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

Donations

If you find this information helpful please consider a donation. These articles, questions and comments are very time consuming so even a small donation gives me motivation to keep educating automotive owners. Donations will allow us to continue open questioning/comments, automotive education and repair tutorials in the future as the business grows. All proceeds go to the expansion and maintenance mdhmotors.com. Thank You



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.

693 Comments

  • Husam says:

    How much do you charge for this job? Including parts and labor.

  • Martin, I’ve got a 2009 Outback 3.0R with 120,k. mi. I’m trying to sort out whether to bend over for the dealer, or have my regular mechanic tackle this. The problem is common to many models. The Generic (and model specific?) error is P0741, which the dealer termed failure of the “2 speed torque converter signal unit and wiring harness.” They want $650 (+/-) for parts and a repair that takes 2 hrs. Parts aren’t stocked at Auto Zone and their readers couldn’t lift the codes. Thought I would take a look at the actual parts when they arrive at the dealer but reserve the right to make a decision whether to buy from them or trust Amazon/EBay. (Eventually, I’ll need their expertise, or someone as friendly as you, and it’s a long way from here to Portland!)

  • George V. says:

    I am looking at a 2018 Subaru Forester with a manual transmission and want to tow it 4 wheels down behind my RV. With the transmission in neutral will I damage the drive train by doing this?

    • Martin Hand Martin Hand says:

      I think it will be okay but I’m not for sure I would ask a tow company or RV shop where they sell the tow bar, they probably have more expeierence with these type of situations.

  • […] w/~120k miles. Binding occurs at low speed when turning. That's about as much as I know. This page has some useful diagnostic info on the more common Subaru AWD problems '07 Eclipse […]

  • Jacob Harding says:

    Hello,
    I have a 2001 Forester L model, Automatic transmission.
    I just finished replacing my bad motor with a lower mileage with fresh head gaskets. I dont believe this has anything to do with the issue I am about to describe but thought I would mention it just in case.
    Here is my issue-Since replacing the motor I noticed a grinding/rubbing noise which is consistent with the rotation of the front axles/wheels when driving. My first thought was possibly a stuck caliper or a warped rotor which I have ruled out. So, I wanted to get a better view of the underside while car was in gear and running so I put all four wheels off the ground and stared it up and put it in drive. So far, so good.
    Now it starts to get weird….
    When I applied throttle I got an awful shudder from the rear. Like the whole rear axle shudders violently under tourqe as soon as throttle is applied. My first suspicion is possible the driveshaft support bearing or possibly worn rear suspension parts causing shutter and shake when tourque is applied. Makes sense, because when the tires are on the ground I would not notice it since these parts have the forces of gravity under the cars weight and momentum to hold them still instead of just free hanging in the air when on jack stands.
    Ok… so now it gets even weirder…..
    I decided not to worry about the rear end noise for now and just go back to diagnosing my front end noise so I decided to put in the FWD fuse to only allow the front wheels to turn while I crawled up under the front end to search for the location of the noise (dangerous,I know, but I am fully aware of the risk I am taking). So, I installed the FWD fuse started the car up and saw that the FWD light was illuminated on the dash. I put the car in drive and stepped out only to find the rear wheel were still SPINNING! I rechecked that the fuse was fully inserted and the indicator light was still on and they were. The rear wheel were spinning slower than before but they would still increase in speed with throttle. One difference though is I can stop them by hand so they are getting very little power. Is this normal?
    Do not worry about trying to answer my front end noise question as I think I will get to the bottom of that (unless it is coming internally from the transmission-but let’s hope not!).
    I would really appreciate your wisdom and input on what may be causing the rear end shutter and if that’s normal or not. Also would like your input on the issue of rear wheels not fully disengaging when FWD fuse is installed.
    I have searched the internet and this site seems to have provided the most relevant information both in your article and your responses to commenters.
    I know it has been a year since the last comment but I hope you will still see my comment.
    Thank-you kindly.

  • […] Subaru All Wheel Drive System Failures & Repair | MDH MOTORS Subaru All Wheel Drive System Failures & Repair. … I am looking at a 2002 Subaru outback sport. its in really nice shape and … Subaru Forester Wind Noise Problem … […]

  • Marshal says:

    I have a 2004 forester that i am converting over for off road use only. I went for test drive today and found out that i have no 8power to the back wheels. I’m going to remove transfer case and check it out. My question is were is the best place to get the parts i will need. Do you have any recommendations. Thank you for your time .

    • Martin Hand Martin Hand says:

      For both AT and MT transmission I buy parts new from Subaru dealer or get good used parts when available. There are a few transmission supply companies that sell used parts here in Portland or buy good used transmission. You can get low mileage AT units from Japan usually only have 40-50K on them, never purchased a used MT transmission though we always just repair those one.

  • Michael Mann says:

    Hi I have a 2005 Subaru Forester just out of the blue drive started slipping. But first second and third do not. Could you please possibly tell me I’m looking at as the problem?

    • Martin Hand Martin Hand says:

      Subaru AT transmissions usually hold up well and have minimal problems. Start by checking tranmission codes and remove the pan and filter to inspect for metal shavings or friction material.

  • Lucas says:

    My wrx sounds like a “baseball card in a bike tire,” it still drives and we’ve been told this is the transfer case issue. They’re quoting a massive price, of course, but I was wondering if you think this is true? Thank you!

    • Martin Hand Martin Hand says:

      I’m assuming it’s a 5spd or 6spd MT transmission? The center differential could have came apart. It will usually pop out the snap ring and that could be rubbing on the transfer case gears. Not uncommon for transfer case failure, especially on the turbo models.

  • Jonathan Salinas says:

    Hi everyone!
    Ok!… so, I need help with this.

    THE CAR: 1996 Subaru Legacy Outback 2.5L DOHC AT AWD NON TURBO

    THE SYMPTOMS: the engine stall out, usually in the middle of a closed turn or when brake to come to a red light (lower RPM), and the AT OIL TEMP & CHECK ENGINE light will flash 16 times. Starts right up and runs perfectly fine afterwards.
    I put the fuse to activate FWD and no change, the engine stall and stop without any difference.

    MY DIAGNOSIS: I read transmission codes using the “secret handshake” method with black B82 conector under the dash, ground out pin#5
    1) Warm up the engine
    2) Turn the ignition switch OFF
    3) Turn the ignition switch ON
    4) Start the engine
    5) Drive the vehicle at speeds greater than 12 MPH
    6) Stop the vehicle
    7) Depress the brake pedal and move the gear selector to “1”
    8 Turn the ignition switch to OFF
    9) Turn the ignition switch to ON
    10) Move the gear selector to “2”
    11) Move the gear selector to “1”
    12) Move the gear selector to “2”
    13) Move the gear selector to “3”
    14) Move the gear selector to “D”

    THE CODES:

    22 Pressure sensor. Short or disconnection in input circuit
    23 Engine speed signal. No signal input above 10km/h
    33 Vehicle speed sensor 2. No signal input to speed Sensor 2 above 20km/h

    MY QUESTIONS:
    Where is the location of these sensors?
    How check the fails in this sensors?
    failure may continue even replacing these sensors according to your experience?

    I read a lot in other forums about “torque bind” problem or “Duty-C” problem, etc… the same symptoms, different solutions. The most common repair is take apart the tail of the transmission and replace a solenoid in this area, also check some damage in the transfer clutch.

    Ok!… so, any ideas?
    Best regards and thanks

    • Martin Hand Martin Hand says:

      I would start by clesaning the throttle body and pcv valve. Then clean the idle air control motor or just replace it, that is probably why the engine is stalling. Clear the codes and drive it to see what comes back they could be false codes.

  • 1 13 14 15

Leave a Reply

Your email address will not be published. Required fields are marked *