How to remove or add the fuse to make all wheel into 2wdr.

[Petersubaru]

I can't seem to find the info when useing the search...I would like to know how to turn off the all wheel drive ...I had read here a long time ago that it involves the placement or removal of a fuse somewhere under the hood

[Manarius]

I can't seem to find the info when useing the search...I would like to know how to turn off the all wheel drive ...I had read here a long time ago that it involves the placement or removal of a fuse somewhere under the hood

What kind of car do you have? The fuse on the 89-94 Legacies is located on the passenger side strut tower and is labelled FWD.

 

Note: This few only appears on Auto cars. Also, this fuse should only be used for diagnostic purposes as stated in the owner's manual.

[Petersubaru]

I have a 2001 Outback... some time ago I was told by the subi dealer here in my town, that they inform all new drivers about this option???..as a way to pick up a few mpg...no mention was ever made if this applied to automatics only...eventually, I will go in and ask them about this...any further info from you would be appreciated...

What kind of car do you have? The fuse on the 89-94 Legacies is located on the passenger side strut tower and is labelled FWD.

 

Note: This few only appears on Auto cars. Also, this fuse should only be used for diagnostic purposes as stated in the owner's manual.

[Manarius]

I have a 2001 Outback... some time ago I was told by the subi dealer here in my town, that they inform all new drivers about this option???..as a way to pick up a few mpg...no mention was ever made if this applied to automatics only...eventually, I will go in and ask them about this...any further info from you would be appreciated...

FWD fuse does not increase MPG - if anything it can lead to an earlier demise of your automatic transmission. There is no benefit to using the fuse unless you have issues with your car.

 

And yes, this fuse only appears on AUTOMATIC cars only. I'm not sure if it appears on the later cars, but I'm sure that it would be in the owner's manual and it would be labelled as FWD if it existed. So, take a look under your hood and see if you can find it.

[Virrdog]

You already have a spinning driveshaft and rear differential and 2 extra half-shafts. Not transmitting power to them means they are being dragged around. Its more effiecient to just send the power equally to all of the tires since the hardware is in place.

[firstwagon]

I found no difference in mileage when I ran my Legacy in 2wd for a week but am still curious as to why.

 

Look how many manufactors set up their all wheel drive systems to run in front wheel drive until wheel slip is detected (.e. Honda). They claim this is to help fuel mileage. If it made no difference then why not just run it in 50/50 all the time?

 

My Grand Cherokee gets significantly better mileage in 2wd then full time 4wd. However since it has fixed hubs, all the parts are spining all the time there too.

 

Just wondering.... :confused: :confused:

[destey]

I found no difference in mileage when I ran my Legacy in 2wd for a week but am still curious as to why.

 

I'm no expert, but doesn't the ECU pulse the duty C solenoid when it detects wheel slippage? So, am I right in saying the rear wheels are the things turning the rear driveshafts until the solenoid locks up (for that brief instant).

[firstwagon]

I'm no expert, but doesn't the ECU pulse the duty C solenoid when it detects wheel slippage? So, am I right in saying the rear wheels are the things turning the rear driveshafts until the solenoid locks up (for that brief instant).

 

As I understand it, Legacys with automatics run 50/50 in the lower gears and switch to 90/10 in 4th. Manual trans cars run in 50/50 all then time.

[johnceggleston]

i have read wherer later cars, after 97 at least, they moved the fuse in to the fuse box on the left side under the hood. (it may have been 99.)

 

but but all said above is true, no mpg gain, not recommended for long term use.

[BruceyWV]

The Fuse is located in the fuse box in the engine compartment, near the washer reservoir.

[Manarius]

I found no difference in mileage when I ran my Legacy in 2wd for a week but am still curious as to why.

 

Look how many manufactors set up their all wheel drive systems to run in front wheel drive until wheel slip is detected (.e. Honda). They claim this is to help fuel mileage. If it made no difference then why not just run it in 50/50 all the time?

 

My Grand Cherokee gets significantly better mileage in 2wd then full time 4wd. However since it has fixed hubs, all the parts are spining all the time there too.

 

Just wondering.... :confused: :confused:

Jeep's system uses a standard transfer case not a MPT Clutch (like the AWD systems do). So, not engaging that transfer case makes for significant mpg increase versus engaging it.

[porcupine73]

'96 legacy, fuse holder is on firewall near the RH strut tower. '00OBW, FWD fuse in that fuse box near the battery.

 

As far as I understand, the duty c's duty cycle is used to control pressure applied to the clutch pack. 0% duty cycle (off) = full pressure and basically a locked center. 100% duty cycle (on) (i.e. FWD fuse in) = no pressure, thus basically FWD. Normally the duty cycle is controlled to split the power front/rear.

[firstwagon]

Jeep's system uses a standard transfer case not a MPT Clutch (like the AWD systems do). So, not engaging that transfer case makes for significant mpg increase versus engaging it.

 

In 2wd and 4wd high range, the transfer case is the basically the same. Power just passes through it. The centre diff in the Jeep is what you would compare to clutch system in the Subaru.

 

What I don't understand is why a slipping clutch system would be more efficient then a differential.

[johnceggleston]

In 2wd and 4wd high range, the transfer case is the basically the same. Power just passes through it. The centre diff in the Jeep is what you would compare to clutch system in the Subaru.

 

What I don't understand is why a slipping clutch system would be more efficient then a differential.

the transfer case on typical 4WD vehicles is a direct mechanical gearing. every time the output shaft of the tranny makes a revolution, the driver shaft to the rear wheels and the drive shaft to the front wheels also make a revolution (assuming the transfer case is engaged). engageing the transfer case causes the front drive shaft and wheels to turn the same as the rear. this is much more work.

 

the clutch pack on the subaru a/t is computer controlled. most of the time, most of the tranny output is sent to the front wheels, making it mostly a FWD car (not totally, if you put in the FWD fuse you can fell the difference in how the car steers and drives). when the cpmputer detects the front wheels turning at a faster rate than the rear, it sends more output to the rear wheels making it more like a 4WD, (not totally it still has a differencr in power output between the front and rear).

 

and the joy of the AWD is that it usually adjust so quickly to the situation you don't even have time to think about it. you can also manually send power to the rear by shifting the gear selector to D1 or D2. not recommend when traveling 50 mph.

 

when standard 4WD cars are in 4wd, there is a lot more load on the engine than when they operate in 2WD. therefore the MPG goes down. (not to mention that most 4WD vehicles were truck like for the longest time.)

 

subaru AWD does not affect the MPG. there is not real difference between AWD and when you put in the FWD fuse. besides, the system was not designed to run in FWD only, for the long term.

 

if i had to guess, and this is a guess only, true FWD subarus get better gas mileage than similar AWD subarus. (perhaps minimal.)

 

also, subarus do have a differential for both front and rear wheels, the clutch pack is the power distribution unit on the tranny. it's always there , always turning, unlike the typical tranfer case.

 

i hope this helps.

[Petersubaru]

I am wondering also...my all wheel drive VW van gets better mileage when dis-engaged, so I am assuming the subaru can do the same??? ...time will tell

I found no difference in mileage when I ran my Legacy in 2wd for a week but am still curious as to why.

 

Look how many manufactors set up their all wheel drive systems to run in front wheel drive until wheel slip is detected (.e. Honda). They claim this is to help fuel mileage. If it made no difference then why not just run it in 50/50 all the time?

 

My Grand Cherokee gets significantly better mileage in 2wd then full time 4wd. However since it has fixed hubs, all the parts are spining all the time there too.

 

Just wondering.... :confused: :confused:

[BIGBLUE1212]

ive heard mixed stories.....i have a 97 GT and the fwd fuse is on the passengers side at the top of the shock tower....is the all wheel drive engaged when the fuse is in or out?

[porcupine73]

is the all wheel drive engaged when the fuse is in or out?

When the fuse is in, it's FWD b/c the duty c is energized constantly.

[Virrdog]

if i had to guess, and this is a guess only, true FWD subarus get better gas mileage than similar AWD subarus. (perhaps minimal.)

Very true. Less overall weight first of all, and less spinny stuff that robs horsepower along with less friction.

[rweddy]

Look how many manufactors set up their all wheel drive systems to run in front wheel drive until wheel slip is detected (.e. Honda). They claim this is to help fuel mileage. If it made no difference then why not just run it in 50/50 all the time?

 

And this is why Honda,Volvo, Ford, etc systems are inferior to Subaru. These vehicles have to slip to active their awd systems. So you go around an icy corner, the front starts slipping you slide then the AWD kicks in causing you to over correct and you end up in a ditch or worse.

 

Audi and Subaru full time AWD system is much better then those, the manual 50/50 being the best.

[bowjam]

The Fuse is located in the fuse box in the engine compartment, near the washer reservoir.

 

My 99 Impreza w/AT has the FWD in the fuze box under the hood, but there is no fuze in that spot. Do you add a fuze to put it in FWD or take it out.

What amp size fuze ?

[Manarius]

When the fuse is in, it's FWD b/c the duty c is energized constantly.

^^^^^^^^^^^^

 

15 or 20 Amp I think. Owner's manual has the correct spec.

[nipper]

OK when the fuse is in you are telling the TCU to hold the Duty C open. This leads to a burned out solenoid followed by a 1000.00 repair.

 

So any increase in mpg is lost by that repair bill.

 

You can not compare what VW does or Mercedes or honda with Subaru, They all use differnt systems.

 

i find these posts tiring, do a search its been covered many many many many many times.

 

nipper

[johnceggleston]

OK when the fuse is in you are telling the TCU to hold the Duty C open. This leads to a burned out solenoid followed by a 1000.00 repair.

 

So any increase in mpg is lost by that repair bill.

 

You can not compare what VW does or Mercedes or honda with Subaru, They all use differnt systems.

 

i find these posts tiring, do a search its been covered many many many many many times.

 

nipper

 

FYI

i priced the 'duty c' valve assembly at my local dealer yesterday, $94. and that's just the solenoid, not any clutch parts. then 250$ labor to put it in.

[idosubaru]

i've disabled the AWD and even removed parts of the drivetrain. i've done it due to failing u-joints, rear diffs, or other issues and have driven for extensive periods of time like that, so i've seen what it does and does not do to gas mileage.

 

first of all, disabling AWD does not increase MPG. i've done it on automatics and i've done it on manuals. i've disabled the AWD, i've even removed the driveshaft and rear differential from the vehicle and driven it like that. still no increase in gas mileage even with driveshaft and rear differential removed. like nipper said, why bother or risk component damage and the effort working on or worrying about it for little if any possible gain?

 

now, i've told you the end result on multiple vehicles, both automatic and manuals that i've done this too over the years. i'll let everyone else who's never done it debate if it saves gas or doesn't and all they why's and why not's about it.

 

and like others have said, this gets talked about alot and is easily covered with the search function. what you'll get either by searcing or posting a new thread is lots of oppinions.

[Martinjmpr]

As I understand it the main reason for the fuse is for when you have the undersized spare tire on the car. Putting the car in FWD lessens the likelihood that the slightly different tire size will cause damage to the transaxle/AWD system (which, as we know, is very sensitive to differences in tire circumference.)

 

As for the reason there is no appreciable difference in MPG, I think part of the reason is because the Automatics have a 90/10 split in power. IOW, under normal conditions, your front wheels are getting 90% of the power anyway. It's not until you start to slip that the % changes, up to a maximum of 50/50. So, even under the best of circumstances, you would only have a 10% difference in power used and that is probably consumed by all the spinning metal and extra weight (which is still there whether the rear wheels are under power or not.)

 

Contrast this with the MT models which are 50/50 at all times (which also explains whey the MT models don't get any better MPG than the autos.) Presumably a MT car could benefit more from disabling the RWD, but of course the MT cars don't have the ability to disable the rear drive so it's a moot point.