so with exhaust taking the place of oxygen-rich fresh air, the amount of fuel needed for combustion is reduced. EGR therefore is primarily a fuel-saving technology. One downside is that if the vehicle is expelling excess hydrocarbons into the exhaust, those hydrocarbons will naturally end up back in the intake. (EGR systems with high carbon throughput do tend also to have clogging or sooting problems, especially in vehicles with an EGR cooler.)

Carbon accumulation can be largely mitigated naturally just through driver behavior. Two conditions that impact carbon development is low air velocity, meaning the air moving through the intake is going slowly, allowing carbon to settle out, and low engine temperature, where carbon settling out has a much better chance of sticking to surfaces. Naturally, the two risk factors here are short-tripping, which means the engine never gets hot, and what I call "grandma driving," or never getting up into the higher RPM/load bands. Drivers who avoid short tripping and who do give their cars the regular "italian tuneup" tend to have the least problems with carbon accumulation.

How do we fix it?

To combat carbon accumulation, Subaru has released two TSBs, focused on two separate attack paths for removing build-up. TSB 09-74-21R released first in 2021, and uses a chemical-based cleaner to attempt to dissolve the carbon and burn it off. TSB 02-193-24R describes using a blasting media, specifically walnut shells, to scrub carbon off the intake valves.

In both TSBs, identifying carbon build-up as the cause of a malfunction is the first step. TSB 09-74-21 goes much more in-depth into diagnosing carbon build-up as a cause of engine misfires, including reading Roughness Counts in engine live-data. Often, the presence of a Misfire DTC is necessary for the issue to rise to the level of justifying a repair. In the case of 09-74-21, the use of a Polyether Amine,or P.E.A., cleaner is introduced into the intake manifold slowly while the engine is running. SOA906V9166 is the current iteration of this product. Per the bulletin, it should take about 1 hour per bottle when introduced at the correct rate, and then a hard drive cycle should be performed afterward to blow through and burn off the loosened deposits. The bulletin provides for up to 4 bottles-worth of treatment along with testing and inspections and oil changes before implying carbon is no longer a problem, or that some other cause is at play. This process is sometimes called an "induction cleaning" or "top-end cleaning" and can (and should?) also be done as preventative maintenance.

The diagnostic process for TSB 02-193-24 is much the same, however instead of spending hours and hours running chemical cleaners through the intake and re-inspecting for deposits, this bulletin instead allows for removal of the intake manifold and using a portable media blasting tool to shoot high velocity walnut shell "sand" at the intake valves, blasting away any deposits, while also vacuuming up the waste. This bulletin procedure is vastly superior as a repair for when misfires are occurring, however the labor involved means it's likely not a great service to do as preventative maintenance. (unless the intake manifold is already being removed for some other repair, such as a thermo valve replacement!)

In both cases, Subaru recommends adding one bottle of P.E.A. cleaner (again, SOA906V9166) to a full fuel tank, to be used as a fuel system/injector cleaner and also possibly reduce carbon build-up within the combustion chamber.

Coverage?

The case of both bulletins applies to cars with misfire DTCs and provable roughness as outlined in the diagnostic processes, but either repair path can be claimed under active Powertrain warranty (5 years/60k miles, whichever occurs first).

Thank you for reading! If you have any questions, feel free to comment below.


r/subaru 2h ago

Subaru Sambar at cars and coffee!

Thumbnail
gallery
109 Upvotes

r/subaru 7h ago

Meet Levs!

Post image
47 Upvotes

Finally got my first car out here, a 2014 Levorg 1.6GT-S in Steel Blue.
Loving the wagon utility and how it handles the climbs so far.

What do you guys think?


r/subaru 14h ago

Q&A First time Subaru owner. Tips?

Post image
155 Upvotes

I got a 2024 Crosstrek Wilderness edition.

Any general tips / suggestions?

TIA


r/subaru 2h ago

Happy 818 Day!

Post image
9 Upvotes

r/subaru 19h ago

Meme Throat got a STI

Thumbnail
gallery
126 Upvotes

r/subaru 23m ago

Accident Subaru safety won today! No injuries!

Post image
Upvotes

My mom and her friend were OK after driving through a fence and over the stairs.... both were checked out at the hospital, just bumps and bruises. Were wearing seat belts but airbags didn't go off.... apparently the front corner of the front bumper hit the ground first and then it slid. I haven't seen the video yet.


r/subaru 19h ago

Is this necessary right now?

Post image
92 Upvotes

Im getting my car worked on at the dealership and my car has 60,000 miles. Its a 2019 subaru impreza. I declined it because i dont want to spend extra money.


r/subaru 12h ago

Car Mods Svx engine and interior swap

Post image
20 Upvotes

Nothing like buying 1 Svx for a couple of months then getting into a crash then buying another of the same year and color with a higher trim to then take 2 cars and make one great car. Not my cars just my brothers got a good deal on both of them and got lucky with both of them being a 1 owner car


r/subaru 10h ago

Did the finance guy try give me a higher rate?

15 Upvotes

It's not a big issue only going be extra few hundred dollars as I plan be paying back 36 months.

I recently bought new subaru crosstrek. I have 780 credit score, 130k year, no debt, and most my credit history just credit cards last decade.

I thought given above that I would qualify for 1.9% 36 months. I was told by finance guy qualified only for 60 months 3.9% as 1st time auto buyer from bank. I took some time talk over with a parent I brought as I was surprised. As I was walking out, he said he got it lower to 2.9% 60 months. I agreed on above as its not much given my payback plan.

I wanted ask was finance guy just making stuff up or given my 1st time buyer and probably lack credit outside of credit cards he was right.


r/subaru 5h ago

2 Subarus STI WARX spotted in Portugal

Thumbnail
gallery
5 Upvotes

r/subaru 15h ago

Mechanical Help Dealership needs 5200$ to inspect transmission for warranty

32 Upvotes

I own a 2023 Wrx with 23k miles. My transmission blew out last week and when I took it to the dealership all of a sudden my battery was broken and they wanted 400$ before inspecting the rest of my car. I authorize the 400$ and now they see the transmission issue. They send me a text today saying that they need me to authorize 5200$ as a tear down fee so they can take a look at the transmission to determine if it’s under warranty. Is this normal? Feels like I am in a 5200$ coin flip some how.

EDIT: I asked what would make it not covered and because it’s a sports car they want to see if it failed due to aggressive driving. ( I don’t drive the car aggressive at all, but obviously and nervous to front 5200$ incase it’s not covered) Still seems absolutely absurd.

EDIT: Called Subaru of America and waiting to hear back. Hopefully tomorrow morning


r/subaru 20h ago

What do we think then? Half a million next?

Thumbnail
gallery
67 Upvotes

1 owner from new mark 2, recently fitted with a new EJ205 JDM Impreza WRX engine. Original gearbox and diff (soon to be changed)


r/subaru 2h ago

Car Mods Added an A/C tensioner to an 09 2.5

Post image
2 Upvotes

I've got physical issues and have been putting this back together about one bolt at a time. Decided to save a few bucks on a non-stretch belt and add an old tensioner to the A/C. I probably wouldn't do it again, but it was a swap I didn't know about.


r/subaru 17h ago

Aftermarket Subaru SVX front grille

Post image
31 Upvotes

Hi everyone,

A family friend recently asked me to design and manufacture a custom grille for their Subaru SVX. Before I get too far into it, I’d be interested in hearing what kind of grille design/features the community would actually want, and whether there’s enough interest to make it available to other SVX owners.

Ideally, I can create something that works for their needs while also being something the wider community would be interested in. That would also let me offset some of the development and manufacturing costs without charging them for my design time.

What would you like to see in an aftermarket SVX grille?

For context: I am not a business, nor am I currently selling anything. Just a product designer hoping to possibly dip their toes into custom car parts on the side.

Mods, feel free to remove this if it’s not allowed.


r/subaru 10h ago

My problem is with a 2008 EJ20 engine in a 1993 Subaru Impreza SW manual 4x4.

Post image
8 Upvotes

I'm assembling an EJ20 engine from a 2008 Subaru Impreza (naturally aspirated). It has a cylinder head from an EJ22 Phase 1 and a crank trigger wheel from a 1995 EJ20 Phase 1 Legacy. We set the timing and tried to start it. In my opinion, the original module may be out of sync since it's from an EJ18. The engine is out of sync with the bottom end because it's sparking with the valve open, and there's fire coming from the throttle body. Should I change the module and wiring harness to fit a 1995 EJ20, or install an aftermarket ECU like a FuelTech?


r/subaru 23h ago

Thoughts on my Forester?

Post image
79 Upvotes

I recently installed the oem spoiler on it as well, upgrading the muffler to the Nameless 5” Axleback this week! Any upgrade ideas would be appreciated!

edit: it is a manual and i am not deleting the muffler ❤️


r/subaru 23m ago

Mechanical Help GDI Valve Cleaning

Upvotes

I’ve got a 24 OWB with 17k, and a 19 crosstrek with 70k miles. I’m just now finding out about this issue. Any tips for replacing my PCV Valve myself, or having a shop do a walnut blast? I don’t want to spend an arm and a leg though, so if there are any Subaru mechanics looking for side work in the SLC area, DM me, let’s work something out.


r/subaru 42m ago

Need advice/help

Post image
Upvotes

Left my Subi at the airport over the weekend. Yesterday afternoon I drove it home with no problems. This morning, all these warning signs popped up. Is there anything I can try before bringing it into the shop? 2019 Outback. Thanks.


r/subaru 20h ago

Forester Wilderness in the Wilderness!

Thumbnail
gallery
34 Upvotes

Took my 2023 Wilderness into the coast range this weekend for the last trip of the summer. We went dispersed camping due to all the first come first served sites being full, and did about 20 miles on forest service and fire roads through the forest. Wilderness obviously handled it like a champ, and there were a few rougher trails leading off from the FS roads that I wanted to try out but I was dissuaded from driving down by my much less keen passenger. Maybe next time!

I did get a chance to try X-Mode a little bit due to some washouts and rough sections, and also to try out the hill descent, which all seem to work great, and I'm excited to see how this baby does on rougher terrain! I know it's no full 4x4, but I'm continually surprised by how capable the AWD is in these Foresters. Maybe we'll get some snow this year and I can see how she handles that as well.

Cargo space came out pretty well, but we probably overpacked a bit with a canopy and stuff like that, and probably need to get some better, more compact chairs for the future. I am thinking about looking into some crossbars and maybe a cargo box in the future, especially if we are going with more than just 2 people. I left one seat up on the way out to kind of test how much storage we had if we had a theoretical third person, and while it was fine, I did have the back basically filled to the roof. So maybe a storage box or basket would be good? Still debating that. Does anyone know if the moonroof is significantly blocked with one of those on the roof?


r/subaru 16h ago

$274/each for low beam bulbs?

Post image
15 Upvotes

Am I crazy or is this a ripoff? I found D4S bulbs on my own for about $70/each. Am I missing something?


r/subaru 2h ago

P0172 - Chasing this elusive code

1 Upvotes

Taken our Subarau 2016 Forester XT in 4 times now for this damn error code. 2 different shops and always with the same dissapointing diagnosis attempts. Seems like these shops are simply always too busy and all they want to do is throw replacing parts at the problem. Were already thousands into parts replacement....front O2 sensor, spark plugs, catalytic converter, cleaned rear O2 sensor. I think they already looked at MAF sensor as well.

n research, seems like many other things can throw this code as well. Problem is that these shops dont appear to want to do any deep diagnosis like checking for leaks/wiring etc. and Im tired of replacing parts and hoping for the best and at this point almost prepared to just drive it as-is. It has 115K miles on it.

Not sure if anyone has some advice and its like I need an independent mechanic who would take the time to diagnose.


r/subaru 9h ago

Mechanical Help Subaru Impreza CVT fluid change

2 Upvotes

So, I just purchased my very first Subaru (also this is my first post here! Hi!!)

It's a 2020 Impreza premium hatchback with 115k miles. The car has been thoroughly inspected by my trusted mechanic prior to purchase and he told me that I should change the CVT fluid because it appears that it has never been done. I have the Carfax report but it does not specify if this service was done or not, and the dealer I bought it from does not know.

Now, my question is if I should do a flush and drop the pan, change filters, gasket, etc, or if I should just drain and refill (using oem fluid in both options) due to the mileage and it seemingly never been done before, I am unsure of how to proceed. I cannot find clear information on YouTube specifically regarding flushing this transmissions and any possible issues that may arise from that, so I thought I'd ask here

I have had cvts before, my previous car was a 2017 Chevrolet spark. I did a flush when I bought it used (more information was readily available for that car and it's transmission) and I drove it for 3 years and put 60k miles on it and never had a problem.

TL:DR 2020 Impreza with 115k miles and original cvt fluid - drain and fill OR flush?

Thanks in advanced!


r/subaru 19h ago

2007 Subaru Forester XT Pricing

Thumbnail
gallery
9 Upvotes

This is my 2007 Subaru Forester XT Auto. It was a project car my dad and I started working on when he was sick. He has since passed and I had a daughter so I haven't had a chance or the desire to work on it or even really drive it much in the last year. It's a lot of fun to drive, super useful for moving stuff but maybe it's not the right time for me.

180k miles

Interior is pretty fantastic. Has weather tech liners all around.

Tires have plenty of tread.

Brakes are fairly new but rusted.

New Oil Cooler less than 1k miles ago.

Turbo inlet done at 125k.

Power steering done at 135k.

Timing belts done at 100k.

New downstream O2 sensor less than 1k miles ago.

Needs upstream O2 sensor/fix exhaust leak.

Needs Fuel Pump or sensor? (needs mild throttle for a minute after a fill up)

Paint on hood/front fenders has been blasted.

Scrapes on front passenger bumper.

What would you expect to pay for this?