Subaru All Wheel Drive System Failures & Repair

Subaru AWD systems are pretty well designed and failure is not all that common. When you have a failed or failing system there are some things to look for and this article will explain these symptoms and how to repair them without even replacing or removing the transmission. Here are some thing that we will cover.

  • Subaru AWD system common failures

  • How to Identify a Failing Subaru AWD System

  • How to Repair a Subaru AWD Transfercase

Over the 12 years that I have worked on Subaru’s and Subaru transmission repair there are two main parts that have usually fail when you have a problem with the transfer case viscous coupler. The first one is the AWD duty solenoid for applying and releasing the viscous couple when needed. The system needs to allow slip in the clutch when the front and rear tires are rotating at different speeds. This is usually only on turns. When the duty solenoid fails it usually will turn on the AT Oil Temp lite. To retrieve codes for the TCM on older models without a Subaru scanner is a tricky procedure but not that bad once you know it. If you need help in retrieving the diagnostic trouble codes for the TCM contact me for the procedure.

AWD Solenoid Top AWD Solenoid Bottom

Above are a couple pictures of the AWD duty solenoid. Notice how the solenoid comes with its own miniature valve body assembly. This is replaced with the solenoid as an assembly when purchased from a Subaru Dealer. This is the only way I’m aware of how it comes when purchasing a new one and also if there is an aftermarket solenoid available with or without the valve assembly I still wouldn’t recommend it.

The next failure is the most common and even when I have to just do a solenoid you will usually see this problem anyways. The inside viscous clutch drum gets grooves worn on it where the clutch frictions ride on the grooves from the clutches releasing and applying constantly in both directions. What happens when this occurs is as you take a sharp turn under acceleration the clutches bind in the applied position and cannot release. In return you will get a chatter or vibration while turning and acceleration at the same time. This is usually the most common customer complaint that I will hear of. Now regardless if you have solenoid failure or just a worn drum I still recommend to replace both the solenoid and drum. You will also need to replace the clutch pack. The clutches in the old set are usually not burnt up, but they also get worn in the area where the ride against the drum. In extreme failure the drum may even brake like the one I will show you below.

AWD Drum Broken

Broken Subaru AWD viscous clutch drum.

AWD Drum Notches

Worn Subaru viscous clutch drum. Take note of the worn grooves from the clutches.

Subaru All Wheel Drive Transfer Case Repair

Now as I said earlier when you tear down the transmission to repair this system these parts are better off replaced together. So lets go over the needed parts for the repair.

  • AWD duty solenoid and valve assembly
  • solenoid/valve gaskets (2)
  • AWD viscous clutch drum
  • viscous clutch pack set (frictions with steels)
  • transfer case gasket

Now first things first, gets access to the transmission transfer case. Here are the steps I do it in.

  1. remove exhaust
  2. remove heat shield then driveline
  3. remove crossmember and lower transmission down
  4. drain transmission
  5. remove back half of the transmission with transfer case parts (see gallery below)

Now that you have these parts removed it will be pretty self explanatory on the repair now that you know what to look for. Note that the viscous clutch drum has to be pressed of the shaft even though it looks as if the snap ring just holds it on the splines. look over the picture below to get a better idea of what you will encounter and also take note of the park pawl upon removal and assembly, it will only fit one way but it’s possible to get confused here.

This post was written by: Martin Hand

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Martin Hand

About Martin Hand

ASE Certified L1 Advanced Mastertech. Martin Hand has over 15 years experience in Asian and European Import Auto Repair. Specializing in electrical diagnosis, engine performance, AT/MT transmission repair/rebuild. Martin is also pursuing a degree in Computers Science & Information Systems starting at Portland Community College while he plans to transfer to OIT. Certified in Java application level programming, experienced with other languages such as PHP, Ruby, JavaScript and Swift. Martin has future plans of automotive diagnostic software development.

628 Comments

  • Thadd Burch says:

    Had a question about my 07 Subaru Outback. Put a new/used transmission in and the AWD light flashes with no power to the rear wheels. No engine or transmission codes in it. From what I can find, it seems to be the viscous coupler. Am I correct? Thank you for your time.

    • Martin Hand Martin Hand says:

      That doesn’t mean viscous coupler failure, do you have the old transmission? Make sure they are correct, maybe wrong gear ratio. Check if there is a fwd fuse in the underhood fuse box. No codes but the lite is flashing doesn’t make sense. There should be codes set, what type of scanner are you using?

      • Thadd Burch says:

        I have a Solus Edge. The only code was p0301,which I thought was unrelated to the transmission. There is no fuse. I do have the old one yet, and the new/used transmission is from an 05 Impreza. Where would I look for the ratio? The junk yard told me this would work.

        • Martin Hand Martin Hand says:

          P0301 is cylinder number one misfire, not transmission related. You will have to match the numbers on the case or I would trust the place your buying it from they have databases that store this information and are pretty accurate from my experience.

  • Matt Cummins says:

    I have a Subaru Forester XT Auto (model SH5) year 2009. The car won’t engage gear or drive and I changed ATF but it still won’t engage gear or drive at all. I’ve fault code it P0731 “Incorrect first gear ratio” what does it mean ?

    • Martin Hand Martin Hand says:

      The code is setting because when you put it in first gear it doesn’t move and it is supposed to so that is why it says incorrect gear ratio. There is most likely a mechanical problem with the transmission. Make sure it’s full of fluid first

      • Matt Cummins says:

        It is full of ATF but I haven’t got Subaru select monitor to carry out air bleeding of control valve. Would that be normal for you without having main dealer Subaru Select monitor computer in order to bleed the air out of gearbox ??

  • Scott says:

    I have a 2005 forester and I’m having isssues with auto transmission not shifting when under load like climbing a hill. Car will rev at high rims but will not shift. Have to let off and push pedal real slow, still won’t shift until I’m on a down hill grade. Any ideas ?

    • Martin Hand Martin Hand says:

      Check for codes to start, this doesn’t even mean that it is a transmission related problem. If the engine is not running correctly it could also cause these type of problems just by being under powered

  • Gerry says:

    2 quarts of tranny oil dissapearing over the course of oil change (3-4000 miles). 98 sub outback. 240 thousand miles. Been on a lot of dirt & mountain roads. Tranny still doing great. Any common places to look for damaged lines…or maybe just a leaky tran gasket ?

  • Melissa Buchanan says:

    Could you give me a ballpark estimate of how much it would cost (labor and parts) to do the transfer case repair on a 2003 Subaru Forester? Thanks!

    • Martin Hand Martin Hand says:

      Up to $1000 depending if the drum needs replaced or not. I also have to consider the transmission performance, if the transmission has a lot of miles on it or having other issues then your best option is a complete transmission rebuild or remanufactured transmission.

  • Matt says:

    Hi Martin. I have a 2008 Legacy B4. Last week when putting load on the vehicle there was a clunk or jolt felt from the transmission (almost as if car couldn’t find gear). Having taken to a Subaru specialist they traced the issue to inside the transmission with the #2 Torque Converter Turbine Speed Sensor. I understand this is not a replaceable part (part of valve body?). Upon getting a quote for a replacement/second hand tranny, the issue self-corrected, but only 2 days later, started again in the morning. Not sure why the problem is intermittent or why it remedied itself (after re-assembling sump and wiring) – no fault codes have returned. Is this common / leading to a replacement scenario? Thanks

    • Martin Hand Martin Hand says:

      A lot of the newer Subarus have solenoids and sensors that are part of the valve body. The only option is to replace the valve body assembly in this case. I’m not sure with your vehicle but this is what I have seen from experience.

      • Matt says:

        Thanks. Exactly what I’ve had to do – as you describe. 5eat valve body replacement recommended by two Subaru specialists. Expensive down here in NZ…and surprised no cheaper after-market part available.

  • jr says:

    98 forester auto trans rear u joint at trans came apart busted extension housing
    can I remove extension housing on car

  • Paul Thompson says:

    My all- wheel drive doesnt seem to work at all

  • Robert says:

    Hello i have a 2006 Subaru B9 Tribeca with 133k the car runs just fine but i have all kinds of crazy codes coming up. They are as follows, P0709, P1798, P0771,P0301, and P0700. I know the P0301 is a misfire code for cyc1 but the rest seem to be a transmission code that i just cant figure out? I’m wondering if its just one sensor causing this headache? If you have any advice that would be greatly appreciated! Would if be wise to replace the whole transmission as a complete assembly?

    • Martin Hand Martin Hand says:

      Start by clearing the codes, test drive the vehicle to see what codes return. Most likely multiple codes are setting due to one type of failure. Yes you are correct the cylinder misfire (P0301) is a separate issue though.

  • dave says:

    Hi. My 2002 Outback was hit recently and I thought it to be just a fender bender. Other driver hit my driver side fender near the head light at a good clip. It was a fairly direct hit but I didn’t seem to feel it much.

    Anyways I thought maybe the battery could have got damaged and some fuses near there.

    I drove off and less than a mile on a right turn with acceleration up a bridge ramp my tranny stopped functioning. I didn’t smell anything and calmly let it roll back to flat ground. I got out and there was fluid dripping heavily. There was no leak of any sort at the accident location.

    I found a local shop and they replaced two lines apparently only to find that it still didn’t work. They said I probably burned up the tranny when I lost the fluid.

    My question is whether the abrupt nature in which the tranny ceased to work is a sign that it is burned up?

    Thanks. I don’t want to replace a tranny if it is reparable.

    Best regards, Dave

  • dave says:

    Hi. My 2002 Outback was hit recently and I thought it to be just a fender bender. Other driver hit my driver side fender near the head light at a good clip. It was a fairly direct hit but I didn’t seem to feel it much.

    Anyways I thought maybe the battery could have got damaged and some fuses near there.

    I drove off and less than a mile on a right turn with acceleration up a bridge ramp my tranny stopped functioning. I didn’t smell anything and calmly let it roll back to flat ground. I got out and there was fluid dripping heavily. There was no leak of any sort at the accident location.

    I found a local shop and they replaced two lines apparently only to find that it still didn’t work. They said I probably burned up the tranny when I lost the fluid.

    My question is if whether the abrupt nature in which the tranny ceased to work a sign that it is burned up?

    Thanks. I don’t want to replace a tranny if it is reparable.

  • Shelu Jha says:

    Hi I seem to be having problems with AT for my Subaru Impreza 1.5 4WD but I am just guessing. These days I find she doesn’ t accelarate well enough and at higher speeds (above 50) gives a continuous humming noise. Giving me an impression gear shifting is not good enough. Could you please help me with this.

  • Natalia says:

    Thank you for the great site!
    I would be grateful for your advice – I have 1998 Subary Legacy 4WD auto /turbo / Japanese built (64K). In a morning when car is still cold – I shift the gear to D and car jerks/ makes a little jump. I had a couple incidents when gear was in drive, but car would not move – I shifted gear back and forward and car started to move. It didn’t repeat after I’ve changed transmission fluid.
    One shop told me that I need engine tune up, another guy told me that my transmission should be replaced. Just want to know what you think

    • Martin Hand Martin Hand says:

      That is not good advice. You need to have the problem accurately diagnosed first. Keep driving to see if problem is progressively more consistent or intermittent still. I wouldn’t worry about it for now unless it’s consistent problem.

      • Kate says:

        What causes it to fail? Uneven tire wear?
        At 15,000 miles on our 2015 Subaru Forester, we picked up a big screw in one of our tires in the Home Depot parking lot, and our Subaru service department said we did not need to replace all four tires. Now, 1800 miles later, when getting our oil changed with our local guy, he says the old tires have 9/32 wear and the new one 6/32 wear, which is dangerous and will cause the transmission to fail.
        We will take it back to Subaru next week for them to look at.
        Any thoughts or advice?
        Thank you.

  • philip potts says:

    Hi just bought a 2006 auto legacy from auction only 108000k’s But ,there’s always a but, it has the engine malfunction light and the blinking cruise light on.As well it has the chatting at slow speed turn not noisy but you can feel it I feel this may have been covered but could you supply any tips

    • philip potts says:

      Forgot to say it has a triptonic auto

      • Tucker says:

        The engine/cruise light is probably related to the O2 sensor. Subaru has a recall on it, as it can develop a crack. I bet if you disconnect the battery for 15 seconds, the light will go away because you’ve reset the codes. But because of the crack, it will come back. 02 sensor will probably run you about $150.
        -Tucker, 2005 Outback owner

    • Martin Hand Martin Hand says:

      Check codes to see why CEL on and possibly needs a transfer case repair. Contact us to schedule an appointment okay thanks

  • Michael Levine says:

    Hello from California:
    2006 Outback 2.5XT Limited. 5 speed automatic trans., 135,000 miles, original owner. All service has been done per schedule since car was new. Last week started to notice something I’ve never experienced before with this car. Holding freeway speed (60 – 70 mph) in 5th gear with pedal only or with cruise control and then accelerating with moderate pressure on gas pedal I feel one “buck” or “lurch” (sounds like a “clunk) as the car downshifts. It doesn’t do it all the time. Normally the car will smoothly downshift as power increases. I’ve checked for codes with OBD II scanner …. none, and no other warning lights have come on. Should I be concerned and what should I do?

    Thanks in advance for your help/comment on this.
    Mike

    • Martin Hand Martin Hand says:

      The transmissions will do this sometimes and have nothing wrong. Probably just related to the specific driving conditions. I wouldn’t worry about it unless the problem becomes progressively worse and more consistent.

  • jaeger engberg says:

    i jut put a new transmission in my 2005 subaru sti. when i drive it it has a strong shake unless i let off the gas or push in clutch. if i take my dccd out of auto into the open position the shake is alot less significant.(basically gone) if i move the dccd into lock the shaking happens again. i have put after market cv axles new excedy stage one clutch and act lightened flywheel. any suggestions on where to start feels like diffrent gear ratios almost!
    thanks in advance

    • jaeger engberg says:

      this is the second transmission ive put in with the same problem

    • Martin Hand Martin Hand says:

      Start by checking the obvious: cv axles, driveline carrier and u-joints, rear differential, even tire/wheel size. Try running it in the air to see if there is uneven wheel speed. I don’t ever replace the transmissions and less I have to. Do you have the original transmission? I would repair that one

  • alan liu says:

    Very insightful and helpful site! I recently replaced the solenoid in my 02 forester. It used to bind to the point where the car does not move unless you give some gas. But after replacing the solenoid i can still feel a binding feel when I turn. I’m thinking its the drum and clutch pack set. Would you happen to have the part numbers for the drum and clutch pack set?

    • Martin Hand Martin Hand says:

      I don’t keep part numbers for that type of repair they change between models and years too much. Contact Subaru dealer and pick out what you need from the parts diagram.

  • Nick says:

    Hay, i am having issues with my 2005 Subaru impraza AUTO transmission. the problem starts when i am going at low speed and taking a sharp, left or a right turn. and the whole care shacks, but when i am going strate every thing is fine. i also did a test by putting my subaru in to 2WD and had no issue when i took a sharp turn, every thing went back to normal. but puting 4wd the problem comes back, pleas HELP.

    • Martin Hand Martin Hand says:

      Sounds like the same problem that’s described in this article. Are you near Portland Oregon? I would need you to bring it bye so I can check it out. Check for transmission diagnostic trouble codes.

  • Rick Gargano says:

    I have a 2006 Subaru Forester manual transmission . I was driving it on the freeway and now it will engage in all gear but it won’t go. Can you tell me what this could be?

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