The infamous Subaru Front Wheel Drive Fuse, does your Subaru have one? The older Legacy models (maybe 1991 – 1998) have it located under the hood, passenger rear by the firewall. You will see the fuse holder by it self labeled FWD on the lid. I have also seen them in later Outback’s (2000 and newer) in the fuse box under the hood, it’s an empty fuse slot but you will see the diagram on the fuse box showing you which one.
I have had a lot of customers ask me about the FWD fuse for Subaru’s with an automatic transmission. For those who are not aware of this fuse I will explain. There is a fuse holder under the hood that when installed the vehicle will be in front wheel drive mode only. Now, I have been told over the years by different technicians and customers that by installing the FWD fuse and putting the Subaru into front wheel drive mode you can save on gas and get better acceleration (if the traction is good). Others have told me that this is for towing or special service only and not to do this because you can damage the transmission. The prolonged use in front wheel drive mode can cause lubrication problems and what not.
First off I don’t believe there is lubrication problems from driving it in front wheel drive mode. There is always fluid pressure at the solenoid. It’s a duty cycle solenoid meaning it’s pulse width modulated. The computer controls it by on and off pulses in microseconds. When the FWD fuse is in place the solenoid is off and the fluid pressure is by-passed which means the clutch is released. When in AWD mode the clutch is only released when the computer detects a difference in front to rear wheel speed (tight turns). Have you ever tried to drive a 4WD in a tight turn on pavement, if so then you’ll know why this is necessary for an all wheel drive vehicle? Knowing this and working on these units it just don’t make sense why it would hurt the transmission. If it we’re bad to run the vehicle this way then it would not be so easy to get to, right?
I would like to hear some of your responses. Does anyone have a different opinion on the subject? Even if you agree and just have some insight from experience I would love to hear from you. I will be doing more research, read what the factory service manual has to say about it and revise the post. Until then, thank you for reading. Pictures will come soon.
Here is a response I received by a claimed journeyman transmission rebuilder:
If the fuse is left in for long duration of time, The AWD duty solenoid is not powered up & is not allowing hydraulic pressure of the ATF to the viscous clutch drum which risk’s non lubrication & premature wear to the clutches.
After that statement I started thinking and decided I will be doing more extensive research on this subject, this post will be revised, as for now I stand behind my belief that it will not damage the transmission, thank you for reading.